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Make x86 __ehhandler comdat if parent function is

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Summary:
This change comes from using lld for i686-windows-msvc. Before this change, lld
emits an error of:

    error: relocation against symbol in discarded section: .xdata

It's possible that this could be addressed in lld, but I think this change is
reasonable on its own.

At a high level, this is being generated:

    A (.text comdat) -> B (.text) -> C (.xdata comdat)

Where A is a C++ inline function, which references B, an exception handler
thunk, which references C, the exception handling info.

With this structure, lld will error when applying relocations to B if the C it
references has been discarded (some other C has been selected).

This change checks if A is comdat, and if so places the exception registration
thunk (B) in the comdata group of A (and B).

It appears that MSVC makes the __ehhandler function comdat.

Is it possible that duplicate thunks are being emitted into the final binary
with other linkers, or are they stripping the unused thunks?

Reviewers: rnk, majnemer, compnerd, smeenai

Reviewed By: rnk, compnerd

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38940

llvm-svn: 316219
This commit is contained in:
Dave Lee 2017-10-20 17:04:43 +00:00
parent a1de44f546
commit 8f61c481f3
2 changed files with 19 additions and 0 deletions
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2
lib/Target/X86/X86WinEHState.cpp
View File

@ -401,6 +401,8 @@ Function *WinEHStatePass::generateLSDAInEAXThunk(Function *ParentFunc) {
Twine("__ehhandler$") + GlobalValue::dropLLVMManglingEscape(
ParentFunc->getName()),
TheModule);
if (auto *C = ParentFunc->getComdat())
Trampoline->setComdat(C);
BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", Trampoline);
IRBuilder<> Builder(EntryBB);
Value *LSDA = emitEHLSDA(Builder, ParentFunc);

17
test/CodeGen/WinEH/wineh-comdat.ll Normal file
View File

@ -0,0 +1,17 @@
; RUN: opt -mtriple=i686-unknown-windows-msvc -S -x86-winehstate < %s | FileCheck %s
$f = comdat any
define void @f() comdat personality i32 (...)* @__CxxFrameHandler3 {
invoke void @g() to label %return unwind label %unwind
return:
ret void
unwind:
%pad = cleanuppad within none []
cleanupret from %pad unwind to caller
}
declare void @g()
declare i32 @__CxxFrameHandler3(...)
; CHECK: define internal i32 @"__ehhandler$f"(i8*, i8*, i8*, i8*){{ .+}} comdat($f) {