diff --git a/toolchain/base/BUILD b/toolchain/base/BUILD
index 73f63ba15d17..f2cee9e76fd2 100644
--- a/toolchain/base/BUILD
+++ b/toolchain/base/BUILD
@@ -72,7 +72,9 @@ cc_library(
         "@llvm-project//clang:basic",
         "@llvm-project//clang:driver",
         "@llvm-project//clang:frontend",
+        "@llvm-project//llvm:MC",
         "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
     ],
 )
 
diff --git a/toolchain/base/clang_invocation.cpp b/toolchain/base/clang_invocation.cpp
index eefc3ad89d2f..f1a61057381b 100644
--- a/toolchain/base/clang_invocation.cpp
+++ b/toolchain/base/clang_invocation.cpp
@@ -7,14 +7,21 @@
 #include <filesystem>
 #include <string>
 
+#include "clang/Basic/DiagnosticDriver.h"
+#include "clang/Basic/TargetInfo.h"
 #include "clang/Driver/CreateInvocationFromArgs.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/Utils.h"
 #include "common/string_helpers.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/MC/MCSubtargetInfo.h"
+#include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/FormatVariadic.h"
+#include "llvm/TargetParser/SubtargetFeature.h"
+#include "llvm/TargetParser/Triple.h"
 
 namespace Carbon {
 
@@ -50,17 +57,51 @@ auto ClangDriverDiagnosticConsumer::HandleDiagnostic(
   }
 }
 
+// Validates `target_opts` (such as `-march`, `-mcpu`, `-mtune`, and
+// `-target-feature`) and canonicalizes `target_opts.Features` via
+// `clang::TargetInfo::CreateTargetInfo`. Returns `false` if any target option
+// or feature is invalid.
+static auto ValidateTargetOptions(clang::DiagnosticsEngine& driver_diags,
+                                  clang::TargetOptions& target_opts) -> bool {
+  llvm::IntrusiveRefCntPtr<clang::TargetInfo> target_info(
+      clang::TargetInfo::CreateTargetInfo(driver_diags, target_opts));
+
+  // `TargetInfo::CreateTargetInfo` expands Clang-level feature aliases into
+  // `TargetOptions::Features`, but passes unknown `+feature`/`-feature`
+  // entries through to the backend where `MCSubtargetInfo` only prints a raw
+  // stderr warning. Validate that every canonicalized backend feature is
+  // recognized by the target's `MCSubtargetInfo` when the target is registered.
+  std::string target_error;
+  llvm::Triple triple(target_opts.Triple);
+  if (const llvm::Target* target =
+          llvm::TargetRegistry::lookupTarget(triple, target_error)) {
+    std::unique_ptr<llvm::MCSubtargetInfo> subtarget_info(
+        target->createMCSubtargetInfo(triple, /*CPU=*/"", /*Features=*/""));
+    if (subtarget_info) {
+      llvm::ArrayRef<llvm::SubtargetFeatureKV> valid_features =
+          subtarget_info->getAllProcessorFeatures();
+      const auto& features =
+          target_info ? target_opts.Features : target_opts.FeaturesAsWritten;
+      for (llvm::StringRef feature : features) {
+        llvm::StringRef name = llvm::SubtargetFeatures::StripFlag(feature);
+        const auto* it = llvm::lower_bound(valid_features, name);
+        if (it == valid_features.end() || llvm::StringRef(it->key()) != name) {
+          driver_diags.Report(clang::diag::err_drv_unsupported_option_argument)
+              << "-target-feature" << feature;
+        }
+      }
+    }
+  }
+
+  return target_info && !driver_diags.hasErrorOccurred();
+}
+
 auto BuildClangInvocation(Diagnostics::Consumer& consumer,
                           llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
                           const InstallPaths& install_paths,
                           llvm::StringRef target_str,
                           llvm::ArrayRef<llvm::StringRef> extra_args)
     -> std::unique_ptr<clang::CompilerInvocation> {
-  Diagnostics::ErrorTrackingConsumer error_tracker(consumer);
-  Diagnostics::NoLocEmitter emitter(&error_tracker);
-
-  ClangDriverDiagnosticConsumer diagnostics_consumer(&emitter);
-
   llvm::SmallVector<std::string> args;
   args.push_back("--start-no-unused-arguments");
   AppendDefaultClangArgs(install_paths, target_str, args);
@@ -83,6 +124,8 @@ auto BuildClangInvocation(Diagnostics::Consumer& consumer,
 
   // Build a diagnostics engine. Note that we don't have any diagnostic options
   // yet; they're produced by running the driver.
+  Diagnostics::NoLocEmitter emitter(&consumer);
+  ClangDriverDiagnosticConsumer diagnostics_consumer(&emitter);
   clang::DiagnosticOptions driver_diag_opts;
   llvm::IntrusiveRefCntPtr<clang::DiagnosticsEngine> driver_diags(
       clang::CompilerInstance::createDiagnostics(*fs, driver_diag_opts,
@@ -91,23 +134,22 @@ auto BuildClangInvocation(Diagnostics::Consumer& consumer,
 
   // Ask the driver to process the arguments and build a corresponding clang
   // frontend invocation.
-  auto invocation =
+  std::unique_ptr<clang::CompilerInvocation> invocation =
       clang::createInvocation(cstr_args, {.Diags = driver_diags, .VFS = fs});
 
   // If Clang produced an error, throw away its invocation.
-  if (error_tracker.seen_error()) {
+  if (!invocation || driver_diags->hasErrorOccurred() ||
+      !ValidateTargetOptions(*driver_diags, invocation->getTargetOpts())) {
     return nullptr;
   }
 
-  if (invocation) {
-    // Track submodule visibility in the preprocessor and Sema.
-    invocation->getLangOpts().Modules = true;
-    invocation->getLangOpts().ModulesLocalVisibility = true;
+  // Track submodule visibility in the preprocessor and Sema.
+  invocation->getLangOpts().Modules = true;
+  invocation->getLangOpts().ModulesLocalVisibility = true;
 
-    // Do not emit Clang's name and version as the creator of the output file.
-    invocation->getCodeGenOpts().EmitVersionIdentMetadata = false;
-    invocation->getCodeGenOpts().DiscardValueNames = false;
-  }
+  // Do not emit Clang's name and version as the creator of the output file.
+  invocation->getCodeGenOpts().EmitVersionIdentMetadata = false;
+  invocation->getCodeGenOpts().DiscardValueNames = false;
 
   return invocation;
 }
diff --git a/toolchain/base/clang_invocation.h b/toolchain/base/clang_invocation.h
index 258dde9c8f74..903e9a6cf6a5 100644
--- a/toolchain/base/clang_invocation.h
+++ b/toolchain/base/clang_invocation.h
@@ -5,6 +5,7 @@
 #ifndef CARBON_TOOLCHAIN_BASE_CLANG_INVOCATION_H_
 #define CARBON_TOOLCHAIN_BASE_CLANG_INVOCATION_H_
 
+#include <memory>
 #include <string>
 
 #include "clang/Basic/Diagnostic.h"
@@ -37,8 +38,10 @@ class ClangDriverDiagnosticConsumer : public clang::DiagnosticConsumer {
 };
 
 // Builds and returns a clang `CompilerInvocation` to use when building code for
-// interop, from a list of clang driver arguments. Emits diagnostics to
-// `consumer` if the arguments are invalid.
+// interop, from a list of clang driver arguments. Validates the target options
+// and canonicalizes `TargetOptions::Features` via
+// `clang::TargetInfo::CreateTargetInfo`. Emits diagnostics to `consumer` if the
+// arguments or target options are invalid.
 auto BuildClangInvocation(Diagnostics::Consumer& consumer,
                           llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
                           const InstallPaths& install_paths,
diff --git a/toolchain/check/cpp/generate_ast.cpp b/toolchain/check/cpp/generate_ast.cpp
index b84b25d3167b..50d5230cd3af 100644
--- a/toolchain/check/cpp/generate_ast.cpp
+++ b/toolchain/check/cpp/generate_ast.cpp
@@ -14,6 +14,7 @@
 #include "clang/Basic/DiagnosticParse.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/Module.h"
+#include "clang/Basic/TargetOptions.h"
 #include "clang/CodeGen/ModuleBuilder.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/CompilerInvocation.h"
@@ -103,6 +104,7 @@ class ShallowCopyCompilerInvocation : public clang::CompilerInvocation {
     // Make a deep copy of options that we modify.
     FrontendOpts = std::make_shared<clang::FrontendOptions>(*FrontendOpts);
     PPOpts = std::make_shared<clang::PreprocessorOptions>(*PPOpts);
+    TargetOpts = std::make_shared<clang::TargetOptions>(*TargetOpts);
   }
 };
 
diff --git a/toolchain/driver/BUILD b/toolchain/driver/BUILD
index 97559d31ae12..328a17af23d8 100644
--- a/toolchain/driver/BUILD
+++ b/toolchain/driver/BUILD
@@ -26,6 +26,7 @@ cc_library(
         "clang_runtimes.h",
     ],
     deps = [
+        ":codegen_options",
         ":llvm_runner",
         ":runtimes_cache",
         ":tool_runner_base",
@@ -41,6 +42,7 @@ cc_library(
         "//toolchain/base:install_paths",
         "//toolchain/base:kind_switch",
         "//toolchain/base:runtimes_build_info",
+        "//toolchain/diagnostics:emitter",
         "@llvm-project//clang:basic",
         "@llvm-project//clang:clang-driver",
         "@llvm-project//clang:codegen",
@@ -62,6 +64,7 @@ cc_test(
     data = ["//toolchain/install:install_data"],
     deps = [
         ":clang_runner",
+        ":codegen_options",
         ":llvm_runner",
         ":runtimes_cache",
         "//common:all_llvm_targets",
@@ -74,6 +77,7 @@ cc_test(
         "//testing/base:global_exe_path",
         "//testing/base:gtest_main",
         "//toolchain/base:install_paths",
+        "//toolchain/diagnostics:null_diagnostics",
         "@googletest//:gtest",
         "@llvm-project//llvm:Object",
         "@llvm-project//llvm:Support",
@@ -91,6 +95,7 @@ cc_test(
     ],
     deps = [
         ":clang_runner",
+        ":codegen_options",
         ":llvm_runner",
         ":runtimes_cache",
         "//common:all_llvm_targets",
@@ -103,6 +108,7 @@ cc_test(
         "//testing/base:gtest_main",
         "//toolchain/base:install_paths",
         "//toolchain/base:llvm_tools",
+        "//toolchain/diagnostics:null_diagnostics",
         "@bazel_tools//tools/cpp/runfiles",
         "@googletest//:gtest",
         "@llvm-project//llvm:Object",
@@ -203,6 +209,7 @@ cc_library(
         "//toolchain/parse:tree",
         "//toolchain/sem_ir:typed_insts",
         "//toolchain/source:source_buffer",
+        "@llvm-project//clang:basic",
         "@llvm-project//llvm:Core",
         "@llvm-project//llvm:MC",
         "@llvm-project//llvm:Passes",
@@ -485,6 +492,7 @@ cc_test(
         "@googletest//:gtest",
         "@llvm-project//llvm:Object",
         "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
     ],
 )
 
diff --git a/toolchain/driver/build_runtimes_subcommand.cpp b/toolchain/driver/build_runtimes_subcommand.cpp
index a1f133ad4d1e..42668fced6cb 100644
--- a/toolchain/driver/build_runtimes_subcommand.cpp
+++ b/toolchain/driver/build_runtimes_subcommand.cpp
@@ -82,8 +82,9 @@ auto BuildRuntimesSubcommand::RunInternal(DriverEnv& driver_env)
   ClangRunner runner(driver_env.installation, driver_env.fs,
                      driver_env.vlog_stream);
 
-  Runtimes::Cache::Features features = {
-      .target = options_.codegen_options.target.str()};
+  CARBON_ASSIGN_OR_RETURN(Runtimes::Cache::Features features,
+                          runner.ComputeRuntimesFeatures(
+                              options_.codegen_options, *driver_env.consumer));
 
   bool is_cache = options_.directory.empty();
   std::filesystem::path output_path = options_.directory.str();
@@ -102,14 +103,11 @@ auto BuildRuntimesSubcommand::RunInternal(DriverEnv& driver_env)
   }
 
   ClangResourceDirBuilder resource_dir_builder(&runner, driver_env.thread_pool,
-                                               llvm::Triple(features.target),
-                                               &runtimes);
+                                               &runtimes, features);
   ClangArchiveRuntimesBuilder<Runtimes::LibUnwind> lib_unwind_builder(
-      &runner, driver_env.thread_pool, llvm::Triple(features.target),
-      &runtimes);
+      &runner, driver_env.thread_pool, &runtimes, features);
   ClangArchiveRuntimesBuilder<Runtimes::Libcxx> libcxx_builder(
-      &runner, driver_env.thread_pool, llvm::Triple(features.target),
-      &runtimes);
+      &runner, driver_env.thread_pool, &runtimes, features);
   CarbonPreludeBuilder prelude_builder(&driver_env, &runtimes,
                                        &options_.codegen_options);
 
diff --git a/toolchain/driver/carbon_runtimes.cpp b/toolchain/driver/carbon_runtimes.cpp
index f89cd7f36a9f..06fe3702fb17 100644
--- a/toolchain/driver/carbon_runtimes.cpp
+++ b/toolchain/driver/carbon_runtimes.cpp
@@ -102,11 +102,14 @@ auto CarbonPreludeBuilder::Build() && -> ErrorOr<std::filesystem::path> {
             absolute_output_path.parent_path());
         return absolute_output_path.string();
       });
-  CARBON_CHECK(init_result,
-               "Failed to initialize compiler driver for Carbon prelude.");
+  if (!init_result) {
+    return Error("Failed to initialize compiler driver for Carbon prelude.");
+  }
 
   auto compile_result = compile_driver_.Compile(*driver_env_);
-  CARBON_CHECK(compile_result.success, "Failed to compile Carbon prelude.");
+  if (!compile_result.success) {
+    return Error("Failed to compile Carbon prelude.");
+  }
 
   result_ = (*std::move(runtimes_builder_)).Commit();
   return std::move(result_);
diff --git a/toolchain/driver/clang_runner.cpp b/toolchain/driver/clang_runner.cpp
index 03fc5e505970..b3cb155929b2 100644
--- a/toolchain/driver/clang_runner.cpp
+++ b/toolchain/driver/clang_runner.cpp
@@ -8,19 +8,19 @@
 #include <unistd.h>
 
 #include <filesystem>
+#include <iterator>
 #include <memory>
 #include <optional>
 #include <string>
 #include <utility>
 
 #include "clang/Basic/Diagnostic.h"
-#include "clang/Basic/DiagnosticDriver.h"
 #include "clang/Basic/DiagnosticIDs.h"
 #include "clang/Basic/DiagnosticOptions.h"
+#include "clang/Basic/TargetOptions.h"
 #include "clang/CodeGen/ObjectFilePCHContainerWriter.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
-#include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/TextDiagnosticBuffer.h"
 #include "clang/Frontend/TextDiagnosticPrinter.h"
@@ -151,6 +151,31 @@ static auto IsNonLinkCommand(llvm::ArrayRef<llvm::StringRef> args) -> bool {
   });
 }
 
+auto ClangRunner::ComputeRuntimesFeatures(const CodegenOptions& codegen_options,
+                                          Diagnostics::Consumer& consumer)
+    -> ErrorOr<Runtimes::Cache::Features> {
+  llvm::SmallVector<std::string> codegen_clang_args =
+      codegen_options.GetClangArgs();
+  llvm::SmallVector<llvm::StringRef> extra_args(codegen_clang_args.begin(),
+                                                codegen_clang_args.end());
+  std::unique_ptr<clang::CompilerInvocation> invocation = BuildClangInvocation(
+      consumer, fs_, *installation_, codegen_options.target, extra_args);
+  if (!invocation) {
+    return Error(
+        llvm::formatv("Unable to setup target `{0}`", codegen_options.target)
+            .str());
+  }
+  clang::TargetOptions& target_opts = invocation->getTargetOpts();
+  return Runtimes::Cache::Features{
+      .target = codegen_options.target.str(),
+      .cpu = std::move(target_opts.CPU),
+      .tune_cpu = std::move(target_opts.TuneCPU),
+      .target_features = llvm::SmallVector<std::string>(
+          std::make_move_iterator(target_opts.Features.begin()),
+          std::make_move_iterator(target_opts.Features.end())),
+  };
+}
+
 auto ClangRunner::RunWithPrebuiltRuntimes(llvm::ArrayRef<llvm::StringRef> args,
                                           Runtimes& prebuilt_runtimes,
                                           bool enable_leaking)
@@ -179,7 +204,8 @@ auto ClangRunner::RunWithPrebuiltRuntimes(llvm::ArrayRef<llvm::StringRef> args,
 auto ClangRunner::Run(llvm::ArrayRef<llvm::StringRef> args,
                       Runtimes::Cache& runtimes_cache,
                       llvm::ThreadPoolInterface& runtimes_build_thread_pool,
-                      bool enable_leaking) -> ErrorOr<bool> {
+                      bool enable_leaking, Runtimes::Cache::Features features)
+    -> ErrorOr<bool> {
   std::string target = ComputeClangTarget(args);
 
   // Check the args to see if we have a known target-independent command. If so,
@@ -198,7 +224,9 @@ auto ClangRunner::Run(llvm::ArrayRef<llvm::StringRef> args,
                        enable_leaking);
   }
 
-  Runtimes::Cache::Features features = {.target = target};
+  if (features.target.empty()) {
+    features.target = target;
+  }
   CARBON_ASSIGN_OR_RETURN(Runtimes runtimes, runtimes_cache.Lookup(features));
 
   // We need to build the Clang resource directory for these runtimes. This
@@ -206,14 +234,12 @@ auto ClangRunner::Run(llvm::ArrayRef<llvm::StringRef> args,
   // the build. The temporary directory should only be used during the build,
   // not once we are running Clang with the built runtime.
   CARBON_VLOG("Building target resource dir...\n");
-  ClangResourceDirBuilder builder(this, &runtimes_build_thread_pool,
-                                  llvm::Triple(features.target), &runtimes);
+  ClangResourceDirBuilder builder(this, &runtimes_build_thread_pool, &runtimes,
+                                  features);
   ClangArchiveRuntimesBuilder<Runtimes::LibUnwind> lib_unwind_builder(
-      this, &runtimes_build_thread_pool, llvm::Triple(features.target),
-      &runtimes);
+      this, &runtimes_build_thread_pool, &runtimes, features);
   ClangArchiveRuntimesBuilder<Runtimes::Libcxx> libcxx_builder(
-      this, &runtimes_build_thread_pool, llvm::Triple(features.target),
-      &runtimes);
+      this, &runtimes_build_thread_pool, &runtimes, features);
   CARBON_ASSIGN_OR_RETURN(std::filesystem::path resource_dir_path,
                           std::move(builder).Wait());
   CARBON_ASSIGN_OR_RETURN(std::filesystem::path libunwind_path,
diff --git a/toolchain/driver/clang_runner.h b/toolchain/driver/clang_runner.h
index 309c4d2e6307..f66f3d76e4b1 100644
--- a/toolchain/driver/clang_runner.h
+++ b/toolchain/driver/clang_runner.h
@@ -19,6 +19,8 @@
 #include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/TargetParser/Triple.h"
 #include "toolchain/base/install_paths.h"
+#include "toolchain/diagnostics/emitter.h"
+#include "toolchain/driver/codegen_options.h"
 #include "toolchain/driver/runtimes_cache.h"
 #include "toolchain/driver/tool_runner_base.h"
 
@@ -83,7 +85,8 @@ class ClangRunner : ToolRunnerBase {
   auto Run(llvm::ArrayRef<llvm::StringRef> args,
            Runtimes::Cache& runtimes_cache,
            llvm::ThreadPoolInterface& runtimes_build_thread_pool,
-           bool enable_leaking = false) -> ErrorOr<bool>;
+           bool enable_leaking = false, Runtimes::Cache::Features features = {})
+      -> ErrorOr<bool>;
 
   // Run Clang with the provided arguments and prebuilt runtimes.
   //
@@ -104,6 +107,13 @@ class ClangRunner : ToolRunnerBase {
   auto RunWithNoRuntimes(llvm::ArrayRef<llvm::StringRef> args,
                          bool enable_leaking = false) -> ErrorOr<bool>;
 
+  // Computes the canonicalized `Runtimes::Cache::Features` for
+  // `codegen_options`, emitting any diagnostics for invalid target flags to
+  // `consumer`.
+  auto ComputeRuntimesFeatures(const CodegenOptions& codegen_options,
+                               Diagnostics::Consumer& consumer)
+      -> ErrorOr<Runtimes::Cache::Features>;
+
  private:
   friend class ClangRuntimesBuilderBase;
 
diff --git a/toolchain/driver/clang_runner_test.cpp b/toolchain/driver/clang_runner_test.cpp
index 456d0969fdc2..9c47e693b7a9 100644
--- a/toolchain/driver/clang_runner_test.cpp
+++ b/toolchain/driver/clang_runner_test.cpp
@@ -24,13 +24,20 @@
 #include "testing/base/file_helpers.h"
 #include "testing/base/global_exe_path.h"
 #include "toolchain/base/install_paths.h"
+#include "toolchain/diagnostics/null_diagnostics.h"
+#include "toolchain/driver/codegen_options.h"
 #include "toolchain/driver/runtimes_cache.h"
 
 namespace Carbon {
 namespace {
 
+using ::testing::_;
+using ::testing::Contains;
 using ::testing::HasSubstr;
+using ::testing::IsEmpty;
+using Testing::IsError;
 using Testing::IsSuccess;
+using ::testing::Not;
 using ::testing::StrEq;
 
 class ClangRunnerTest : public ::testing::Test {
@@ -278,5 +285,154 @@ _Z4testv:
   EXPECT_THAT(err, StrEq(""));
 }
 
+TEST_F(ClangRunnerTest, ComputeRuntimesFeatures) {
+  ClangRunner runner(&install_paths_, vfs_);
+  auto compute = [&](const CodegenOptions& options) {
+    return runner.ComputeRuntimesFeatures(options, Diagnostics::NullConsumer());
+  };
+
+  // x86_64: default, microarchitecture level, specific CPU, and tune CPU.
+  auto x86_default = compute({.target = "x86_64-unknown-linux-gnu"});
+  ASSERT_THAT(x86_default, IsSuccess(_));
+  EXPECT_THAT(x86_default->cpu, StrEq("x86-64"));
+  EXPECT_THAT(x86_default->tune_cpu, StrEq("generic"));
+
+  auto x86_v3 = compute(
+      {.target = "x86_64-unknown-linux-gnu", .target_cpu = "x86-64-v3"});
+  ASSERT_THAT(x86_v3, IsSuccess(_));
+  EXPECT_THAT(x86_v3->cpu, StrEq("x86-64-v3"));
+  EXPECT_THAT(x86_v3->tune_cpu, IsEmpty());
+  EXPECT_THAT(x86_v3->target_features, Contains("+avx2"));
+  EXPECT_THAT(x86_v3->target_features, Contains("+bmi2"));
+
+  auto x86_v3_tuned = compute({.target = "x86_64-unknown-linux-gnu",
+                               .target_cpu = "x86-64-v3",
+                               .target_cpu_tune = "znver4"});
+  ASSERT_THAT(x86_v3_tuned, IsSuccess(_));
+  EXPECT_THAT(x86_v3_tuned->cpu, StrEq("x86-64-v3"));
+  EXPECT_THAT(x86_v3_tuned->tune_cpu, StrEq("znver4"));
+
+  auto x86_znver4 =
+      compute({.target = "x86_64-unknown-linux-gnu", .target_cpu = "znver4"});
+  ASSERT_THAT(x86_znver4, IsSuccess(_));
+  EXPECT_THAT(x86_znver4->cpu, StrEq("znver4"));
+  EXPECT_THAT(x86_znver4->tune_cpu, IsEmpty());
+  EXPECT_THAT(x86_znver4->target_features, Contains("+avx512f"));
+
+  // AArch64: architecture string (-march), CPU name (-mcpu), and tune (-mtune).
+  auto aarch64_v9 = compute({.target = "aarch64-unknown-linux-gnu",
+                             .target_cpu = "armv9-a",
+                             .target_cpu_tune = "neoverse-v2"});
+  ASSERT_THAT(aarch64_v9, IsSuccess(_));
+  EXPECT_THAT(aarch64_v9->tune_cpu, StrEq("neoverse-v2"));
+  EXPECT_THAT(aarch64_v9->target_features, Contains("+v9a"));
+  EXPECT_THAT(aarch64_v9->target_features, Contains("+sve2"));
+
+  auto aarch64_neoverse = compute(
+      {.target = "aarch64-unknown-linux-gnu", .target_cpu = "neoverse-v2"});
+  ASSERT_THAT(aarch64_neoverse, IsSuccess(_));
+  EXPECT_THAT(aarch64_neoverse->cpu, StrEq("neoverse-v2"));
+  EXPECT_THAT(aarch64_neoverse->tune_cpu, IsEmpty());
+  EXPECT_THAT(aarch64_neoverse->target_features, Contains("+v9a"));
+
+  // RISC-V: ISA string (-march), profile (-march), CPU name (-mcpu), and tune
+  // (-mtune).
+  auto riscv_gc = compute({.target = "riscv64-unknown-linux-gnu",
+                           .target_cpu = "rv64gc",
+                           .target_cpu_tune = "spacemit-x60"});
+  ASSERT_THAT(riscv_gc, IsSuccess(_));
+  EXPECT_THAT(riscv_gc->tune_cpu, StrEq("spacemit-x60"));
+  EXPECT_THAT(riscv_gc->target_features, Contains("+m"));
+  EXPECT_THAT(riscv_gc->target_features, Contains("+a"));
+  EXPECT_THAT(riscv_gc->target_features, Contains("+f"));
+  EXPECT_THAT(riscv_gc->target_features, Contains("+d"));
+  EXPECT_THAT(riscv_gc->target_features, Contains("+c"));
+
+  auto riscv_profile = compute(
+      {.target = "riscv64-unknown-linux-gnu", .target_cpu = "rva22u64"});
+  ASSERT_THAT(riscv_profile, IsSuccess(_));
+  EXPECT_THAT(riscv_profile->target_features, Contains("+zba"));
+  EXPECT_THAT(riscv_profile->target_features, Contains("+zbb"));
+  EXPECT_THAT(riscv_profile->target_features, Contains("+zbs"));
+
+  auto riscv_cpu = compute(
+      {.target = "riscv64-unknown-linux-gnu", .target_cpu = "spacemit-x60"});
+  ASSERT_THAT(riscv_cpu, IsSuccess(_));
+  EXPECT_THAT(riscv_cpu->cpu, StrEq("spacemit-x60"));
+  EXPECT_THAT(riscv_cpu->tune_cpu, IsEmpty());
+  EXPECT_THAT(riscv_cpu->target_features, Contains("+v"));
+
+  // Host `native` resolution should canonicalize to a concrete CPU name for
+  // both target CPU and tune CPU.
+  std::string host_target = llvm::sys::getDefaultTargetTriple();
+  llvm::Triple host_triple(host_target);
+  if (host_triple.isX86() || host_triple.isAArch64()) {
+    std::string host_cpu = llvm::sys::getHostCPUName().str();
+    auto native_features = compute({.target = host_target,
+                                    .target_cpu = "native",
+                                    .target_cpu_tune = "native"});
+    ASSERT_THAT(native_features, IsSuccess(_));
+    EXPECT_THAT(native_features->cpu, StrEq(host_cpu));
+    EXPECT_THAT(native_features->tune_cpu, StrEq(host_cpu));
+    EXPECT_THAT(native_features->target_features, Not(IsEmpty()));
+  }
+
+  // `--target-cpu-features` across x86_64, AArch64, and RISC-V, including `+`,
+  // `-`, and bare feature names.
+  {
+    auto features = compute({.target = "x86_64-unknown-linux-gnu",
+                             .target_cpu = "x86-64-v3",
+                             .target_cpu_features = "-avx2,avx512f"});
+    ASSERT_THAT(features, IsSuccess(_));
+    EXPECT_THAT(features->cpu, StrEq("x86-64-v3"));
+    // Enabling `avx512f` after `-avx2` works in order and re-enables `avx2` as
+    // an implied prerequisite.
+    EXPECT_THAT(features->target_features, Contains("+avx512f"));
+    EXPECT_THAT(features->target_features, Contains("+avx2"));
+  }
+  {
+    auto features = compute({.target = "x86_64-unknown-linux-gnu",
+                             .target_cpu = "x86-64-v3",
+                             .target_cpu_features = "avx512f,-avx512f,-fma"});
+    ASSERT_THAT(features, IsSuccess(_));
+    EXPECT_THAT(features->target_features, Not(Contains("+avx512f")));
+    EXPECT_THAT(features->target_features, Not(Contains("+fma")));
+    EXPECT_THAT(features->target_features, Contains("+avx2"));
+  }
+  {
+    auto features = compute({.target = "aarch64-unknown-linux-gnu",
+                             .target_cpu = "armv8-a",
+                             .target_cpu_features = "sve,+lse,-crc"});
+    ASSERT_THAT(features, IsSuccess(_));
+    EXPECT_THAT(features->target_features, Contains("+sve"));
+    EXPECT_THAT(features->target_features, Contains("+lse"));
+    EXPECT_THAT(features->target_features, Not(Contains("+crc")));
+  }
+  {
+    auto features = compute({.target = "riscv64-unknown-linux-gnu",
+                             .target_cpu = "rv64gc",
+                             .target_cpu_features = "+zba,zbb,-m"});
+    ASSERT_THAT(features, IsSuccess(_));
+    EXPECT_THAT(features->target_features, Contains("+zba"));
+    EXPECT_THAT(features->target_features, Contains("+zbb"));
+    EXPECT_THAT(features->target_features, Not(Contains("+m")));
+  }
+
+  // Invalid target CPU, tune CPU, or target feature flags should return an
+  // error.
+  EXPECT_THAT(compute({.target = "x86_64-unknown-linux-gnu",
+                       .target_cpu = "invalid-cpu-name"}),
+              IsError(_));
+  EXPECT_THAT(compute({.target = "x86_64-unknown-linux-gnu",
+                       .target_cpu_tune = "invalid-cpu-name"}),
+              IsError(_));
+  EXPECT_THAT(compute({.target = "x86_64-unknown-linux-gnu",
+                       .target_cpu_features = "+not-a-feature"}),
+              IsError(_));
+  EXPECT_THAT(compute({.target = "riscv64-unknown-linux-gnu",
+                       .target_cpu_features = "+f,+zfinx"}),
+              IsError(_));
+}
+
 }  // namespace
 }  // namespace Carbon
diff --git a/toolchain/driver/clang_runtimes.cpp b/toolchain/driver/clang_runtimes.cpp
index 37255aa02baf..7b5966cba9b6 100644
--- a/toolchain/driver/clang_runtimes.cpp
+++ b/toolchain/driver/clang_runtimes.cpp
@@ -44,6 +44,36 @@
 
 namespace Carbon {
 
+ClangRuntimesBuilderBase::ClangRuntimesBuilderBase(
+    ClangRunner* clang, llvm::ThreadPoolInterface* threads,
+    const Runtimes::Cache::Features& features)
+    : clang_(clang),
+      vlog_stream_(clang_->vlog_stream_),
+      tasks_(*threads),
+      target_triple_(features.target),
+      target_flag_(llvm::formatv("--target={0}", target_triple_.str())),
+      result_(Error("Did not finish building the runtime!")) {
+  if (!features.cpu.empty() || !features.tune_cpu.empty() ||
+      !features.target_features.empty()) {
+    target_args_.push_back("--start-no-unused-arguments");
+    if (!features.cpu.empty()) {
+      target_args_.append({"-Xclang", "-target-cpu", "-Xclang", features.cpu,
+                           "-Xclangas", "-target-cpu", "-Xclangas",
+                           features.cpu});
+    }
+    if (!features.tune_cpu.empty()) {
+      target_args_.append(
+          {"-Xclang", "-tune-cpu", "-Xclang", features.tune_cpu});
+    }
+    for (const std::string& feature : features.target_features) {
+      target_args_.append({"-Xclang", "-target-feature", "-Xclang", feature,
+                           "-Xclangas", "-target-feature", "-Xclangas",
+                           feature});
+    }
+    target_args_.push_back("--end-no-unused-arguments");
+  }
+}
+
 auto ClangRuntimesBuilderBase::ArchiveBuilder::Setup(Latch::Handle latch_handle)
     -> void {
   // `NewArchiveMember` isn't default constructable unfortunately, so we have to
@@ -189,9 +219,12 @@ auto ClangRuntimesBuilderBase::ArchiveBuilder::CompileMember(
   }
 
   // Collect the additional required flags and dynamic flags for this builder.
+  args.push_back("-c");
+  args.push_back(builder_->target_flag_);
+  for (const std::string& target_arg : builder_->target_args_) {
+    args.push_back(target_arg);
+  }
   args.append({
-      "-c",
-      builder_->target_flag_,
       "-o",
       obj_path.native(),
       src_path.native(),
@@ -233,9 +266,9 @@ auto ClangRuntimesBuilderBase::ArchiveBuilder::CompileMember(
 template <Runtimes::Component Component>
   requires IsClangArchiveRuntimes<Component>
 ClangArchiveRuntimesBuilder<Component>::ClangArchiveRuntimesBuilder(
-    ClangRunner* clang, llvm::ThreadPoolInterface* threads,
-    llvm::Triple target_triple, Runtimes* runtimes)
-    : ClangRuntimesBuilderBase(clang, threads, std::move(target_triple)) {
+    ClangRunner* clang, llvm::ThreadPoolInterface* threads, Runtimes* runtimes,
+    const Runtimes::Cache::Features& features)
+    : ClangRuntimesBuilderBase(clang, threads, features) {
   // Ensure we're on a platform where we _can_ build a working runtime.
   if (target_triple_.isOSWindows()) {
     result_ =
@@ -391,9 +424,9 @@ auto ClangResourceDirBuilder::GetDarwinOsSuffix(llvm::Triple target_triple)
 }
 
 ClangResourceDirBuilder::ClangResourceDirBuilder(
-    ClangRunner* clang, llvm::ThreadPoolInterface* threads,
-    llvm::Triple target_triple, Runtimes* runtimes)
-    : ClangRuntimesBuilderBase(clang, threads, std::move(target_triple)),
+    ClangRunner* clang, llvm::ThreadPoolInterface* threads, Runtimes* runtimes,
+    const Runtimes::Cache::Features& features)
+    : ClangRuntimesBuilderBase(clang, threads, features),
       crt_begin_result_(Error("Never built CRT begin file!")),
       crt_end_result_(Error("Never built CRT end file!")) {
   // Ensure we're on a platform where we _can_ build a working runtime.
@@ -418,7 +451,7 @@ ClangResourceDirBuilder::ClangResourceDirBuilder(
   runtimes_builder_ = std::get<Runtimes::Builder>(std::move(build_dir));
   lib_path_ = std::filesystem::path("lib");
   std::filesystem::path builtins_name = "libclang_rt.builtins.a";
-  if (target_triple.isOSDarwin()) {
+  if (target_triple_.isOSDarwin()) {
     // Darwin targets don't use the full triple, and don't include the
     // architecture in the resource directory naming structure.
     //
@@ -554,6 +587,9 @@ auto ClangResourceDirBuilder::BuildCrtFile(llvm::StringRef src_file)
       "-w",
       target_flag_,
   };
+  for (const std::string& target_arg : target_args_) {
+    copts.push_back(target_arg);
+  }
   llvm::append_range(copts, RuntimesBuildInfo::CrtCopts);
   copts.append({
       "-c",
diff --git a/toolchain/driver/clang_runtimes.h b/toolchain/driver/clang_runtimes.h
index 8d8f53ebd9cc..5c20db30cbc4 100644
--- a/toolchain/driver/clang_runtimes.h
+++ b/toolchain/driver/clang_runtimes.h
@@ -54,13 +54,7 @@ class ClangRuntimesBuilderBase {
   // Both the `clang` runner and the `threads` need to outlive this object.
   ClangRuntimesBuilderBase(ClangRunner* clang,
                            llvm::ThreadPoolInterface* threads,
-                           llvm::Triple target_triple)
-      : clang_(clang),
-        vlog_stream_(clang_->vlog_stream_),
-        tasks_(*threads),
-        target_triple_(std::move(target_triple)),
-        target_flag_(llvm::formatv("--target={0}", target_triple_.str())),
-        result_(Error("Did not finish building the runtime!")) {}
+                           const Runtimes::Cache::Features& features);
 
   auto installation() -> const InstallPaths& { return *clang_->installation_; }
 
@@ -78,6 +72,7 @@ class ClangRuntimesBuilderBase {
 
   llvm::Triple target_triple_;
   std::string target_flag_;
+  llvm::SmallVector<std::string> target_args_;
 
   ErrorOr<std::filesystem::path> result_;
 
@@ -226,7 +221,8 @@ class ClangArchiveRuntimesBuilder : public ClangRuntimesBuilderBase {
   // they were already available, the call to `Wait` will not block.
   ClangArchiveRuntimesBuilder(ClangRunner* clang,
                               llvm::ThreadPoolInterface* threads,
-                              llvm::Triple target_triple, Runtimes* runtimes);
+                              Runtimes* runtimes,
+                              const Runtimes::Cache::Features& features);
 
  private:
   // Helpers to compute the list of source files and compile flags for a
@@ -280,7 +276,8 @@ class ClangResourceDirBuilder : public ClangRuntimesBuilderBase {
   // they were already available, the call to `Wait` will not block.
   ClangResourceDirBuilder(ClangRunner* clang,
                           llvm::ThreadPoolInterface* threads,
-                          llvm::Triple target_triple, Runtimes* runtimes);
+                          Runtimes* runtimes,
+                          const Runtimes::Cache::Features& features);
 
  private:
   friend class ClangResourceDirBuilderTestPeer;
diff --git a/toolchain/driver/clang_runtimes_test.cpp b/toolchain/driver/clang_runtimes_test.cpp
index e34f2e4d059a..077069febef6 100644
--- a/toolchain/driver/clang_runtimes_test.cpp
+++ b/toolchain/driver/clang_runtimes_test.cpp
@@ -27,7 +27,9 @@
 #include "testing/base/global_exe_path.h"
 #include "toolchain/base/install_paths.h"
 #include "toolchain/base/llvm_tools.h"
+#include "toolchain/diagnostics/null_diagnostics.h"
 #include "toolchain/driver/clang_runner.h"
+#include "toolchain/driver/codegen_options.h"
 #include "toolchain/driver/llvm_runner.h"
 #include "toolchain/driver/runtimes_cache.h"
 #include "tools/cpp/runfiles/runfiles.h"
@@ -270,8 +272,9 @@ class ClangRuntimesTest : public ::testing::Test {
 
   Runtimes::Cache runtimes_cache_ =
       *Runtimes::Cache::MakeSystem(install_paths_);
-  Runtimes::Cache::Features features = {.target = target_};
-  Runtimes runtimes_ = *runtimes_cache_.Lookup(features);
+  Runtimes::Cache::Features features_ = *runner_.ComputeRuntimesFeatures(
+      {.target = target_}, Diagnostics::NullConsumer());
+  Runtimes runtimes_ = *runtimes_cache_.Lookup(features_);
 
   // Note that for debugging it may be useful to replace this with a
   // single-threaded thread pool. However the test will be _much_ slower.
@@ -279,16 +282,28 @@ class ClangRuntimesTest : public ::testing::Test {
 };
 
 TEST_F(ClangRuntimesTest, ResourceDir) {
-  ClangResourceDirBuilder resource_dir_builder(&runner_, &threads_,
-                                               target_triple_, &runtimes_);
+  ClangResourceDirBuilder resource_dir_builder(&runner_, &threads_, &runtimes_,
+                                               features_);
   auto build_result = std::move(resource_dir_builder).Wait();
   ASSERT_TRUE(build_result.ok()) << build_result.error();
   TestResourceDir(std::move(*build_result));
+
+  if (target_triple_.isX86()) {
+    auto v3_features = *runner_.ComputeRuntimesFeatures(
+        {.target = target_, .target_cpu = "x86-64-v3"},
+        Diagnostics::NullConsumer());
+    auto v3_runtimes = *runtimes_cache_.Lookup(v3_features);
+    ClangResourceDirBuilder v3_builder(&runner_, &threads_, &v3_runtimes,
+                                       v3_features);
+    auto v3_result = std::move(v3_builder).Wait();
+    ASSERT_TRUE(v3_result.ok()) << v3_result.error();
+    TestResourceDir(std::move(*v3_result));
+  }
 }
 
 TEST_F(ClangRuntimesTest, Libunwind) {
-  LibunwindBuilder libunwind_builder(&runner_, &threads_, target_triple_,
-                                     &runtimes_);
+  LibunwindBuilder libunwind_builder(&runner_, &threads_, &runtimes_,
+                                     features_);
   auto build_result = std::move(libunwind_builder).Wait();
   ASSERT_TRUE(build_result.ok()) << build_result.error();
   std::filesystem::path runtimes_path = std::move(*build_result);
@@ -303,7 +318,7 @@ TEST_F(ClangRuntimesTest, Libunwind) {
 // sustainable way. Given that, we disable this test by default but include it
 // for debugging purposes.
 TEST_F(ClangRuntimesTest, DISABLED_Libcxx) {
-  LibcxxBuilder libcxx_builder(&runner_, &threads_, target_triple_, &runtimes_);
+  LibcxxBuilder libcxx_builder(&runner_, &threads_, &runtimes_, features_);
   auto build_result = std::move(libcxx_builder).Wait();
   ASSERT_TRUE(build_result.ok()) << build_result.error();
   std::filesystem::path runtimes_path = std::move(*build_result);
diff --git a/toolchain/driver/codegen_options.cpp b/toolchain/driver/codegen_options.cpp
index fdae3a6c4537..c0bcb46b5206 100644
--- a/toolchain/driver/codegen_options.cpp
+++ b/toolchain/driver/codegen_options.cpp
@@ -4,6 +4,15 @@
 
 #include "toolchain/driver/codegen_options.h"
 
+#include <string>
+
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/TargetParser/AArch64TargetParser.h"
+#include "llvm/TargetParser/RISCVISAInfo.h"
+#include "llvm/TargetParser/RISCVTargetParser.h"
+#include "llvm/TargetParser/Triple.h"
+
 namespace Carbon {
 
 auto CodegenOptions::Build(CommandLine::CommandBuilder& b) -> void {
@@ -23,6 +32,125 @@ https://clang.llvm.org/docs/CrossCompilation.html#target-triple
         arg_b.Default(host);
         arg_b.Set(&target);
       });
+
+  b.AddStringOption(
+      {
+          .name = "target-cpu",
+          .value_name = "CPU",
+          .help = R"""(
+Select a target CPU or architecture level.
+
+Accepts CPU names (such as `znver4`, `apple-m1`, `spacemit-x60`, or `native`) as
+well as architecture strings or profiles (such as `x86-64-v3`, `armv9-a`,
+`rv64gc`, or `rva22u64`). This corresponds to Clang's `-march` and `-mcpu`
+flags, selecting the appropriate underlying flag for the target architecture.
+)""",
+      },
+      [&](auto& arg_b) { arg_b.Set(&target_cpu); });
+
+  b.AddStringOption(
+      {
+          .name = "target-cpu-tune",
+          .value_name = "CPU",
+          .help = R"""(
+Select a target CPU to tune code generation for without enabling new
+instruction set extensions.
+
+Accepts CPU names (such as `znver4`, `apple-m1`, `spacemit-x60`, `generic`, or
+`native`). This corresponds to Clang's `-mtune` flag.
+)""",
+      },
+      [&](auto& arg_b) { arg_b.Set(&target_cpu_tune); });
+
+  b.AddStringOption(
+      {
+          .name = "target-cpu-features",
+          .value_name = "FEATURES",
+          .help = R"""(
+Select target CPU features to enable or disable.
+
+Accepts a comma-separated list of LLVM target feature names, optionally prefixed
+with `+` to enable or `-` to disable (such as `+avx2,-fma` or `sve,crc`). Bare
+feature names without a prefix are enabled.
+)""",
+      },
+      [&](auto& arg_b) { arg_b.Set(&target_cpu_features); });
+}
+
+static auto AppendTargetCpuClangArgs(llvm::StringRef target,
+                                     llvm::StringRef target_cpu,
+                                     llvm::SmallVectorImpl<std::string>& args)
+    -> void {
+  if (target_cpu.empty()) {
+    return;
+  }
+
+  llvm::Triple triple(target);
+  if (triple.isX86()) {
+    // On x86, Clang uses `-march=` for both microarchitecture levels (such as
+    // `x86-64-v3`) and specific CPUs (such as `znver4` or `native`), and does
+    // not support `-mcpu=`.
+    args.push_back(llvm::formatv("-march={0}", target_cpu).str());
+    return;
+  }
+
+  if (triple.isAArch64()) {
+    auto [base, _] = target_cpu.split('+');
+    bool is_arch =
+        llvm::AArch64::parseArch(base) != nullptr || base.starts_with("armv");
+    args.push_back(
+        llvm::formatv(is_arch ? "-march={0}" : "-mcpu={0}", target_cpu).str());
+    return;
+  }
+
+  if (triple.isRISCV()) {
+    auto isa_info = llvm::RISCVISAInfo::parseArchString(
+        target_cpu, /*EnableExperimentalExtension=*/true);
+    bool is_arch = static_cast<bool>(isa_info);
+    if (!isa_info) {
+      llvm::consumeError(isa_info.takeError());
+      is_arch =
+          !llvm::RISCV::parseCPU(target_cpu, triple.isRISCV64()) &&
+          (target_cpu.starts_with("rv32") || target_cpu.starts_with("rv64") ||
+           target_cpu.starts_with("rva") || target_cpu.starts_with("rvb") ||
+           target_cpu.starts_with("rvi") || target_cpu.starts_with("rvm"));
+    }
+    args.push_back(
+        llvm::formatv(is_arch ? "-march={0}" : "-mcpu={0}", target_cpu).str());
+    return;
+  }
+
+  args.push_back(llvm::formatv("-mcpu={0}", target_cpu).str());
+}
+
+auto CodegenOptions::AppendClangArgs(
+    llvm::SmallVectorImpl<std::string>& args) const -> void {
+  AppendTargetCpuClangArgs(target, target_cpu, args);
+  if (!target_cpu_tune.empty()) {
+    args.push_back(llvm::formatv("-mtune={0}", target_cpu_tune).str());
+  }
+  if (!target_cpu_features.empty()) {
+    llvm::SmallVector<llvm::StringRef> features;
+    target_cpu_features.split(features, ',', /*MaxSplit=*/-1,
+                              /*KeepEmpty=*/false);
+    for (llvm::StringRef feature : features) {
+      args.push_back("-Xclang");
+      args.push_back("-target-feature");
+      args.push_back("-Xclang");
+      if (feature.size() > 1 &&
+          (feature.starts_with('+') || feature.starts_with('-'))) {
+        args.push_back(feature.str());
+      } else {
+        args.push_back(llvm::formatv("+{0}", feature).str());
+      }
+    }
+  }
+}
+
+auto CodegenOptions::GetClangArgs() const -> llvm::SmallVector<std::string> {
+  llvm::SmallVector<std::string> args;
+  AppendClangArgs(args);
+  return args;
 }
 
 }  // namespace Carbon
diff --git a/toolchain/driver/codegen_options.h b/toolchain/driver/codegen_options.h
index 503258ec3d97..50707ca43723 100644
--- a/toolchain/driver/codegen_options.h
+++ b/toolchain/driver/codegen_options.h
@@ -5,7 +5,11 @@
 #ifndef CARBON_TOOLCHAIN_DRIVER_CODEGEN_OPTIONS_H_
 #define CARBON_TOOLCHAIN_DRIVER_CODEGEN_OPTIONS_H_
 
+#include <string>
+
 #include "common/command_line.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/TargetParser/Host.h"
 
@@ -17,8 +21,19 @@ namespace Carbon {
 struct CodegenOptions {
   auto Build(CommandLine::CommandBuilder& b) -> void;
 
+  // Appends the Clang driver flags corresponding to `target_cpu`,
+  // `target_cpu_tune`, and `target_cpu_features`.
+  auto AppendClangArgs(llvm::SmallVectorImpl<std::string>& args) const -> void;
+
+  // Returns the Clang driver flags corresponding to `target_cpu`,
+  // `target_cpu_tune`, and `target_cpu_features`.
+  auto GetClangArgs() const -> llvm::SmallVector<std::string>;
+
   std::string host = llvm::sys::getDefaultTargetTriple();
   llvm::StringRef target;
+  llvm::StringRef target_cpu;
+  llvm::StringRef target_cpu_tune;
+  llvm::StringRef target_cpu_features;
 };
 
 }  // namespace Carbon
diff --git a/toolchain/driver/compile_driver.cpp b/toolchain/driver/compile_driver.cpp
index a67c30b2e470..33f61319f07f 100644
--- a/toolchain/driver/compile_driver.cpp
+++ b/toolchain/driver/compile_driver.cpp
@@ -11,6 +11,7 @@
 #include <system_error>
 #include <utility>
 
+#include "clang/Basic/TargetOptions.h"
 #include "common/error.h"
 #include "common/ostream.h"
 #include "common/pretty_stack_trace_function.h"
@@ -18,6 +19,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
@@ -211,9 +213,21 @@ auto CompilationUnit::MakeTargetMachine(
   llvm::Triple target_triple(options_->codegen_options->target);
   module_->setTargetTriple(target_triple);
 
-  // TODO: Provide flags to control these.
-  constexpr llvm::StringLiteral CPU = "generic";
-  constexpr llvm::StringLiteral Features = "";
+  const auto& clang_target_opts = clang_invocation.getTargetOpts();
+  std::string features_str = llvm::join(clang_target_opts.Features, ",");
+
+  // LLVM's TargetMachine does not have a module-level TuneCPU setting; instead,
+  // target backends read the `"tune-cpu"` function attribute. Ignore Clang's
+  // implicit `"generic"` default on x86 unless `--target-cpu-tune` was set.
+  if (!clang_target_opts.TuneCPU.empty() &&
+      (!options_->codegen_options->target_cpu_tune.empty() ||
+       clang_target_opts.TuneCPU != "generic")) {
+    for (llvm::Function& fn : *module_) {
+      if (!fn.isDeclaration() && !fn.hasFnAttribute("tune-cpu")) {
+        fn.addFnAttr("tune-cpu", clang_target_opts.TuneCPU);
+      }
+    }
+  }
 
   const auto& codegen_opts = clang_invocation.getCodeGenOpts();
 
@@ -226,7 +240,8 @@ auto CompilationUnit::MakeTargetMachine(
   target_opts.DataSections = codegen_opts.DataSections;
   target_opts.UniqueSectionNames = codegen_opts.UniqueSectionNames;
   target_machine_.reset(target_->createTargetMachine(
-      target_triple, CPU, Features, target_opts, llvm::Reloc::PIC_));
+      target_triple, clang_target_opts.CPU, features_str, target_opts,
+      llvm::Reloc::PIC_));
 }
 
 auto CompilationUnit::RunOptimize(
diff --git a/toolchain/driver/compile_options.cpp b/toolchain/driver/compile_options.cpp
index ca4eef2a1a62..837452d2be9a 100644
--- a/toolchain/driver/compile_options.cpp
+++ b/toolchain/driver/compile_options.cpp
@@ -497,13 +497,19 @@ auto CompileOptions::BuildClangInvocation(DriverEnv& driver_env)
     -> ErrorOr<std::shared_ptr<clang::CompilerInvocation>> {
   // TODO: Move this into `BuildClangInvocation` when it can accept an
   // optimization level.
-  llvm::SmallVector<llvm::StringRef> all_clang_args = {
-      // Propagate our optimization level to Clang as a default. This can be
-      // overridden by Clang arguments, but doing so will only have an effect
-      // if those arguments affect Clang's IR, not its pass pipeline.
-      CompileOptions::GetClangOptimizationFlag(opt_level),
-  };
-  all_clang_args.append(clang_args);
+  llvm::SmallVector<std::string> codegen_clang_args =
+      codegen_options->GetClangArgs();
+  llvm::SmallVector<llvm::StringRef> all_clang_args;
+  all_clang_args.reserve(1 + clang_args.size() + codegen_clang_args.size());
+  // Propagate our optimization level and codegen options to Clang as defaults.
+  // These can be overridden by Clang arguments, though optimization flags will
+  // only have an effect if those arguments affect Clang's IR, not its pass
+  // pipeline.
+  all_clang_args.push_back(CompileOptions::GetClangOptimizationFlag(opt_level));
+  for (llvm::StringRef arg : codegen_clang_args) {
+    all_clang_args.push_back(arg);
+  }
+  all_clang_args.append(clang_args.begin(), clang_args.end());
   auto clang_invocation = Carbon::BuildClangInvocation(
       *driver_env.consumer, driver_env.fs, *driver_env.installation,
       codegen_options->target, all_clang_args);
diff --git a/toolchain/driver/config_subcommand.cpp b/toolchain/driver/config_subcommand.cpp
index 3e8fa2243ea8..76bceedc125f 100644
--- a/toolchain/driver/config_subcommand.cpp
+++ b/toolchain/driver/config_subcommand.cpp
@@ -75,14 +75,22 @@ struct ConfigDataEntry {
 // If there are any errors setting up Clang, this will diagnose them using
 // `driver_env.consumer` and return `false`. If successful, returns `true`.
 static auto ComputeClangConfig(DriverEnv& driver_env,
-                               llvm::StringRef target_str,
+                               const CodegenOptions& codegen_options,
                                llvm::SmallVectorImpl<ConfigDataEntry>& data)
     -> bool {
+  llvm::SmallVector<std::string> codegen_clang_args =
+      codegen_options.GetClangArgs();
+  llvm::SmallVector<llvm::StringRef> extra_args(codegen_clang_args.begin(),
+                                                codegen_clang_args.end());
+
   // Build a library invocation of Clang in order to query its header search
   // paths.
-  std::shared_ptr clang_invocation =
-      BuildClangInvocation(*driver_env.consumer, driver_env.fs,
-                           *driver_env.installation, target_str, {});
+  std::shared_ptr clang_invocation = BuildClangInvocation(
+      *driver_env.consumer, driver_env.fs, *driver_env.installation,
+      codegen_options.target, extra_args);
+  if (!clang_invocation) {
+    return false;
+  }
   clang_invocation->getFrontendOpts().DisableFree = false;
 
   // Setup up a driver-style diagnostic engine for the compiler invocation and
@@ -106,7 +114,8 @@ static auto ComputeClangConfig(DriverEnv& driver_env,
     CARBON_DIAGNOSTIC(ConfigFailedToSetupTarget, Error,
                       "unable to setup the requested target `{0}`",
                       std::string);
-    driver_env.emitter.Emit(ConfigFailedToSetupTarget, target_str.str());
+    driver_env.emitter.Emit(ConfigFailedToSetupTarget,
+                            codegen_options.target.str());
     return false;
   }
 
@@ -215,8 +224,7 @@ auto ConfigSubcommand::Run(DriverEnv& driver_env) -> DriverResult {
 
   // Compute and print Clang's config entries if we can. This will have been
   // diagnosed while computing, so just track if we hit errors.
-  result &=
-      ComputeClangConfig(driver_env, options_.codegen_options.target, data);
+  result &= ComputeClangConfig(driver_env, options_.codegen_options, data);
 
   llvm::sort(data, [](const ConfigDataEntry& lhs, const ConfigDataEntry& rhs) {
     return lhs.key < rhs.key;
diff --git a/toolchain/driver/driver_test.cpp b/toolchain/driver/driver_test.cpp
index 9e30f71370f5..f5aa63914a0c 100644
--- a/toolchain/driver/driver_test.cpp
+++ b/toolchain/driver/driver_test.cpp
@@ -22,6 +22,8 @@
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/JSON.h"
+#include "llvm/TargetParser/Host.h"
+#include "llvm/TargetParser/Triple.h"
 #include "testing/base/capture_std_streams.h"
 #include "testing/base/file_helpers.h"
 #include "testing/base/global_exe_path.h"
@@ -369,5 +371,224 @@ fn Run() {
   EXPECT_TRUE(result->getBinary()->isObject());
 }
 
+TEST_F(DriverTest, TargetCpu) {
+  MakeTestFile("fn Run() {}", "test.carbon");
+
+  struct TargetCpuCase {
+    llvm::StringRef target;
+    llvm::StringRef cpu = "";
+    llvm::StringRef tune_cpu = "";
+    llvm::StringRef features = "";
+  };
+  TargetCpuCase compile_cases[] = {
+      {.target = "x86_64-unknown-linux-gnu", .cpu = "x86-64-v3"},
+      {.target = "x86_64-unknown-linux-gnu",
+       .cpu = "x86-64-v3",
+       .tune_cpu = "znver4"},
+      {.target = "x86_64-unknown-linux-gnu", .cpu = "znver4"},
+      {.target = "x86_64-unknown-linux-gnu", .tune_cpu = "znver4"},
+      {.target = "x86_64-unknown-linux-gnu",
+       .cpu = "x86-64-v2",
+       .tune_cpu = "znver4",
+       .features = "+avx2,-fma,bmi2"},
+      {.target = "aarch64-unknown-linux-gnu", .cpu = "armv9-a"},
+      {.target = "aarch64-unknown-linux-gnu",
+       .cpu = "armv9-a",
+       .tune_cpu = "neoverse-v2"},
+      {.target = "aarch64-unknown-linux-gnu", .cpu = "neoverse-v2"},
+      {.target = "aarch64-unknown-linux-gnu", .tune_cpu = "neoverse-v2"},
+      {.target = "aarch64-unknown-linux-gnu",
+       .cpu = "armv8.2-a",
+       .features = "sve,-crc"},
+  };
+
+  for (const auto& tc : compile_cases) {
+    SCOPED_TRACE(llvm::formatv("target={0}, cpu={1}, tune={2}, features={3}",
+                               tc.target, tc.cpu, tc.tune_cpu, tc.features)
+                     .str());
+    std::string target_arg = llvm::formatv("--target={0}", tc.target).str();
+    std::string cpu_arg = llvm::formatv("--target-cpu={0}", tc.cpu).str();
+    std::string tune_arg =
+        llvm::formatv("--target-cpu-tune={0}", tc.tune_cpu).str();
+    std::string features_arg =
+        llvm::formatv("--target-cpu-features={0}", tc.features).str();
+    llvm::SmallVector<llvm::StringRef> args = {"compile", "--no-prelude-import",
+                                               "--output=-", target_arg};
+    if (!tc.cpu.empty()) {
+      args.push_back(cpu_arg);
+    }
+    if (!tc.tune_cpu.empty()) {
+      args.push_back(tune_arg);
+    }
+    if (!tc.features.empty()) {
+      args.push_back(features_arg);
+    }
+    args.push_back("test.carbon");
+    EXPECT_TRUE(driver_.RunCommand(args).success)
+        << test_error_stream_.TakeStr();
+    EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
+    EXPECT_THAT(test_output_stream_.TakeStr(), HasSubstr("main:"));
+  }
+
+  // Test `native` on the host target.
+  std::string host_target = llvm::sys::getDefaultTargetTriple();
+  llvm::Triple host_triple(host_target);
+  if (host_triple.isX86() || host_triple.isAArch64()) {
+    EXPECT_TRUE(driver_
+                    .RunCommand({"compile", "--no-prelude-import", "--output=-",
+                                 "--target-cpu=native",
+                                 "--target-cpu-tune=native", "test.carbon"})
+                    .success)
+        << test_error_stream_.TakeStr();
+    EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
+    EXPECT_THAT(test_output_stream_.TakeStr(), HasSubstr("main:"));
+  }
+
+  // Invalid target CPU, tune CPU, or target features should fail cleanly with a
+  // diagnostic across `compile`, `link`, and `build-runtimes`.
+  for (llvm::StringRef target :
+       {"x86_64-unknown-linux-gnu", "aarch64-unknown-linux-gnu"}) {
+    std::string target_arg = llvm::formatv("--target={0}", target).str();
+    EXPECT_FALSE(
+        driver_
+            .RunCommand({"compile", "--no-prelude-import", "--output=-",
+                         target_arg, "--target-cpu=not-a-valid-cpu",
+                         "test.carbon"})
+            .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("not-a-valid-cpu"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(
+        driver_
+            .RunCommand({"compile", "--no-prelude-import", "--output=-",
+                         target_arg, "--target-cpu-tune=not-a-valid-tune-cpu",
+                         "test.carbon"})
+            .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(),
+                HasSubstr("not-a-valid-tune-cpu"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(
+        driver_
+            .RunCommand({"compile", "--no-prelude-import", "--output=-",
+                         target_arg, "--target-cpu-features=+not-a-feature",
+                         "test.carbon"})
+            .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("+not-a-feature"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(
+        driver_
+            .RunCommand({"--no-build-runtimes", "link", "--output=out",
+                         target_arg, "--target-cpu=not-a-valid-cpu", "test.o"})
+            .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("not-a-valid-cpu"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(
+        driver_
+            .RunCommand({"--no-build-runtimes", "link", "--output=out",
+                         target_arg, "--target-cpu-features=+not-a-feature",
+                         "test.o"})
+            .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("+not-a-feature"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(driver_
+                     .RunCommand({"build-runtimes", target_arg,
+                                  "--target-cpu=not-a-valid-cpu"})
+                     .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("not-a-valid-cpu"));
+    test_output_stream_.TakeStr();
+
+    EXPECT_FALSE(driver_
+                     .RunCommand({"build-runtimes", target_arg,
+                                  "--target-cpu-features=+not-a-feature"})
+                     .success);
+    EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("+not-a-feature"));
+    test_output_stream_.TakeStr();
+  }
+
+  // Test RISC-V `--target-cpu`, `--target-cpu-tune`, and
+  // `--target-cpu-features` mapping and Clang target validation via `config`
+  // (since the RISC-V LLVM codegen backend is not linked by default).
+  auto cleanup = ScopedTempWorkingDir();
+  MakeTestFile("fn Run() {}", "host_test.carbon");
+  if (host_triple.isX86() || host_triple.isAArch64()) {
+    llvm::StringRef host_cpu = host_triple.isX86() ? "x86-64-v3" : "armv8.2-a";
+    llvm::StringRef host_tune = host_triple.isX86() ? "znver4" : "neoverse-v2";
+    llvm::StringRef host_feature = host_triple.isX86() ? "+bmi2" : "+lse";
+    std::string cpu_arg = llvm::formatv("--target-cpu={0}", host_cpu).str();
+    std::string tune_arg =
+        llvm::formatv("--target-cpu-tune={0}", host_tune).str();
+    std::string feature_arg =
+        llvm::formatv("--target-cpu-features={0}", host_feature).str();
+
+    ASSERT_TRUE(driver_
+                    .RunCommand({"compile", "--no-prelude-import", cpu_arg,
+                                 tune_arg, feature_arg, "host_test.carbon"})
+                    .success)
+        << test_error_stream_.TakeStr();
+    EXPECT_TRUE(driver_
+                    .RunCommand({"--no-build-runtimes", "link",
+                                 "--output=host_test_linked", cpu_arg, tune_arg,
+                                 feature_arg, "host_test.o", "--", "-lc"})
+                    .success)
+        << test_error_stream_.TakeStr();
+    EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
+
+    // Also verify `build` with `--target-cpu` and a compile-only `--clang-arg`
+    // (such as `-fsanitize=address`, which would fail linking if forwarded to
+    // the link step without sanitizer runtimes).
+    EXPECT_TRUE(
+        driver_
+            .RunCommand({"--no-build-runtimes", "build", "--no-use-temp-dir",
+                         "--no-prelude-import",
+                         "--clang-arg=-fsanitize=address", cpu_arg, tune_arg,
+                         feature_arg, "host_test.carbon", "--", "--", "-lc"})
+            .success)
+        << test_error_stream_.TakeStr();
+    EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
+  }
+
+  for (llvm::StringRef riscv_cpu : {"rv64gc", "rva22u64", "spacemit-x60"}) {
+    SCOPED_TRACE(riscv_cpu);
+    std::string cpu_arg = llvm::formatv("--target-cpu={0}", riscv_cpu).str();
+    EXPECT_TRUE(driver_
+                    .RunCommand({"config", "--json",
+                                 "--target=riscv64-unknown-linux-gnu", cpu_arg,
+                                 "--target-cpu-tune=spacemit-x60",
+                                 "--target-cpu-features=+zba,-m"})
+                    .success)
+        << test_error_stream_.TakeStr();
+    EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
+    test_output_stream_.TakeStr();
+  }
+  EXPECT_FALSE(
+      driver_
+          .RunCommand({"config", "--json", "--target=riscv64-unknown-linux-gnu",
+                       "--target-cpu=not-a-valid-cpu"})
+          .success);
+  EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("not-a-valid-cpu"));
+  test_output_stream_.TakeStr();
+
+  EXPECT_FALSE(
+      driver_
+          .RunCommand({"config", "--json", "--target=riscv64-unknown-linux-gnu",
+                       "--target-cpu-tune=not-a-valid-tune-cpu"})
+          .success);
+  EXPECT_THAT(test_error_stream_.TakeStr(), HasSubstr("not-a-valid-tune-cpu"));
+  test_output_stream_.TakeStr();
+
+  EXPECT_FALSE(
+      driver_
+          .RunCommand({"config", "--json", "--target=riscv64-unknown-linux-gnu",
+                       "--target-cpu-features=+f,+zfinx"})
+          .success);
+  EXPECT_THAT(test_error_stream_.TakeStr(),
+              HasSubstr("invalid feature combination"));
+  test_output_stream_.TakeStr();
+}
+
 }  // namespace
 }  // namespace Carbon
diff --git a/toolchain/driver/link_driver.cpp b/toolchain/driver/link_driver.cpp
index 3979aa2d2cdd..0b558d565cc8 100644
--- a/toolchain/driver/link_driver.cpp
+++ b/toolchain/driver/link_driver.cpp
@@ -67,10 +67,19 @@ auto LinkDriver::Link(DriverEnv& driver_env) -> DriverResult {
   // We link using a C++ mode of the driver.
   clang_args.push_back("--driver-mode=g++");
 
-  // Pass the target down to Clang to pick up the correct defaults.
+  // Pass the target and codegen flags down to Clang as defaults.
   std::string target_arg =
       llvm::formatv("--target={0}", options_->codegen_options->target).str();
   clang_args.push_back(target_arg);
+  llvm::SmallVector<std::string> codegen_clang_args =
+      options_->codegen_options->GetClangArgs();
+  if (!codegen_clang_args.empty()) {
+    clang_args.push_back("--start-no-unused-arguments");
+    for (llvm::StringRef arg : codegen_clang_args) {
+      clang_args.push_back(arg);
+    }
+    clang_args.push_back("--end-no-unused-arguments");
+  }
 
   if (!options_->output_filename.empty()) {
     clang_args.push_back("-o");
@@ -92,6 +101,15 @@ auto LinkDriver::Link(DriverEnv& driver_env) -> DriverResult {
     return {.success = false};
   }
 
+  ClangRunner runner(driver_env.installation, driver_env.fs,
+                     driver_env.vlog_stream);
+
+  auto features = runner.ComputeRuntimesFeatures(*options_->codegen_options,
+                                                 *driver_env.consumer);
+  if (!features.ok()) {
+    return {.success = false};
+  }
+
   // Find or build the Carbon Core runtimes for linking the prelude into the
   // binary.
   bool include_prelude = false;
@@ -111,9 +129,7 @@ auto LinkDriver::Link(DriverEnv& driver_env) -> DriverResult {
       runtimes_path = driver_env.prebuilt_runtimes->base_path();
       include_prelude = true;
     } else if (driver_env.build_runtimes_on_demand) {
-      Runtimes::Cache::Features features = {
-          .target = options_->codegen_options->target.str()};
-      auto runtimes_or_error = driver_env.runtimes_cache.Lookup(features);
+      auto runtimes_or_error = driver_env.runtimes_cache.Lookup(*features);
       CARBON_CHECK(runtimes_or_error.ok(), "Runtimes cache lookup failed: {}",
                    runtimes_or_error.error().message());
       auto runtimes = std::move(*runtimes_or_error);
@@ -171,8 +187,6 @@ auto LinkDriver::Link(DriverEnv& driver_env) -> DriverResult {
   clang_args.append(options_->object_filenames.begin(),
                     options_->object_filenames.end());
 
-  ClangRunner runner(driver_env.installation, driver_env.fs,
-                     driver_env.vlog_stream);
   ErrorOr<bool> run_result =
       driver_env.prebuilt_runtimes
           ? runner.RunWithPrebuiltRuntimes(clang_args,
@@ -180,7 +194,8 @@ auto LinkDriver::Link(DriverEnv& driver_env) -> DriverResult {
                                            driver_env.enable_leaking)
       : driver_env.build_runtimes_on_demand
           ? runner.Run(clang_args, driver_env.runtimes_cache,
-                       *driver_env.thread_pool, driver_env.enable_leaking)
+                       *driver_env.thread_pool, driver_env.enable_leaking,
+                       *std::move(features))
           : runner.RunWithNoRuntimes(clang_args, driver_env.enable_leaking);
 
   if (!run_result.ok()) {
diff --git a/toolchain/driver/runtimes_cache.cpp b/toolchain/driver/runtimes_cache.cpp
index adbfc93cca50..1135d1d19133 100644
--- a/toolchain/driver/runtimes_cache.cpp
+++ b/toolchain/driver/runtimes_cache.cpp
@@ -251,12 +251,21 @@ auto Runtimes::Cache::Lookup(const Features& features) -> ErrorOr<Runtimes> {
   // within the cache.
 
   llvm::SHA256 entry_hasher;
+  auto update_with_separator = [&](llvm::StringRef str) {
+    entry_hasher.update(str);
+    entry_hasher.update(llvm::ArrayRef<uint8_t>{0});
+  };
   // First incorporate our cache key that comes from the installation's digest.
   // This ensures we don't share a cache entry with any other Carbon
   // installations using different inputs.
-  entry_hasher.update(cache_key_);
+  update_with_separator(cache_key_);
   // Then incorporate the specific features that are enabled in this entry.
-  entry_hasher.update(features.target);
+  update_with_separator(features.target);
+  update_with_separator(features.cpu);
+  update_with_separator(features.tune_cpu);
+  for (llvm::StringRef feature : features.target_features) {
+    update_with_separator(feature);
+  }
 
   std::array<uint8_t, 32> entry_digest = entry_hasher.final();
   std::filesystem::path entry_path =
diff --git a/toolchain/driver/runtimes_cache.h b/toolchain/driver/runtimes_cache.h
index b2710b9ab81e..a4a6cbde2b59 100644
--- a/toolchain/driver/runtimes_cache.h
+++ b/toolchain/driver/runtimes_cache.h
@@ -7,6 +7,7 @@
 
 #include <chrono>
 #include <filesystem>
+#include <string>
 #include <utility>
 
 #include "common/check.h"
@@ -14,6 +15,7 @@
 #include "common/filesystem.h"
 #include "common/ostream.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "toolchain/base/install_paths.h"
 
@@ -234,9 +236,20 @@ class Runtimes::Cache {
   // The features of a cached runtimes directory.
   //
   // TODO: Add support for more build flags that we want to enable when building
-  // runtimes such as sanitizers and CPU-specific optimizations.
+  // runtimes such as sanitizers.
   struct Features {
+    // The target triple to build runtimes for.
     std::string target;
+
+    // The canonical target CPU name (from `clang::TargetOptions::CPU`).
+    std::string cpu = {};
+
+    // The canonical tune CPU name (from `clang::TargetOptions::TuneCPU`).
+    std::string tune_cpu = {};
+
+    // The canonical sorted target features (`+<feature>` / `-<feature>` from
+    // `clang::TargetOptions::Features`).
+    llvm::SmallVector<std::string> target_features = {};
   };
 
   Cache() = default;
diff --git a/toolchain/driver/runtimes_cache_test.cpp b/toolchain/driver/runtimes_cache_test.cpp
index d14d02b7f44b..a5cbe3118c97 100644
--- a/toolchain/driver/runtimes_cache_test.cpp
+++ b/toolchain/driver/runtimes_cache_test.cpp
@@ -547,6 +547,51 @@ TEST_F(RuntimesCacheTest, Lookup) {
               Eq(runtimes.base_dir().Stat()->unix_inode()));
 }
 
+TEST_F(RuntimesCacheTest, LookupTargetCpuFeatures) {
+  Runtimes::Cache::Features base_features = {
+      .target = "x86_64-unknown-linux-gnu",
+      .cpu = "x86-64-v3",
+      .tune_cpu = "znver4",
+      .target_features = {"+avx2", "+bmi2"},
+  };
+  auto base_runtimes = *cache_.Lookup(base_features);
+
+  // Looking up identical features should return the same cache directory.
+  auto same_runtimes = *cache_.Lookup(base_features);
+  EXPECT_THAT(same_runtimes.base_path(), Eq(base_runtimes.base_path()));
+
+  // Changing `cpu` should produce a distinct cache directory.
+  auto diff_cpu = base_features;
+  diff_cpu.cpu = "x86-64-v4";
+  EXPECT_THAT(cache_.Lookup(diff_cpu)->base_path(),
+              Ne(base_runtimes.base_path()));
+
+  // Changing `tune_cpu` should produce a distinct cache directory.
+  auto diff_tune = base_features;
+  diff_tune.tune_cpu = "skylake";
+  EXPECT_THAT(cache_.Lookup(diff_tune)->base_path(),
+              Ne(base_runtimes.base_path()));
+
+  // Changing `target_features` should produce a distinct cache directory.
+  auto diff_features = base_features;
+  diff_features.target_features = {"+avx2"};
+  EXPECT_THAT(cache_.Lookup(diff_features)->base_path(),
+              Ne(base_runtimes.base_path()));
+
+  // Shifting characters across field boundaries should not collide.
+  auto boundary1 = *cache_.Lookup({
+      .target = "x86_64-unknown-linux-gnu",
+      .cpu = "ab",
+      .tune_cpu = "c",
+  });
+  auto boundary2 = *cache_.Lookup({
+      .target = "x86_64-unknown-linux-gnu",
+      .cpu = "a",
+      .tune_cpu = "bc",
+  });
+  EXPECT_THAT(boundary1.base_path(), Ne(boundary2.base_path()));
+}
+
 TEST_F(RuntimesCacheTest, LookupFailsIfCannotCreateDir) {
   // Create a read-only directory with the cache in it to cause failures.
   std::filesystem::path ro_cache_path = tmp_dir_.path() / "ro_cache";
diff --git a/toolchain/driver/testdata/compile/fail_target_cpu.carbon b/toolchain/driver/testdata/compile/fail_target_cpu.carbon
new file mode 100644
index 000000000000..6d3ff9accde9
--- /dev/null
+++ b/toolchain/driver/testdata/compile/fail_target_cpu.carbon
@@ -0,0 +1,17 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// ARGS: --include-diagnostic-kind compile --target=x86_64-unknown-linux-gnu --target-cpu=not-a-valid-cpu --target-cpu-features=+not-a-feature foo.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/driver/testdata/compile/fail_target_cpu.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/driver/testdata/compile/fail_target_cpu.carbon
+// CHECK:STDERR: error: unknown target CPU 'not-a-valid-cpu' [CppInteropDriverError]
+// CHECK:STDERR:
+// CHECK:STDERR: error: unsupported argument '+not-a-feature' to option '-target-feature' [CppInteropDriverError]
+// CHECK:STDERR:
+
+// --- foo.carbon
diff --git a/toolchain/driver/testdata/compile/target_cpu.carbon b/toolchain/driver/testdata/compile/target_cpu.carbon
new file mode 100644
index 000000000000..a569b7a0c62b
--- /dev/null
+++ b/toolchain/driver/testdata/compile/target_cpu.carbon
@@ -0,0 +1,202 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// ARGS: compile --optimize=speed foo.carbon --target=x86_64-unknown-linux-gnu --target-cpu=x86-64-v2 --target-cpu-tune=znver4 --target-cpu-features=+avx2,-popcnt --clang-arg=-mlzcnt --phase=optimize --dump-llvm-ir --exclude-dump-file-prefix=%{core}
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/driver/testdata/compile/target_cpu.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/driver/testdata/compile/target_cpu.carbon
+
+// --- foo.carbon
+
+import Cpp inline '''
+#ifndef __AVX2__
+#error "__AVX2__ should be defined via --target-cpu-features=+avx2"
+#endif
+#ifdef __POPCNT__
+#error "__POPCNT__ should be disabled via --target-cpu-features=-popcnt"
+#endif
+#ifndef __LAHF_SAHF__
+#error "__LAHF_SAHF__ should be defined via --target-cpu=x86-64-v2"
+#endif
+#ifndef __LZCNT__
+#error "__LZCNT__ should be defined via --clang-arg=-mlzcnt"
+#endif
+''';
+
+fn VectorizedWithAvx2(a: array(i32, 65536)*) {
+  // With --target-cpu-features=+avx2, this loop should vectorize using
+  // 256-bit (<8 x i32>) vectors instead of baseline 128-bit (<4 x i32>).
+  var n: i32 = 0;
+  while (n < 65536) {
+    (*a)[n] *= 2;
+    ++n;
+  }
+}
+
+// CHECK:STDOUT: ; ---
+// CHECK:STDOUT: ; ModuleID = 'foo.carbon'
+// CHECK:STDOUT: source_filename = "foo.carbon"
+// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nofree norecurse nosync nounwind memory(argmem: readwrite)
+// CHECK:STDOUT: define void @_CVectorizedWithAvx2.Main(ptr nofree captures(none) %a) local_unnamed_addr #0 !dbg !8 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   br label %vector.body, !dbg !13
+// CHECK:STDOUT:
+// CHECK:STDOUT: vector.body:                                      ; preds = %vector.body, %entry
+// CHECK:STDOUT:   %index = phi i64 [ 0, %entry ], [ %index.next.3, %vector.body ], !dbg !80
+// CHECK:STDOUT:   %0 = getelementptr inbounds nuw [4 x i8], ptr %a, i64 %index, !dbg !18
+// CHECK:STDOUT:   %1 = getelementptr inbounds nuw i8, ptr %0, i64 32, !dbg !18
+// CHECK:STDOUT:   %2 = getelementptr inbounds nuw i8, ptr %0, i64 64, !dbg !18
+// CHECK:STDOUT:   %3 = getelementptr inbounds nuw i8, ptr %0, i64 96, !dbg !18
+// CHECK:STDOUT:   %wide.load = load <8 x i32>, ptr %0, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load5 = load <8 x i32>, ptr %1, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load6 = load <8 x i32>, ptr %2, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load7 = load <8 x i32>, ptr %3, align 4, !dbg !18
+// CHECK:STDOUT:   %4 = shl <8 x i32> %wide.load, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %5 = shl <8 x i32> %wide.load5, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %6 = shl <8 x i32> %wide.load6, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %7 = shl <8 x i32> %wide.load7, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %4, ptr %0, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %5, ptr %1, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %6, ptr %2, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %7, ptr %3, align 4, !dbg !18
+// CHECK:STDOUT:   %8 = getelementptr inbounds nuw [4 x i8], ptr %a, i64 %index, !dbg !18
+// CHECK:STDOUT:   %9 = getelementptr inbounds nuw i8, ptr %8, i64 128, !dbg !18
+// CHECK:STDOUT:   %10 = getelementptr inbounds nuw i8, ptr %8, i64 160, !dbg !18
+// CHECK:STDOUT:   %11 = getelementptr inbounds nuw i8, ptr %8, i64 192, !dbg !18
+// CHECK:STDOUT:   %12 = getelementptr inbounds nuw i8, ptr %8, i64 224, !dbg !18
+// CHECK:STDOUT:   %wide.load.1 = load <8 x i32>, ptr %9, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load5.1 = load <8 x i32>, ptr %10, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load6.1 = load <8 x i32>, ptr %11, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load7.1 = load <8 x i32>, ptr %12, align 4, !dbg !18
+// CHECK:STDOUT:   %13 = shl <8 x i32> %wide.load.1, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %14 = shl <8 x i32> %wide.load5.1, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %15 = shl <8 x i32> %wide.load6.1, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %16 = shl <8 x i32> %wide.load7.1, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %13, ptr %9, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %14, ptr %10, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %15, ptr %11, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %16, ptr %12, align 4, !dbg !18
+// CHECK:STDOUT:   %17 = getelementptr inbounds nuw [4 x i8], ptr %a, i64 %index, !dbg !18
+// CHECK:STDOUT:   %18 = getelementptr inbounds nuw i8, ptr %17, i64 256, !dbg !18
+// CHECK:STDOUT:   %19 = getelementptr inbounds nuw i8, ptr %17, i64 288, !dbg !18
+// CHECK:STDOUT:   %20 = getelementptr inbounds nuw i8, ptr %17, i64 320, !dbg !18
+// CHECK:STDOUT:   %21 = getelementptr inbounds nuw i8, ptr %17, i64 352, !dbg !18
+// CHECK:STDOUT:   %wide.load.2 = load <8 x i32>, ptr %18, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load5.2 = load <8 x i32>, ptr %19, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load6.2 = load <8 x i32>, ptr %20, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load7.2 = load <8 x i32>, ptr %21, align 4, !dbg !18
+// CHECK:STDOUT:   %22 = shl <8 x i32> %wide.load.2, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %23 = shl <8 x i32> %wide.load5.2, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %24 = shl <8 x i32> %wide.load6.2, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %25 = shl <8 x i32> %wide.load7.2, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %22, ptr %18, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %23, ptr %19, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %24, ptr %20, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %25, ptr %21, align 4, !dbg !18
+// CHECK:STDOUT:   %26 = getelementptr inbounds nuw [4 x i8], ptr %a, i64 %index, !dbg !18
+// CHECK:STDOUT:   %27 = getelementptr inbounds nuw i8, ptr %26, i64 384, !dbg !18
+// CHECK:STDOUT:   %28 = getelementptr inbounds nuw i8, ptr %26, i64 416, !dbg !18
+// CHECK:STDOUT:   %29 = getelementptr inbounds nuw i8, ptr %26, i64 448, !dbg !18
+// CHECK:STDOUT:   %30 = getelementptr inbounds nuw i8, ptr %26, i64 480, !dbg !18
+// CHECK:STDOUT:   %wide.load.3 = load <8 x i32>, ptr %27, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load5.3 = load <8 x i32>, ptr %28, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load6.3 = load <8 x i32>, ptr %29, align 4, !dbg !18
+// CHECK:STDOUT:   %wide.load7.3 = load <8 x i32>, ptr %30, align 4, !dbg !18
+// CHECK:STDOUT:   %31 = shl <8 x i32> %wide.load.3, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %32 = shl <8 x i32> %wide.load5.3, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %33 = shl <8 x i32> %wide.load6.3, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   %34 = shl <8 x i32> %wide.load7.3, splat (i32 1), !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %31, ptr %27, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %32, ptr %28, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %33, ptr %29, align 4, !dbg !18
+// CHECK:STDOUT:   store <8 x i32> %34, ptr %30, align 4, !dbg !18
+// CHECK:STDOUT:   %index.next.3 = add nuw nsw i64 %index, 128, !dbg !80
+// CHECK:STDOUT:   %35 = icmp eq i64 %index.next.3, 65536, !dbg !13
+// CHECK:STDOUT:   br i1 %35, label %while.done, label %vector.body, !dbg !13, !llvm.loop !88
+// CHECK:STDOUT:
+// CHECK:STDOUT: while.done:                                       ; preds = %vector.body
+// CHECK:STDOUT:   ret void, !dbg !22
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; uselistorder directives
+// CHECK:STDOUT:   uselistorder i64 %index, { 3, 0, 1, 2, 4 }
+// CHECK:STDOUT:   uselistorder ptr %0, { 3, 4, 0, 1, 2 }
+// CHECK:STDOUT:   uselistorder ptr %1, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %2, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %3, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %10, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %11, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %12, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %19, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %20, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %21, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %28, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %29, { 1, 0 }
+// CHECK:STDOUT:   uselistorder ptr %30, { 1, 0 }
+// CHECK:STDOUT:   uselistorder i64 %index.next.3, { 1, 0 }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_CSelfDestruct.72395be3dbbe8946:core.Destroy.Core"(ptr %self) local_unnamed_addr #1 !dbg !24 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !26
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nofree norecurse nosync nounwind memory(argmem: readwrite) "tune-cpu"="znver4" }
+// CHECK:STDOUT: attributes #1 = { nounwind "tune-cpu"="znver4" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.dbg.cu = !{!1}
+// CHECK:STDOUT: !llvm.module.flags = !{!62, !63, !64, !70, !71}
+// CHECK:STDOUT: !llvm.errno.tbaa = !{!69}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !DIFile(filename: "foo.carbon", directory: "")
+// CHECK:STDOUT: !1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !0, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !2 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !3 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !4 = !{null, !3}
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !4)
+// CHECK:STDOUT: !6 = !{null, !2}
+// CHECK:STDOUT: !7 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !8 = distinct !DISubprogram(name: "VectorizedWithAvx2", linkageName: "_CVectorizedWithAvx2.Main", scope: null, file: !0, line: 17, type: !5, spFlags: DISPFlagDefinition, unit: !1, retainedNodes: !23)
+// CHECK:STDOUT: !9 = !DILocalVariable(arg: 1, scope: !8, type: !3)
+// CHECK:STDOUT: !13 = !DILocation(line: 21, column: 9, scope: !8)
+// CHECK:STDOUT: !18 = !DILocation(line: 22, column: 5, scope: !8)
+// CHECK:STDOUT: !22 = !DILocation(line: 17, column: 1, scope: !8)
+// CHECK:STDOUT: !23 = !{!9}
+// CHECK:STDOUT: !24 = distinct !DISubprogram(name: "SelfDestruct", linkageName: "_CSelfDestruct.72395be3dbbe8946:core.Destroy.Core", scope: null, file: !0, line: 20, type: !7, spFlags: DISPFlagDefinition, unit: !1, retainedNodes: !27)
+// CHECK:STDOUT: !25 = !DILocalVariable(arg: 1, scope: !24, type: !2)
+// CHECK:STDOUT: !26 = !DILocation(line: 20, column: 3, scope: !24)
+// CHECK:STDOUT: !27 = !{!25}
+// CHECK:STDOUT: !28 = !DIFile(filename: "{{.*}}/prelude/types/int.carbon", directory: "")
+// CHECK:STDOUT: !29 = distinct !DISubprogram(name: "Op", linkageName: "_COp.Int.9452f4c51951679b.Core:Inc.Core.be1e879c1ad406d8", scope: null, file: !28, line: 396, type: !7, spFlags: DISPFlagDefinition, unit: !1, retainedNodes: !36)
+// CHECK:STDOUT: !30 = !DILocalVariable(arg: 1, scope: !29, type: !2)
+// CHECK:STDOUT: !33 = !{null, !2, !2}
+// CHECK:STDOUT: !34 = !DISubroutineType(types: !33)
+// CHECK:STDOUT: !36 = !{!30}
+// CHECK:STDOUT: !37 = distinct !DISubprogram(name: "Op", linkageName: "_COp:thunk:AddAssignWith.b59e374b0649c9ad.Core:Int.9452f4c51951679b.Core:AddAssignWith.ab03190a9e911cb4.Core.306167be98c24f26", scope: null, file: !28, line: 331, type: !34, spFlags: DISPFlagDefinition, unit: !1, retainedNodes: !44)
+// CHECK:STDOUT: !38 = !DILocalVariable(arg: 1, scope: !37, type: !2)
+// CHECK:STDOUT: !39 = !DILocalVariable(arg: 2, scope: !37, type: !2)
+// CHECK:STDOUT: !44 = !{!38, !39}
+// CHECK:STDOUT: !62 = !{i32 8, !"PIC Level", i32 2}
+// CHECK:STDOUT: !63 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !64 = !{i32 7, !"uwtable", i32 2}
+// CHECK:STDOUT: !65 = !{!"Simple C++ TBAA"}
+// CHECK:STDOUT: !66 = !{!"omnipotent char", !65, i64 0}
+// CHECK:STDOUT: !67 = !{!"int", !66, i64 0}
+// CHECK:STDOUT: !68 = !{!"__libc_errno", !67, i64 0}
+// CHECK:STDOUT: !69 = !{!68, !67, i64 0}
+// CHECK:STDOUT: !70 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !71 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !78 = distinct !DILocation(line: 23, column: 5, scope: !8)
+// CHECK:STDOUT: !79 = distinct !DILocation(line: 398, column: 5, scope: !29, inlinedAt: !78)
+// CHECK:STDOUT: !80 = distinct !DILocation(line: 331, column: 3, scope: !37, inlinedAt: !79)
+// CHECK:STDOUT: !85 = !{!"llvm.loop.isvectorized", i32 1}
+// CHECK:STDOUT: !87 = !{!"llvm.loop.unroll.runtime.disable"}
+// CHECK:STDOUT: !88 = distinct !{!88, !85, !87}
+// CHECK:STDOUT: