From d17609df5f0dfbb90d572473189a21a1483245c5 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Fri, 16 Jan 2026 00:14:53 -0800
Subject: [PATCH] Switch CPU flags to use feature-based selection and apply to
 links (#6611)

Now the CPU flags feature can be unconditionally added as part of the
optimization features and another of the conditions in the main
configuration goes away.

The failure to pass these to links was probably harmless, but it's
better to include it there as well.
---
 .../cc_toolchain_config_features.bzl          | 15 ++++++++++
 .../cc_toolchain_optimization.bzl             | 30 ++++++++++---------
 .../clang_cc_toolchain_config.bzl             | 23 +++++---------
 3 files changed, 38 insertions(+), 30 deletions(-)

diff --git a/bazel/cc_toolchains/cc_toolchain_config_features.bzl b/bazel/cc_toolchains/cc_toolchain_config_features.bzl
index 990190d66a8d..7eeb631d6078 100644
--- a/bazel/cc_toolchains/cc_toolchain_config_features.bzl
+++ b/bazel/cc_toolchains/cc_toolchain_config_features.bzl
@@ -32,3 +32,18 @@ def target_os_features(os):
         fail("Unsupported target OS: %s" % os)
 
     return os_target_features[os]
+
+aarch64_target_feature = feature(name = "aarch64_target", enabled = True)
+x86_64_target_feature = feature(name = "x86_64_target", enabled = True)
+
+cpu_target_features = {
+    "aarch64": [aarch64_target_feature],
+    "arm64": [aarch64_target_feature],
+    "x86_64": [x86_64_target_feature],
+}
+
+def target_cpu_features(cpu):
+    if cpu not in cpu_target_features:
+        fail("Unsupported target CPU: %s" % cpu)
+
+    return cpu_target_features[cpu]
diff --git a/bazel/cc_toolchains/cc_toolchain_optimization.bzl b/bazel/cc_toolchains/cc_toolchain_optimization.bzl
index 1678f3763f19..c0d83d07af9e 100644
--- a/bazel/cc_toolchains/cc_toolchain_optimization.bzl
+++ b/bazel/cc_toolchains/cc_toolchain_optimization.bzl
@@ -10,10 +10,12 @@ load(
     "feature_set",
     "flag_group",
     "flag_set",
+    "with_feature_set",
 )
 load(
     ":cc_toolchain_actions.bzl",
     "all_compile_actions",
+    "all_link_actions",
     "codegen_compile_actions",
 )
 
@@ -43,22 +45,21 @@ default_optimization_flags = feature(
     ],
 )
 
-aarch64_cpu_flags = feature(
+cpu_flags = feature(
     name = "aarch64_cpu_flags",
     enabled = True,
-    flag_sets = [flag_set(
-        actions = all_compile_actions,
-        flag_groups = [flag_group(flags = ["-march=armv8.2-a"])],
-    )],
-)
-
-x86_64_cpu_flags = feature(
-    name = "x86_64_cpu_flags",
-    enabled = True,
-    flag_sets = [flag_set(
-        actions = all_compile_actions,
-        flag_groups = [flag_group(flags = ["-march=x86-64-v2"])],
-    )],
+    flag_sets = [
+        flag_set(
+            actions = all_compile_actions + all_link_actions,
+            flag_groups = [flag_group(flags = ["-march=armv8.2-a"])],
+            with_features = [with_feature_set(["aarch64_target"])],
+        ),
+        flag_set(
+            actions = all_compile_actions + all_link_actions,
+            flag_groups = [flag_group(flags = ["-march=x86-64-v2"])],
+            with_features = [with_feature_set(["x86_64_target"])],
+        ),
+    ],
 )
 
 # Note that the order of features is significant in this list and determines the
@@ -66,4 +67,5 @@ x86_64_cpu_flags = feature(
 optimization_features = [
     minimal_optimization_flags,
     default_optimization_flags,
+    cpu_flags,
 ]
diff --git a/bazel/cc_toolchains/clang_cc_toolchain_config.bzl b/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
index 1a56a7856099..70c82a5faab0 100644
--- a/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
+++ b/bazel/cc_toolchains/clang_cc_toolchain_config.bzl
@@ -26,7 +26,11 @@ load(
     "output_flags_feature",
     "user_flags_feature",
 )
-load(":cc_toolchain_config_features.bzl", "target_os_features")
+load(
+    ":cc_toolchain_config_features.bzl",
+    "target_cpu_features",
+    "target_os_features",
+)
 load(
     ":cc_toolchain_cpp_features.bzl",
     "clang_feature",
@@ -41,12 +45,7 @@ load(
     "macos_link_libraries_feature",
 )
 load(":cc_toolchain_modules.bzl", "modules_features")
-load(
-    ":cc_toolchain_optimization.bzl",
-    "aarch64_cpu_flags",
-    "optimization_features",
-    "x86_64_cpu_flags",
-)
+load(":cc_toolchain_optimization.bzl", "optimization_features")
 load(":cc_toolchain_sanitizer_features.bzl", "sanitizer_features")
 load(
     ":cc_toolchain_tools.bzl",
@@ -128,6 +127,7 @@ def _build_features(ctx):
     features = []
     features += base_features
     features += target_os_features(ctx.attr.target_os)
+    features += target_cpu_features(ctx.attr.target_cpu)
     features += [
         # We always use Clang in the toolchain and enable all of its warnings.
         clang_feature,
@@ -140,16 +140,7 @@ def _build_features(ctx):
         project_flags_feature,
     ]
     features += sanitizer_features
-
     features += optimization_features
-
-    # TODO: Refactor target-specific feature management to be part of
-    # `optimization_features`.
-    if ctx.attr.target_cpu in ["aarch64", "arm64"]:
-        features.append(aarch64_cpu_flags)
-    else:
-        features.append(x86_64_cpu_flags)
-
     features += modules_features
     features += debugging_features
     features += linking_features