Cold attribute on function decls are lost. Fix the problem

[davidxl]

Summary

LLVM static branch prediction depends on cold attribute to annotate branch probability. This is currently not possible for cold function decls as the information is dropped by FE.

This patch attaches the attributes to the callsite as noReturn. Another way is to pass the attribute to the function decl.

Also need suggestions on how to add a clang test case.

[davidxl]

Add a test case.

[rsmith]

LGTM

cfe/trunk/lib/CodeGen/CGCall.cpp

void CodeGenModule::ConstructAttributeList(
   // FIXME: handle sseregparm someday...
   if (TargetDecl) {
     if (TargetDecl->hasAttr<ReturnsTwiceAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::ReturnsTwice);
     if (TargetDecl->hasAttr<NoThrowAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
     if (TargetDecl->hasAttr<NoReturnAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
+    if (TargetDecl->hasAttr<ColdAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::Cold);
     if (TargetDecl->hasAttr<NoDuplicateAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::NoDuplicate);
     if (TargetDecl->hasAttr<ConvergentAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::Convergent);
 
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(
           getContext(), FuncAttrs, Fn->getType()->getAs<FunctionProtoType>());

cfe/trunk/test/CodeGen/attributes.c

 // CHECK: define hidden void @t4() [[NUW]] {
 void t4() __attribute__((visibility("hidden")));
 void t4() {}
 
 // CHECK: define void @t7() [[NR]] {
 void t7() __attribute__((noreturn, nothrow));
 void t7() { while (1) {} }
 
+// CHECK: define void @t72() [[COLDDEF:#[0-9]+]] {
+void t71(void) __attribute__((cold));
+void t72() __attribute__((cold));
+void t72() { t71(); }
+// CHECK: call void @t71() [[COLDSITE:#[0-9]+]]
+// CHECK: declare void @t71() [[COLDDECL:#[0-9]+]]
+
 // CHECK: define void @t10() [[NUW]] section "SECT" {
 void t10(void) __attribute__((section("SECT")));
 void t10(void) {}
 // CHECK: define void @t11() [[NUW]] section "SECT" {
 void __attribute__((section("SECT"))) t11(void) {}
 
 // CHECK: define i32 @t19() [[NUW]] {
 extern int t19(void) __attribute__((weak_import));

 // use the section in the definition.
 void __attribute__((section(".foo"))) t22(void);
 void __attribute__((section(".bar"))) t22(void) {}
 
 // CHECK: define void @t22() [[NUW]] section ".bar"
 
 // CHECK: attributes [[NUW]] = { noinline nounwind{{.*}} }
 // CHECK: attributes [[NR]] = { noinline noreturn nounwind{{.*}} }
+// CHECK: attributes [[COLDDEF]] = { cold {{.*}}}
+// CHECK: attributes [[COLDDECL]] = { cold {{.*}}}
+// CHECK: attributes [[COLDSITE]] = { cold {{.*}}}