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

llvm-svn: 316219

1 files changed, 17 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/WinEH/wineh-comdat.ll b/llvm/test/CodeGen/WinEH/wineh-comdat.ll
new file mode 100644
index 00000000000..5484370a767
--- /dev/null
+++ b/llvm/test/CodeGen/WinEH/wineh-comdat.ll
@@ -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) {