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[llvm][CFI] Ensure COFF comdat renaming applies for imported functions #143421

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Jun 16, 2025
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[llvm][CFI] Ensure COFF comdat renaming applies for imported functions #143421

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34 changes: 21 additions & 13 deletions llvm/lib/Transforms/IPO/LowerTypeTests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -561,6 +561,8 @@ class LowerTypeTestsModule {
return FunctionAnnotations.contains(V);
}

void maybeReplaceComdat(Function *F, StringRef OriginalName);

public:
LowerTypeTestsModule(Module &M, ModuleAnalysisManager &AM,
ModuleSummaryIndex *ExportSummary,
Expand Down Expand Up @@ -1082,6 +1084,23 @@ void LowerTypeTestsModule::importTypeTest(CallInst *CI) {
}
}

void LowerTypeTestsModule::maybeReplaceComdat(Function *F,
StringRef OriginalName) {
// For COFF we should also rename the comdat if this function also
// happens to be the key function. Even if the comdat name changes, this
// should still be fine since comdat and symbol resolution happens
// before LTO, so all symbols which would prevail have been selected.
if (F->hasComdat() && ObjectFormat == Triple::COFF &&
F->getComdat()->getName() == OriginalName) {
Comdat *OldComdat = F->getComdat();
Comdat *NewComdat = M.getOrInsertComdat(F->getName());
for (GlobalObject &GO : M.global_objects()) {
if (GO.getComdat() == OldComdat)
GO.setComdat(NewComdat);
}
}
}

// ThinLTO backend: the function F has a jump table entry; update this module
// accordingly. isJumpTableCanonical describes the type of the jump table entry.
void LowerTypeTestsModule::importFunction(
Expand Down Expand Up @@ -1115,6 +1134,7 @@ void LowerTypeTestsModule::importFunction(
FDecl->setVisibility(GlobalValue::HiddenVisibility);
} else {
F->setName(Name + ".cfi");
maybeReplaceComdat(F, Name);
F->setLinkage(GlobalValue::ExternalLinkage);
FDecl = Function::Create(F->getFunctionType(), GlobalValue::ExternalLinkage,
F->getAddressSpace(), Name, &M);
Expand Down Expand Up @@ -1734,19 +1754,7 @@ void LowerTypeTestsModule::buildBitSetsFromFunctionsNative(
FAlias->takeName(F);
if (FAlias->hasName()) {
F->setName(FAlias->getName() + ".cfi");
// For COFF we should also rename the comdat if this function also
// happens to be the key function. Even if the comdat name changes, this
// should still be fine since comdat and symbol resolution happens
// before LTO, so all symbols which would prevail have been selected.
if (F->hasComdat() && ObjectFormat == Triple::COFF &&
F->getComdat()->getName() == FAlias->getName()) {
Comdat *OldComdat = F->getComdat();
Comdat *NewComdat = M.getOrInsertComdat(F->getName());
for (GlobalObject &GO : M.global_objects()) {
if (GO.getComdat() == OldComdat)
GO.setComdat(NewComdat);
}
}
maybeReplaceComdat(F, FAlias->getName());
}
replaceCfiUses(F, FAlias, IsJumpTableCanonical);
if (!F->hasLocalLinkage())
Expand Down
5 changes: 5 additions & 0 deletions llvm/test/Transforms/LowerTypeTests/Inputs/import-thinlto-funcs.yaml
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@@ -0,0 +1,5 @@
---
CfiFunctionDefs:
- f1
- f2
...
2 changes: 2 additions & 0 deletions llvm/test/Transforms/LowerTypeTests/cfi-coff-comdat-rename.ll
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@@ -1,12 +1,14 @@
; REQUIRES: x86-registered-target
; RUN: opt -S -passes=lowertypetests %s | FileCheck %s
; RUN: opt -S -passes=lowertypetests -lowertypetests-summary-action=import -lowertypetests-read-summary=%p/Inputs/import-thinlto-funcs.yaml %s | FileCheck %s

;; This is a check to assert we don't crash with:
;;
;; LLVM ERROR: Associative COMDAT symbol '...' does not exist.
;;
;; So this just needs to exit normally.
; RUN: opt -S -passes=lowertypetests %s | llc -asm-verbose=false
; RUN: opt -S -passes=lowertypetests -lowertypetests-summary-action=import -lowertypetests-read-summary=%p/Inputs/import-thinlto-funcs.yaml %s | llc -asm-verbose=false

target datalayout = "e-p:64:64"
target triple = "x86_64-pc-windows-msvc"
Expand Down
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