[llvm] r316219 - Make x86 __ehhandler comdat if parent function is

[Dave Lee via llvm-commits]

Author: kastiglione
Date: Fri Oct 20 10:04:43 2017
New Revision: 316219

URL: http://llvm.org/viewvc/llvm-project?rev=316219&view=rev
Log:
Make x86 __ehhandler comdat if parent function is

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

Added:
    llvm/trunk/test/CodeGen/WinEH/wineh-comdat.ll
Modified:
    llvm/trunk/lib/Target/X86/X86WinEHState.cpp

Modified: llvm/trunk/lib/Target/X86/X86WinEHState.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86WinEHState.cpp?rev=316219&r1=316218&r2=316219&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86WinEHState.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86WinEHState.cpp Fri Oct 20 10:04:43 2017
@@ -401,6 +401,8 @@ Function *WinEHStatePass::generateLSDAIn
                        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);

Added: llvm/trunk/test/CodeGen/WinEH/wineh-comdat.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WinEH/wineh-comdat.ll?rev=316219&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/WinEH/wineh-comdat.ll (added)
+++ llvm/trunk/test/CodeGen/WinEH/wineh-comdat.ll Fri Oct 20 10:04:43 2017
@@ -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) {