[ThinLTO] Rename COMDATs for COFF when promoting/renaming COMDAT leader

Summary:
COFF requires that COMDAT name match that of the leader. When we promote
and rename an internal leader in ThinLTO due to an import, ensure we
subsequently rename the associated COMDAT. Similar to D31963 which did
this during ThinLTO module splitting.

Fixes PR40414.

Reviewers: pcc, inglorion

Subscribers: mehdi_amini, dexonsmith, dmajor, llvm-commits

Differential Revision: https://reviews.llvm.org/D57395

llvm-svn: 352763

include/llvm/Transforms/Utils/FunctionImportUtils.h

@@ -43,6 +43,11 @@ class FunctionImportGlobalProcessing {
   /// to promote any non-renamable values.
   SmallPtrSet<GlobalValue *, 8> Used;
 
+  /// Keep track of any COMDATs that require renaming (because COMDAT
+  /// leader was promoted and renamed). Maps from original COMDAT to one
+  /// with new name.
+  DenseMap<const Comdat *, Comdat *> RenamedComdats;
+
   /// Check if we should promote the given local value to global scope.
   bool shouldPromoteLocalToGlobal(const GlobalValue *SGV);
 

lib/Transforms/Utils/FunctionImportUtils.cpp

@@ -248,6 +248,7 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
   bool DoPromote = false;
   if (GV.hasLocalLinkage() &&
       ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
+    auto Name = GV.getName();
     // Once we change the name or linkage it is difficult to determine
     // again whether we should promote since shouldPromoteLocalToGlobal needs
     // to locate the summary (based on GUID from name and linkage). Therefore,
@@ -256,6 +257,12 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
     GV.setLinkage(getLinkage(&GV, DoPromote));
     if (!GV.hasLocalLinkage())
       GV.setVisibility(GlobalValue::HiddenVisibility);
+
+    // If we are renaming a COMDAT leader, ensure that we record the COMDAT
+    // for later renaming as well. This is required for COFF.
+    if (const auto *C = GV.getComdat())
+      if (C->getName() == Name)
+        RenamedComdats.try_emplace(C, M.getOrInsertComdat(GV.getName()));
   } else
     GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));
 
@@ -280,6 +287,16 @@ void FunctionImportGlobalProcessing::processGlobalsForThinLTO() {
     processGlobalForThinLTO(SF);
   for (GlobalAlias &GA : M.aliases())
     processGlobalForThinLTO(GA);
+
+  // Replace any COMDATS that required renaming (because the COMDAT leader was
+  // promoted and renamed).
+  if (!RenamedComdats.empty())
+    for (auto &GO : M.global_objects())
+      if (auto *C = GO.getComdat()) {
+        auto Replacement = RenamedComdats.find(C);
+        if (Replacement != RenamedComdats.end())
+          GO.setComdat(Replacement->second);
+      }
 }
 
 bool FunctionImportGlobalProcessing::run() {

test/Transforms/FunctionImport/Inputs/comdat.ll

@@ -0,0 +1,10 @@
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24215"
+
+define void @main() {
+entry:
+  call i8* @lwt_fun()
+  ret void
+}
+
+declare i8* @lwt_fun()

test/Transforms/FunctionImport/comdat.ll

@@ -0,0 +1,32 @@
+; Test to ensure that comdat is renamed consistently when comdat leader is
+; promoted and renamed due to an import. Required by COFF.
+
+; REQUIRES: x86-registered-target
+
+; RUN: opt -thinlto-bc -o %t1.bc %s
+; RUN: opt -thinlto-bc -o %t2.bc %S/Inputs/comdat.ll
+; RUN: llvm-lto2 run -save-temps -o %t3 %t1.bc %t2.bc \
+; RUN:          -r %t1.bc,lwt_fun,plx \
+; RUN:          -r %t2.bc,main,plx \
+; RUN:          -r %t2.bc,lwt_fun,
+; RUN: llvm-dis -o - %t3.1.3.import.bc | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24215"
+
+; CHECK: $lwt.llvm.[[HASH:[0-9]+]] = comdat any
+$lwt = comdat any
+
+; CHECK: @lwt_aliasee = private unnamed_addr global {{.*}}, comdat($lwt.llvm.[[HASH]])
+@lwt_aliasee = private unnamed_addr global [1 x i8*] [i8* null], comdat($lwt)
+
+; CHECK: @lwt.llvm.[[HASH]] = hidden unnamed_addr alias
+@lwt = internal unnamed_addr alias [1 x i8*], [1 x i8*]* @lwt_aliasee
+
+; Below function should get imported into other module, resulting in @lwt being
+; promoted and renamed.
+define i8* @lwt_fun() {
+  %1 = getelementptr inbounds [1 x i8*], [1 x i8*]* @lwt, i32 0, i32 0
+  %2 = load i8*, i8** %1
+  ret i8* %2
+}