[llvm] [ctxprof] Don't lower instrumentation for `noreturn` functions (PR #134932)

[Mircea Trofin via llvm-commits]

https://github.com/mtrofin created https://github.com/llvm/llvm-project/pull/134932

None

>From b7a0761e6ce77844964c40ad16931d019d6292ab Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtrofin at google.com>
Date: Tue, 8 Apr 2025 14:20:39 -0700
Subject: [PATCH] [ctxprof] Don't lower instrumentation for `noreturn`
 functions

---
 .../Instrumentation/PGOCtxProfLowering.cpp    | 12 ++++++++++
 .../PGOProfile/ctx-instrumentation.ll         | 22 ++++++++++++++++---
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
index 2f8d7766bb588..a314457423819 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOCtxProfLowering.cpp
@@ -8,6 +8,7 @@
 //
 
 #include "llvm/Transforms/Instrumentation/PGOCtxProfLowering.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Analysis/CtxProfAnalysis.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/IR/Analysis.h"
@@ -206,6 +207,17 @@ PreservedAnalyses PGOCtxProfLoweringPass::run(Module &M,
 bool CtxInstrumentationLowerer::lowerFunction(Function &F) {
   if (F.isDeclaration())
     return false;
+
+  // Probably pointless to try to do anything here, unlikely to be
+  // performance-affecting.
+  if (F.doesNotReturn()) {
+    for (auto &BB : F)
+      for (auto &I : make_early_inc_range(BB))
+        if (isa<InstrProfCntrInstBase>(&I))
+          I.eraseFromParent();
+    return true;
+  }
+
   auto &FAM = MAM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
   auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 
diff --git a/llvm/test/Transforms/PGOProfile/ctx-instrumentation.ll b/llvm/test/Transforms/PGOProfile/ctx-instrumentation.ll
index 75f292deb71c2..8f72711a9c8b1 100644
--- a/llvm/test/Transforms/PGOProfile/ctx-instrumentation.ll
+++ b/llvm/test/Transforms/PGOProfile/ctx-instrumentation.ll
@@ -310,11 +310,26 @@ define void @has_musttail_calls() {
   musttail call void @bar()
   ret void
 }
+
+define void @does_not_return() noreturn {
+; INSTRUMENT-LABEL: define void @does_not_return(
+; INSTRUMENT-SAME: ) #[[ATTR0:[0-9]+]] {
+; INSTRUMENT-NEXT:    call void @llvm.instrprof.increment(ptr @does_not_return, i64 742261418966908927, i32 1, i32 0)
+; INSTRUMENT-NEXT:    unreachable
+;
+; LOWERING-LABEL: define void @does_not_return(
+; LOWERING-SAME: ) #[[ATTR0:[0-9]+]] !guid [[META8:![0-9]+]] {
+; LOWERING-NEXT:    unreachable
+;
+  unreachable
+}
 ;.
-; LOWERING: attributes #[[ATTR0:[0-9]+]] = { nounwind }
-; LOWERING: attributes #[[ATTR1:[0-9]+]] = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
+; LOWERING: attributes #[[ATTR0]] = { noreturn }
+; LOWERING: attributes #[[ATTR1:[0-9]+]] = { nounwind }
+; LOWERING: attributes #[[ATTR2:[0-9]+]] = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
 ;.
-; INSTRUMENT: attributes #[[ATTR0:[0-9]+]] = { nounwind }
+; INSTRUMENT: attributes #[[ATTR0]] = { noreturn }
+; INSTRUMENT: attributes #[[ATTR1:[0-9]+]] = { nounwind }
 ;.
 ; LOWERING: [[META0]] = !{i64 6699318081062747564}
 ; LOWERING: [[META1]] = !{i64 4909520559318251808}
@@ -324,4 +339,5 @@ define void @has_musttail_calls() {
 ; LOWERING: [[META5]] = !{i64 5458232184388660970}
 ; LOWERING: [[META6]] = !{i64 -3771893999295659109}
 ; LOWERING: [[META7]] = !{i64 -4680624981836544329}
+; LOWERING: [[META8]] = !{i64 5519225910966780583}
 ;.