Don't use comdats for initializers on platforms that don't support it

In particular, pre-.init_array ELF uses the .ctors section mechanism.
MinGW COFF also uses .ctors, now that I think about it. Therefore,
restrict this optimization to the two platforms that are currently known
to work: ELF with .init_array and COFF with .CRT$XCU.

llvm-svn: 218287

clang/lib/CodeGen/CGDeclCXX.cpp

@@ -302,7 +302,7 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
                                                           PerformInit);
 
-  llvm::GlobalVariable *Key = supportsCOMDAT() ? Addr : nullptr;
+  llvm::GlobalVariable *Key = supportsCOMDATInitializers() ? Addr : nullptr;
 
   if (D->getTLSKind()) {
     // FIXME: Should we support init_priority for thread_local?

clang/lib/CodeGen/CodeGenModule.h

@@ -601,6 +601,7 @@ public:
   const TargetInfo &getTarget() const { return Target; }
   const llvm::Triple &getTriple() const;
   bool supportsCOMDAT() const;
+  bool supportsCOMDATInitializers() const;
 
   CGCXXABI &getCXXABI() const { return *ABI; }
   llvm::LLVMContext &getLLVMContext() { return VMContext; }

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -1668,7 +1668,8 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
 
     // The ABI says: It is suggested that it be emitted in the same COMDAT group
     // as the associated data object
-    if (!D.isLocalVarDecl() && var->isWeakForLinker() && CGM.supportsCOMDAT()) {
+    if (!D.isLocalVarDecl() && var->isWeakForLinker() &&
+        CGM.supportsCOMDATInitializers()) {
       llvm::Comdat *C = CGM.getModule().getOrInsertComdat(var->getName());
       guard->setComdat(C);
       var->setComdat(C);

clang/lib/CodeGen/TargetInfo.cpp

@@ -6877,6 +6877,14 @@ bool CodeGenModule::supportsCOMDAT() const {
   return !getTriple().isOSBinFormatMachO();
 }
 
+bool CodeGenModule::supportsCOMDATInitializers() const {
+  // We can only put initializers in comdat groups on ELF with .init_array and
+  // COFF with .CRT$XCU.
+  return supportsCOMDAT() &&
+         ((getTriple().isOSBinFormatELF() && getCodeGenOpts().UseInitArray) ||
+          (getTriple().isWindowsMSVCEnvironment()));
+}
+
 const TargetCodeGenInfo &CodeGenModule::getTargetCodeGenInfo() {
   if (TheTargetCodeGenInfo)
     return *TheTargetCodeGenInfo;

clang/test/CodeGenCXX/static-data-member.cpp

@@ -1,4 +1,6 @@
-// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-llvm -fuse-init-array -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-llvm -o - %s | \
+// RUN:     FileCheck %s --check-prefix=CTORS
 // RUN: %clang_cc1 -triple x86_64-apple-darwin -emit-llvm -o - %s | \
 // RUN:     FileCheck --check-prefix=MACHO %s
 
@@ -8,6 +10,8 @@
 // CHECK: @_ZGVN5test31AIiE1xE = weak_odr global i64 0, comdat $_ZN5test31AIiE1xE
 // MACHO: @_ZGVN5test31AIiE1xE = weak_odr global i64 0
 // MACHO-NOT: comdat
+// CTORS: @_ZGVN5test31AIiE1xE = weak_odr global i64 0
+// CTORS-NOT: comdat
 
 // CHECK: _ZN5test51U2k0E = global i32 0
 // CHECK: _ZN5test51U2k1E = global i32 0
@@ -67,6 +71,8 @@ namespace test3 {
   // CHECK-LABEL: define internal void @__cxx_global_var_init1() {{.*}} comdat $_ZN5test31AIiE1xE
   // MACHO-LABEL: define internal void @__cxx_global_var_init1()
   // MACHO-NOT: comdat
+  // CTORS-LABEL: define internal void @__cxx_global_var_init1()
+  // CTORS-NOT: comdat
   // CHECK:      [[GUARDBYTE:%.*]] = load i8* bitcast (i64* @_ZGVN5test31AIiE1xE to i8*)
   // CHECK-NEXT: [[UNINITIALIZED:%.*]] = icmp eq i8 [[GUARDBYTE]], 0
   // CHECK-NEXT: br i1 [[UNINITIALIZED]]

clang/test/CodeGenCXX/static-member-variable-explicit-specialization.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-pc-linux -emit-llvm -o - | FileCheck --check-prefix=ELF --check-prefix=ALL %s
+// RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-pc-linux -fuse-init-array -emit-llvm -o - | FileCheck --check-prefix=ELF --check-prefix=ALL %s
 // RUN: %clang_cc1 %s -std=c++1y -triple=x86_64-apple-darwin -emit-llvm -o - | FileCheck --check-prefix=MACHO --check-prefix=ALL %s
 
 // ALL: ; ModuleID