Do not generate LLVM IR for available_externally function bodies at

-O0, since we won't be using the definitions for anything anyway. For
lib/System/Path.o when built in Debug+Asserts mode, this leads to a 4%
improvement in compile time (and suppresses 440 function bodies).

<rdar://problem/7987644>

llvm-svn: 108156

clang/lib/CodeGen/CodeGenModule.cpp

@@ -817,14 +817,22 @@ void CodeGenModule::EmitGlobalDefinition(GlobalDecl GD) {
     if (Method->isVirtual())
       getVTables().EmitThunks(GD);
 
-  if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(D))
-    return EmitCXXConstructor(CD, GD.getCtorType());
+  if (const FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
+    // At -O0, don't generate IR for functions with available_externally 
+    // linkage.
+    if (CodeGenOpts.OptimizationLevel == 0 &&
+        getFunctionLinkage(Function) 
+                                  == llvm::Function::AvailableExternallyLinkage)
+      return;
+    
+    if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(Function))
+      return EmitCXXConstructor(CD, GD.getCtorType());
   
-  if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(D))
-    return EmitCXXDestructor(DD, GD.getDtorType());
+    if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(Function))
+      return EmitCXXDestructor(DD, GD.getDtorType());
 
-  if (isa<FunctionDecl>(D))
     return EmitGlobalFunctionDefinition(GD);
+  }
   
   if (const VarDecl *VD = dyn_cast<VarDecl>(D))
     return EmitGlobalVarDefinition(VD);

clang/test/CXX/temp/temp.spec/temp.explicit/p9-linkage.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm -std=c++0x -o - %s | FileCheck %s
+// RUN: %clang_cc1 -O1 -emit-llvm -std=c++0x -o - %s | FileCheck %s
 
 template<typename T>
 struct X0 {

clang/test/CodeGen/available-externally-suppress.c

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -emit-llvm -o - -O0 -triple x86_64-apple-darwin10 %s | FileCheck %s
+
+// Ensure that we don't emit available_externally functions at -O0.
+int x;
+
+inline void f0(int y) { x = y; }
+
+// CHECK: define void @test()
+// CHECK: declare void @f0(i32)
+void test() {
+  f0(17);
+}

clang/test/CodeGen/inline.c

@@ -1,5 +1,5 @@
 // RUN: echo "GNU89 tests:"
-// RUN: %clang %s -emit-llvm -S -o %t -std=gnu89
+// RUN: %clang %s -O1 -emit-llvm -S -o %t -std=gnu89
 // RUN: grep "define available_externally i32 @ei()" %t
 // RUN: grep "define i32 @foo()" %t
 // RUN: grep "define i32 @bar()" %t
@@ -14,7 +14,7 @@
 // RUN: grep "define available_externally i32 @test5" %t
 
 // RUN: echo "\nC99 tests:"
-// RUN: %clang %s -emit-llvm -S -o %t -std=c99
+// RUN: %clang %s -O1 -emit-llvm -S -o %t -std=c99
 // RUN: grep "define i32 @ei()" %t
 // RUN: grep "define available_externally i32 @foo()" %t
 // RUN: grep "define i32 @bar()" %t
@@ -29,7 +29,7 @@
 // RUN: grep "define available_externally i32 @test5" %t
 
 // RUN: echo "\nC++ tests:"
-// RUN: %clang %s -emit-llvm -S -o %t -std=c++98
+// RUN: %clang %s -O1 -emit-llvm -S -o %t -std=c++98
 // RUN: grep "define linkonce_odr i32 @_Z2eiv()" %t
 // RUN: grep "define linkonce_odr i32 @_Z3foov()" %t
 // RUN: grep "define i32 @_Z3barv()" %t

clang/test/CodeGen/inline2.c

@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -std=gnu89 -triple i386-apple-darwin9 -emit-llvm %s -o - | FileCheck -check-prefix GNU89 %s
-// RUN: %clang_cc1 -std=c99 -triple i386-apple-darwin9 -emit-llvm %s -o - | FileCheck -check-prefix C99 %s
+// RUN: %clang_cc1 -O1 -std=gnu89 -triple i386-apple-darwin9 -emit-llvm %s -o - | FileCheck -check-prefix GNU89 %s
+// RUN: %clang_cc1 -O1 -std=c99 -triple i386-apple-darwin9 -emit-llvm %s -o - | FileCheck -check-prefix C99 %s
 
 // CHECK-GNU89: define i32 @f0()
 // CHECK-C99: define i32 @f0()

clang/test/CodeGenCXX/template-instantiation.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -O1 -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
 
 // CHECK-NOT: @_ZTVN5test118stdio_sync_filebufIwEE = constant
 // CHECK-NOT: _ZTVN5test315basic_fstreamXXIcEE

clang/test/CodeGenCXX/visibility-hidden-extern-templates.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm -o - -fvisibility hidden %s | FileCheck %s
+// RUN: %clang_cc1 -O1 -emit-llvm -o - -fvisibility hidden %s | FileCheck %s
 
 template<typename T>
 struct X {