Switch CARBON_CHECK to a format string API (#4285)

This switches `DCHECK` and `FATAL` as well.

The goal is to reduce the code size impact of these assertions so that
we can keep more of them enabled. Currently, the largest cost I see from
`CHECK` is not the actual check or the cold code itself, but actually
the failure to inline trivial functions due to the presence of the cold
code. This means that our goal isn't to reduce apparent code size in the
final binary but the LLVM IR cost assessed for these routines in the
inliner, which closely correlates with code size but is a bit different.

As discussed in #4283, experimentation shows that a single function call
with a minimal number of arguments is the lowest cost model for these.
This is easily achieved with a format-string API that internally uses
`llvm::formatv`. This PR is essentially the `CHECK` version of #4283.

However, the check macros are substantially harder to make work with
both format strings and streaming because they also take a condition.
Also, unexpectedly, I was very successful at devising a regular
expression based automated rewrite from the streaming to the format
string form with only low 10s of manual fixes. This includes compacting
strings broken up across lines, etc. Given how well that went, I've
prepared this PR which just directly switches to the format string API
and migrate everything to use it.

One nice side-effect is that the format string approach ends up greatly
simplifying the implementation here as well.

This is ... *shockingly* effective. Parsing speeds up by more than 3%
with just this change. And checking speeds up by **8%** with this change
alone:
```
BM_CompileAPIFileDenseDecls<Phase::Parse>/256      86.3µs ± 1%  82.9µs ± 1%  -3.94%  (p=0.000 n=17+19)
BM_CompileAPIFileDenseDecls<Phase::Parse>/1024      431µs ± 1%   415µs ± 1%  -3.76%  (p=0.000 n=18+19)
BM_CompileAPIFileDenseDecls<Phase::Parse>/4096     1.77ms ± 1%  1.71ms ± 1%  -3.18%  (p=0.000 n=18+19)
BM_CompileAPIFileDenseDecls<Phase::Parse>/16384    7.44ms ± 1%  7.17ms ± 2%  -3.56%  (p=0.000 n=18+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/65536    30.7ms ± 1%  29.7ms ± 1%  -3.15%  (p=0.000 n=18+20)
BM_CompileAPIFileDenseDecls<Phase::Parse>/262144    131ms ± 1%   127ms ± 1%  -2.81%  (p=0.000 n=18+18)
BM_CompileAPIFileDenseDecls<Phase::Check>/256       878µs ± 2%   800µs ± 1%  -8.91%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Check>/1024     1.88ms ± 2%  1.72ms ± 1%  -8.56%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Check>/4096     5.78ms ± 2%  5.28ms ± 1%  -8.70%  (p=0.000 n=20+18)
BM_CompileAPIFileDenseDecls<Phase::Check>/16384    21.9ms ± 1%  20.1ms ± 1%  -8.02%  (p=0.000 n=18+20)
BM_CompileAPIFileDenseDecls<Phase::Check>/65536    90.4ms ± 2%  83.1ms ± 1%  -8.04%  (p=0.000 n=19+20)
BM_CompileAPIFileDenseDecls<Phase::Check>/262144    381ms ± 2%   352ms ± 1%  -7.79%  (p=0.000 n=19+19)
```

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>

toolchain/lower/function_context.cpp

@@ -66,15 +66,14 @@ template <typename InstT>
 static auto LowerInstHelper(FunctionContext& context, SemIR::InstId inst_id,
                             InstT inst) {
   if constexpr (!InstT::Kind.is_lowered()) {
-    CARBON_FATAL()
-        << "Encountered an instruction that isn't expected to lower. It's "
-           "possible that logic needs to be changed in order to stop "
-           "showing this instruction in lowered contexts. Instruction: "
-        << inst;
+    CARBON_FATAL(
+        "Encountered an instruction that isn't expected to lower. It's "
+        "possible that logic needs to be changed in order to stop showing this "
+        "instruction in lowered contexts. Instruction: {0}",
+        inst);
   } else if constexpr (InstT::Kind.constant_kind() ==
                        SemIR::InstConstantKind::Always) {
-    CARBON_FATAL() << "Missing constant value for constant instruction "
-                   << inst;
+    CARBON_FATAL("Missing constant value for constant instruction {0}", inst);
   } else if constexpr (InstT::Kind.is_type() == SemIR::InstIsType::Always) {
     // For instructions that are always of type `type`, produce the trivial
     // runtime representation of type `type`.
@@ -99,9 +98,9 @@ auto FunctionContext::LowerInst(SemIR::InstId inst_id) -> void {
   builder_.getInserter().SetCurrentInstId(inst_id);
   if (di_subprogram_) {
     auto loc = file_context_->GetLocForDI(inst_id);
-    CARBON_CHECK(loc.filename == di_subprogram_->getFile()->getFilename())
-        << "Instructions located in a different file from their enclosing "
-           "function aren't handled yet";
+    CARBON_CHECK(loc.filename == di_subprogram_->getFile()->getFilename(),
+                 "Instructions located in a different file from their "
+                 "enclosing function aren't handled yet");
     builder_.SetCurrentDebugLocation(
         llvm::DILocation::get(builder_.getContext(), loc.line_number,
                               loc.column_number, di_subprogram_));
@@ -129,9 +128,9 @@ auto FunctionContext::GetBlockArg(SemIR::InstBlockId block_id,
   // Find the existing phi, if any.
   auto phis = block->phis();
   if (!phis.empty()) {
-    CARBON_CHECK(std::next(phis.begin()) == phis.end())
-        << "Expected at most one phi, found "
-        << std::distance(phis.begin(), phis.end());
+    CARBON_CHECK(std::next(phis.begin()) == phis.end(),
+                 "Expected at most one phi, found {0}",
+                 std::distance(phis.begin(), phis.end()));
     return &*phis.begin();
   }
 
@@ -163,8 +162,8 @@ auto FunctionContext::FinishInit(SemIR::TypeId type_id, SemIR::InstId dest_id,
       CopyValue(type_id, source_id, dest_id);
       break;
     case SemIR::InitRepr::Incomplete:
-      CARBON_FATAL() << "Lowering aggregate initialization of incomplete type "
-                     << sem_ir().types().GetAsInst(type_id);
+      CARBON_FATAL("Lowering aggregate initialization of incomplete type {0}",
+                   sem_ir().types().GetAsInst(type_id));
   }
 }
 
@@ -172,7 +171,7 @@ auto FunctionContext::CopyValue(SemIR::TypeId type_id, SemIR::InstId source_id,
                                 SemIR::InstId dest_id) -> void {
   switch (auto rep = SemIR::ValueRepr::ForType(sem_ir(), type_id); rep.kind) {
     case SemIR::ValueRepr::Unknown:
-      CARBON_FATAL() << "Attempt to copy incomplete type";
+      CARBON_FATAL("Attempt to copy incomplete type");
     case SemIR::ValueRepr::None:
       break;
     case SemIR::ValueRepr::Copy:
@@ -182,7 +181,7 @@ auto FunctionContext::CopyValue(SemIR::TypeId type_id, SemIR::InstId source_id,
       CopyObject(type_id, source_id, dest_id);
       break;
     case SemIR::ValueRepr::Custom:
-      CARBON_FATAL() << "TODO: Add support for CopyValue with custom value rep";
+      CARBON_FATAL("TODO: Add support for CopyValue with custom value rep");
   }
 }