[llvm] Change DSOLocalEquivalent type if the underlying global value type changes

We encountered an issue where LTO running on IR that used the DSOLocalEquivalent
constant would result in bad codegen. The underlying issue was ValueMapper wasn't
properly handling DSOLocalEquivalent, so this just adds the machinery for handling
it. This code path is triggered by a fix to DSOLocalEquivalent::handleOperandChangeImpl
where DSOLocalEquivalent could potentially not have the same type as its underlying GV.

This updates DSOLocalEquivalent::handleOperandChangeImpl to change the type if
the GV type changes and handles this constant in ValueMapper.

Differential Revision: https://reviews.llvm.org/D97978

lib/IR/Constants.cpp

@@ -1914,6 +1914,12 @@ Value *DSOLocalEquivalent::handleOperandChangeImpl(Value *From, Value *To) {
   getContext().pImpl->DSOLocalEquivalents.erase(getGlobalValue());
   NewEquiv = this;
   setOperand(0, Func);
+
+  if (Func->getType() != getType()) {
+    // It is ok to mutate the type here because this constant should always
+    // reflect the type of the function it's holding.
+    mutateType(Func->getType());
+  }
   return nullptr;
 }
 

lib/Transforms/Utils/ValueMapper.cpp

@@ -432,6 +432,20 @@ Value *Mapper::mapValue(const Value *V) {
   if (BlockAddress *BA = dyn_cast<BlockAddress>(C))
     return mapBlockAddress(*BA);
 
+  if (const auto *E = dyn_cast<DSOLocalEquivalent>(C)) {
+    auto *Val = mapValue(E->getGlobalValue());
+    GlobalValue *GV = dyn_cast<GlobalValue>(Val);
+    if (GV)
+      return getVM()[E] = DSOLocalEquivalent::get(GV);
+
+    auto *Func = cast<Function>(Val->stripPointerCastsAndAliases());
+    Type *NewTy = E->getType();
+    if (TypeMapper)
+      NewTy = TypeMapper->remapType(NewTy);
+    return getVM()[E] = llvm::ConstantExpr::getBitCast(
+               DSOLocalEquivalent::get(Func), NewTy);
+  }
+
   auto mapValueOrNull = [this](Value *V) {
     auto Mapped = mapValue(V);
     assert((Mapped || (Flags & RF_NullMapMissingGlobalValues)) &&

test/Linker/DSOLocalEquivalent.ll

@@ -0,0 +1,34 @@
+; RUN: llvm-link %s %S/Inputs/DSOLocalEquivalent.ll -S | FileCheck %s
+; RUN: llvm-link %S/Inputs/DSOLocalEquivalent.ll %s -S | FileCheck %s
+
+declare void @extern_func()
+declare void @defined_extern_func()
+declare hidden void @hidden_func()
+
+; CHECK:      define void @call_extern_func() {
+; CHECK-NEXT:   call void dso_local_equivalent @extern_func()
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+define void @call_extern_func() {
+
+  call void dso_local_equivalent @extern_func()
+  ret void
+}
+
+; CHECK:      define void @call_defined_extern_func() {
+; CHECK-NEXT:   call void dso_local_equivalent @defined_extern_func()
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+define void @call_defined_extern_func() {
+  call void dso_local_equivalent @defined_extern_func()
+  ret void
+}
+
+; CHECK:      define void @call_hidden_func() {
+; CHECK-NEXT:   call void dso_local_equivalent @hidden_func()
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+define void @call_hidden_func() {
+  call void dso_local_equivalent @hidden_func()
+  ret void
+}

test/Linker/Inputs/DSOLocalEquivalent.ll

@@ -0,0 +1,7 @@
+define void @defined_extern_func() {
+  ret void
+}
+
+define hidden void @hidden_func() {
+  ret void
+}

test/ThinLTO/X86/DSOLocalEquivalent.ll

@@ -0,0 +1,17 @@
+; RUN: llvm-as %s -o %t1.bc
+; RUN: llvm-lto2 run %t1.bc -o %t2.o -r=%t1.bc,caller,plx -r=%t1.bc,extern_func,plx -save-temps
+; RUN: llvm-dis %t2.o.0.5.precodegen.bc -o - | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-fuchsia"
+
+declare void @extern_func()
+
+; CHECK:      define {{.*}} void @caller() {{.*}}{
+; CHECK-NEXT:   tail call void dso_local_equivalent @extern_func()
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+define void @caller() {
+  call void dso_local_equivalent @extern_func()
+  ret void
+}