[HotColdSplit] Don't outline musttail calls. #133177
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musttail calls have several restrictions, generally enforcing matching calling conventions between the caller parent and musttail callee. We can't usually honor them, because the extracted function has a different signature altogether, taking inputs/outputs and returning a control-flow identifier rather than the actual return value. Don't consider musttail calls as valid for extraction.
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@llvm/pr-subscribers-llvm-transforms Author: Ahmed Bougacha (ahmedbougacha) Changesmusttail calls have several restrictions, generally enforcing matching calling conventions between the caller parent and musttail callee. We can't usually honor them, because the extracted function has a different signature altogether, taking inputs/outputs and returning a control-flow identifier rather than the actual return value. Don't consider musttail calls as valid for extraction. Full diff: https://github.com/llvm/llvm-project/pull/133177.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index 7277603b3ec2b..216db3a4570f7 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -170,6 +170,14 @@ static bool isBlockValidForExtraction(const BasicBlock &BB,
}
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
+ // musttail calls have several restrictions, generally enforcing matching
+ // calling conventions between the caller parent and musttail callee.
+ // We can't usually honor them, because the extracted function has a
+ // different signature altogether, taking inputs/outputs and returning
+ // a control-flow identifier rather than the actual return value.
+ if (CI->isMustTailCall())
+ return false;
+
if (const Function *F = CI->getCalledFunction()) {
auto IID = F->getIntrinsicID();
if (IID == Intrinsic::vastart) {
diff --git a/llvm/test/Transforms/HotColdSplit/musttail.ll b/llvm/test/Transforms/HotColdSplit/musttail.ll
new file mode 100644
index 0000000000000..b7108bd6e6cd9
--- /dev/null
+++ b/llvm/test/Transforms/HotColdSplit/musttail.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=hotcoldsplit -hotcoldsplit-threshold=0 -S < %s | FileCheck %s
+
+; musttail calls can't be outlined, because they have several restrictions
+; enforcing matching calling conventions between the parent and callee.
+
+define void @test_musttail(i1 %b) {
+; CHECK-LABEL: define void @test_musttail(
+; CHECK-SAME: i1 [[B:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[B]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
+; CHECK: [[IF_THEN]]:
+; CHECK-NEXT: ret void
+; CHECK: [[IF_ELSE]]:
+; CHECK-NEXT: musttail call void @target(i1 [[B]])
+; CHECK-NEXT: ret void
+;
+entry:
+ br i1 %b, label %if.then, label %if.else
+
+if.then:
+ ret void
+
+if.else:
+ musttail call void @target(i1 %b)
+ ret void
+}
+
+define void @test_tail(i1 %b) {
+; CHECK-LABEL: define void @test_tail(
+; CHECK-SAME: i1 [[B:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: br i1 [[B]], label %[[IF_THEN:.*]], label %[[CODEREPL:.*]]
+; CHECK: [[IF_THEN]]:
+; CHECK-NEXT: ret void
+; CHECK: [[CODEREPL]]:
+; CHECK-NEXT: call void @test_tail.cold.1(i1 [[B]]) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT: br label %[[IF_ELSE_RET:.*]]
+; CHECK: [[IF_ELSE_RET]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br i1 %b, label %if.then, label %if.else
+
+if.then:
+ ret void
+
+if.else:
+ tail call void @target(i1 %b)
+ ret void
+}
+
+declare void @target() cold
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jroelofs
approved these changes
Mar 26, 2025
hstk30-hw
approved these changes
Mar 27, 2025
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/18/builds/13685 Here is the relevant piece of the build log for the reference |
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musttail calls have several restrictions, generally enforcing matching calling conventions between the caller parent and musttail callee. We can't usually honor them, because the extracted function has a different signature altogether, taking inputs/outputs and returning a control-flow identifier rather than the actual return value.
Don't consider musttail calls as valid for extraction.