r224369 - Put static local variables of inline functions in the function comdat.

[Rafael Espindola]

Author: rafael
Date: Tue Dec 16 15:00:30 2014
New Revision: 224369

URL: http://llvm.org/viewvc/llvm-project?rev=224369&view=rev
Log:
Put static local variables of inline functions in the function comdat.

The variable (and the GV) is only ever used if the function is. Putting it
in the function's comdat make it easier for the linker to discard them.

The motivating example is

struct S {
  static const int x;
};
// const int S::x = 42;
inline const int *f() {
  static const int y = S::x;
  return &y;
}
const int *g() { return f(); }

With S::x commented out, _ZZ1fvE1y is a variable with a guard variable
that is initialized by f.

With S::x present, _ZZ1fvE1y is a constant.

Modified:
    cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp
    cfe/trunk/test/CodeGenCXX/static-init.cpp

Modified: cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp?rev=224369&r1=224368&r2=224369&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp (original)
+++ cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp Tue Dec 16 15:00:30 2014
@@ -1711,8 +1711,10 @@ void ItaniumCXXABI::EmitGuardedInit(Code
 
     // 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()) {
-      llvm::Comdat *C = CGM.getModule().getOrInsertComdat(var->getName());
+    if (var->isWeakForLinker() && CGM.supportsCOMDAT()) {
+      StringRef ComdatName =
+        D.isLocalVarDecl() ? CGF.CurFn->getName() : var->getName();
+      llvm::Comdat *C = CGM.getModule().getOrInsertComdat(ComdatName);
       guard->setComdat(C);
       var->setComdat(C);
       CGF.CurFn->setComdat(C);

Modified: cfe/trunk/test/CodeGenCXX/static-init.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/static-init.cpp?rev=224369&r1=224368&r2=224369&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/static-init.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/static-init.cpp Tue Dec 16 15:00:30 2014
@@ -7,10 +7,8 @@
 // CHECK: @_ZZN5test31BC1EvE1u = internal global { i8, [3 x i8] } { i8 97, [3 x i8] undef }, align 4
 // CHECK: @_ZZN5test1L6getvarEiE3var = internal constant [4 x i32] [i32 1, i32 0, i32 2, i32 4], align 16
 
-// CHECK: @_ZZ2h2vE1i = linkonce_odr global i32 0
-// CHECK-NOT: comdat
-// CHECK: @_ZGVZ2h2vE1i = linkonce_odr global i64 0
-// CHECK-NOT: comdat
+// CHECK: @_ZZ2h2vE1i = linkonce_odr global i32 0, comdat $_Z2h2v
+// CHECK: @_ZGVZ2h2vE1i = linkonce_odr global i64 0, comdat $_Z2h2v
 
 struct A {
   A();
@@ -37,8 +35,7 @@ void h() {
   static const int i = a();
 }
 
-// CHECK: define linkonce_odr void @_Z2h2v()
-// CHECK-NOT: comdat
+// CHECK: define linkonce_odr void @_Z2h2v() {{.*}} comdat $_Z2h2v
 inline void h2() {
   static int i = a();
 }