Produce direct calls instead of alias to linkonce_odr functions.

This is a small optimization on linux, but should help more on windows
where msvc only outputs one destructor if there would be two identical ones.

llvm-svn: 194046

3 files changed, 29 insertions, 25 deletions

diff --git a/clang/lib/CodeGen/CGCXX.cpp b/clang/lib/CodeGen/CGCXX.cpp
index 25f3e6f4daa..ab45e321cbb 100644
--- a/clang/lib/CodeGen/CGCXX.cpp
+++ b/clang/lib/CodeGen/CGCXX.cpp
@@ -112,28 +112,13 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
   // support aliases with that linkage, fail.
   llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
 
-  llvm::GlobalValue::LinkageTypes TargetLinkage
-    = getFunctionLinkage(TargetDecl);
-
-  // Don't create an alias to a linker weak symbol unless we know we can do
-  // that in every TU. This avoids producing different COMDATs in different
-  // TUs.
-  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) {
-    if (!InEveryTU)
-      return true;
-
-    // In addition to making sure we produce it in every TU, we have to make
-    // sure llvm keeps it.
-    // FIXME: Instead of outputting an alias we could just replace every use of
-    // AliasDecl with TargetDecl.
-    assert(Linkage == TargetLinkage);
-    Linkage = llvm::GlobalValue::WeakODRLinkage;
-  }
-
   // We can't use an alias if the linkage is not valid for one.
   if (!llvm::GlobalAlias::isValidLinkage(Linkage))
     return true;
 
+  llvm::GlobalValue::LinkageTypes TargetLinkage =
+      getFunctionLinkage(TargetDecl);
+
   // Check if we have it already.
   StringRef MangledName = getMangledName(AliasDecl);
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
@@ -152,6 +137,26 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
   if (Ref->getType() != AliasType)
     Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
 
+  // Don't create an alias to a linker weak symbol unless we know we can do
+  // that in every TU. This avoids producing different COMDATs in different
+  // TUs.
+  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) {
+    if (!InEveryTU)
+      return true;
+
+    assert(Linkage == TargetLinkage);
+    // Instead of creating as alias to a linkonce_odr, replace all of the uses
+    // of the aliassee.
+    if (TargetLinkage == llvm::GlobalValue::LinkOnceODRLinkage) {
+      if (!Entry)
+        return false;
+
+      Entry->replaceAllUsesWith(Aliasee);
+      Entry->eraseFromParent();
+      return false;
+    }
+  }
+
   // Create the alias with no name.
   llvm::GlobalAlias *Alias = 
     new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());
diff --git a/clang/test/CodeGenCXX/ctor-dtor-alias.cpp b/clang/test/CodeGenCXX/ctor-dtor-alias.cpp
index e658522d799..ff9bd7c5c5c 100644
--- a/clang/test/CodeGenCXX/ctor-dtor-alias.cpp
+++ b/clang/test/CodeGenCXX/ctor-dtor-alias.cpp
@@ -13,12 +13,11 @@ template struct foobar<void>;
 }
 
 namespace test2 {
-// test that we produce an alias when the destrucor is linkonce_odr. Note that
-// the alias itself is weak_odr to make sure we don't get a translation unit
-// with just _ZN5test26foobarIvEC2Ev in it.
+// test that when the destrucor is linkonce_odr we just replace every use of
+// C1 with C2.
 
-// CHECK-DAG: @_ZN5test26foobarIvEC1Ev = alias weak_odr void (%"struct.test2::foobar"*)* @_ZN5test26foobarIvEC2Ev
 // CHECK-DAG: define linkonce_odr void @_ZN5test26foobarIvEC2Ev(
+// CHECK-DAG: call void @_ZN5test26foobarIvEC2Ev
 void g();
 template <typename T> struct foobar {
   foobar() { g(); }
@@ -48,9 +47,7 @@ namespace test4 {
   // Test that we don't produce aliases from B to A. We cannot because we cannot
   // guarantee that they will be present in every TU.
 
-  // CHECK-DAG: @_ZN5test41BD1Ev = alias weak_odr void (%"struct.test4::B"*)* @_ZN5test41BD2Ev
   // CHECK-DAG: define linkonce_odr void @_ZN5test41BD2Ev(
-  // CHECK-DAG: @_ZN5test41AD1Ev = alias weak_odr void (%"struct.test4::A"*)* @_ZN5test41AD2Ev
   // CHECK-DAG: define linkonce_odr void @_ZN5test41AD2Ev(
   struct A {
     virtual ~A() {}
diff --git a/clang/test/CodeGenCXX/destructors.cpp b/clang/test/CodeGenCXX/destructors.cpp
index 0030aae92ed..fa7df1babf8 100644
--- a/clang/test/CodeGenCXX/destructors.cpp
+++ b/clang/test/CodeGenCXX/destructors.cpp
@@ -9,7 +9,6 @@
 // CHECK-DAG: @_ZN5test312_GLOBAL__N_11DD1Ev = alias internal {{.*}} @_ZN5test312_GLOBAL__N_11DD2Ev
 // CHECK-DAG: @_ZN5test312_GLOBAL__N_11DD2Ev = alias internal bitcast {{.*}} @_ZN5test312_GLOBAL__N_11CD2Ev
 // CHECK-DAG: @_ZN5test312_GLOBAL__N_11CD1Ev = alias internal {{.*}} @_ZN5test312_GLOBAL__N_11CD2Ev
-// CHECK-DAG: @_ZN6PR752617allocator_derivedD1Ev = alias weak_odr void (%"struct.PR7526::allocator_derived"*)* @_ZN6PR752617allocator_derivedD2Ev
 
 struct A {
   int a;
@@ -45,6 +44,9 @@ namespace PR7526 {
   // CHECK: call void @__cxa_call_unexpected
   allocator::~allocator() throw() { foo(); }
 
+  // CHECK-LABEL: define void @_ZN6PR75263fooEv()
+  // CHECK: call void @_ZN6PR752617allocator_derivedD2Ev
+
   void foo() {
     allocator_derived ad;
   }