Re: Put more stuff in the comdat used for variables with static init

[Rafael Espíndola]

On 16 September 2014 12:28, David Majnemer <david.majne...@gmail.com> wrote:
> I think we should have clang omit comdats, it would be confusing to silently
> ignore comdats in llvm.
>

Yes, that is probably best.

What about the attached patch?

Cheers,
Rafael

diff --git a/lib/CodeGen/CGDeclCXX.cpp b/lib/CodeGen/CGDeclCXX.cpp
index 3e5f42e..3f1e4e8 100644
--- a/lib/CodeGen/CGDeclCXX.cpp
+++ b/lib/CodeGen/CGDeclCXX.cpp
@@ -298,6 +298,11 @@ CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
   llvm::Function *Fn =
       CreateGlobalInitOrDestructFunction(*this, FTy, FnName.str());
 
+  if (Addr->isWeakForLinker() && supportsCOMDAT()) {
+    llvm::Comdat *C = TheModule.getOrInsertComdat(Addr->getName());
+    Fn->setComdat(C);
+  }
+
   auto *ISA = D->getAttr<InitSegAttr>();
   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
                                                           PerformInit);
diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index b36d4a6..a095c9d 100644
--- a/lib/CodeGen/CodeGenModule.h
+++ b/lib/CodeGen/CodeGenModule.h
@@ -599,6 +599,9 @@ public:
   DiagnosticsEngine &getDiags() const { return Diags; }
   const llvm::DataLayout &getDataLayout() const { return TheDataLayout; }
   const TargetInfo &getTarget() const { return Target; }
+  const llvm::Triple &getTriple() const;
+  bool supportsCOMDAT() const;
+
   CGCXXABI &getCXXABI() const { return *ABI; }
   llvm::LLVMContext &getLLVMContext() { return VMContext; }
 
diff --git a/lib/CodeGen/ItaniumCXXABI.cpp b/lib/CodeGen/ItaniumCXXABI.cpp
index 4a24e77..865831f 100644
--- a/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1666,6 +1666,13 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
     // If the variable is thread-local, so is its guard variable.
     guard->setThreadLocalMode(var->getThreadLocalMode());
 
+    // The ABI says: It is suggested that it be emitted in the same COMDAT group
+    // as the associated data object
+    if (var->isWeakForLinker() && CGM.supportsCOMDAT()) {
+      llvm::Comdat *C = CGM.getModule().getOrInsertComdat(var->getName());
+      guard->setComdat(C);
+    }
+
     CGM.setStaticLocalDeclGuardAddress(&D, guard);
   }
 
diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index 9bf1dbb..cca825c 100644
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -6868,6 +6868,14 @@ static bool getTypeString(SmallStringEnc &Enc, const Decl *D,
 // Driver code
 //===----------------------------------------------------------------------===//
 
+const llvm::Triple &CodeGenModule::getTriple() const {
+  return getTarget().getTriple();
+}
+
+bool CodeGenModule::supportsCOMDAT() const {
+  return !getTriple().isOSBinFormatMachO();
+}
+
 const TargetCodeGenInfo &CodeGenModule::getTargetCodeGenInfo() {
   if (TheTargetCodeGenInfo)
     return *TheTargetCodeGenInfo;
diff --git a/test/CodeGenCXX/static-data-member.cpp b/test/CodeGenCXX/static-data-member.cpp
index eea9794..c4ac859 100644
--- a/test/CodeGenCXX/static-data-member.cpp
+++ b/test/CodeGenCXX/static-data-member.cpp
@@ -1,9 +1,13 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -emit-llvm -o - %s | \
+// RUN: FileCheck --check-prefix=MACHO %s
 
 // CHECK: @_ZN5test11A1aE = constant i32 10, align 4
 // CHECK: @_ZN5test212_GLOBAL__N_11AIiE1xE = internal global i32 0, align 4
 // CHECK: @_ZN5test31AIiE1xE = weak_odr global i32 0, align 4
-// CHECK: @_ZGVN5test31AIiE1xE = weak_odr global i64 0
+// CHECK: @_ZGVN5test31AIiE1xE = weak_odr global i64 0, comdat $_ZN5test31AIiE1xE
+// MACHO: @_ZGVN5test31AIiE1xE = weak_odr global i64 0
+// MACHO-NOT: comdat
 
 // CHECK: _ZN5test51U2k0E = global i32 0
 // CHECK: _ZN5test51U2k1E = global i32 0
@@ -60,7 +64,9 @@ namespace test3 {
   template <class T> int A<T>::x = foo();
   template struct A<int>;
 
-  // CHECK-LABEL: define internal void @__cxx_global_var_init1()
+  // CHECK-LABEL: define internal void @__cxx_global_var_init1() {{.*}} comdat $_ZN5test31AIiE1xE
+  // MACHO-LABEL: define internal void @__cxx_global_var_init1()
+  // MACHO-NOT: comdat
   // CHECK:      [[GUARDBYTE:%.*]] = load i8* bitcast (i64* @_ZGVN5test31AIiE1xE to i8*)
   // CHECK-NEXT: [[UNINITIALIZED:%.*]] = icmp eq i8 [[GUARDBYTE]], 0
   // CHECK-NEXT: br i1 [[UNINITIALIZED]]

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