[llvm][CFI] Do not canonicalize COFF functions in a comdat

COFF requires that a function exists with the same name as a comdat. Not
having this key function results in `LLVM ERROR: Associative COMDAT
symbol '...' does not exist.` CFI by default will attempt to
canonicalize a function by appending `.cfi` to its name which allows
external references to refer to the new canonical alias, but it does not
change the comdat name. We cannot change the comdat name in case the
same comdat is used by other TUs outside this LTO unit. To prevent this,
we can just not canonicalize COFF comdat'd functions.

Author: PiJoules

llvm/lib/Transforms/IPO/LowerTypeTests.cpp

@@ -246,6 +246,18 @@ void ByteArrayBuilder::allocate(const std::set<uint64_t> &Bits,
 bool lowertypetests::isJumpTableCanonical(Function *F) {
   if (F->isDeclarationForLinker())
     return false;
+
+  // Do not canonicalize a comdat'd COFF function because this could end up
+  // renaming the comdat key function without renaming the comdat key. We cannot
+  // rename the key in this LTO unit because other TUs may reference the
+  // original key name. To prevent this, just ignore canonicalization for
+  // comdat'd COFF functions.
+  if (F->hasComdat()) {
+    Triple TargetTriple(F->getParent()->getTargetTriple());
+    if (TargetTriple.isOSBinFormatCOFF())
+      return false;
+  }
+
   auto *CI = mdconst::extract_or_null<ConstantInt>(
       F->getParent()->getModuleFlag("CFI Canonical Jump Tables"));
   if (!CI || !CI->isZero())

llvm/test/Transforms/LowerTypeTests/cfi-canonical-jump-tables-coff.ll

@@ -0,0 +1,30 @@
+; RUN: opt -S -passes=lowertypetests %s -mtriple=x86_64-pc-windows-msvc | llc -asm-verbose=false | FileCheck %s --check-prefixes=COFF,CHECK
+; RUN: opt -S -passes=lowertypetests %s -mtriple=x86_64-unknown-linux-gnu | llc -asm-verbose=false | FileCheck %s --check-prefixes=ELF,CHECK
+
+target datalayout = "e-p:64:64"
+
+; COFF-LABEL: f3:
+; ELF-LABEL:  f3.cfi:
+
+; CHECK-LABEL: a:
+; COFF:          .quad   .L.cfi.jumptable
+; ELF:           .quad   f3
+
+; ELF:  .set f3, .L.cfi.jumptable
+
+@a = global ptr @f3
+
+$f3 = comdat any
+
+define void @f3() comdat !type !0 {
+  ret void
+}
+
+declare i1 @llvm.type.test(ptr %ptr, metadata %bitset) nounwind readnone
+
+define i1 @foo(ptr %p) {
+  %x = call i1 @llvm.type.test(ptr %p, metadata !"typeid1")
+  ret i1 %x
+}
+
+!0 = !{i32 0, !"typeid1"}