Add support for __attribute__((hot)) and __attribute__((cold)).

Currently cold functions are marked with the "optsize" attribute in CodeGen
so they are always optimized for size.  The hot attribute is just ignored,
LLVM doesn't have a way to express hotness at the moment.

llvm-svn: 156723

clang/include/clang/Basic/Attr.td

@@ -243,6 +243,10 @@ def Cleanup : InheritableAttr {
   let Args = [FunctionArgument<"FunctionDecl">];
 }
 
+def Cold : InheritableAttr {
+  let Spellings = ["cold"];
+}
+
 def Common : InheritableAttr {
   let Spellings = ["common"];
 }
@@ -348,6 +352,10 @@ def GNUInline : InheritableAttr {
   let Spellings = ["gnu_inline"];
 }
 
+def Hot : InheritableAttr {
+  let Spellings = ["hot"];
+}
+
 def IBAction : InheritableAttr {
   let Spellings = ["ibaction"];
 }

clang/lib/CodeGen/CodeGenModule.cpp

@@ -523,6 +523,10 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
       !F->hasFnAttr(llvm::Attribute::NoInline))
     F->addFnAttr(llvm::Attribute::AlwaysInline);
 
+  // FIXME: Communicate hot and cold attributes to LLVM more directly.
+  if (D->hasAttr<ColdAttr>())
+    F->addFnAttr(llvm::Attribute::OptimizeForSize);
+
   if (isa<CXXConstructorDecl>(D) || isa<CXXDestructorDecl>(D))
     F->setUnnamedAddr(true);
 

clang/lib/Sema/SemaDeclAttr.cpp

@@ -1294,6 +1294,46 @@ static void handleAliasAttr(Sema &S, Decl *D, const AttributeList &Attr) {
                                          Str->getString()));
 }
 
+static void handleColdAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  // Check the attribute arguments.
+  if (!checkAttributeNumArgs(S, Attr, 0))
+    return;
+
+  if (!isa<FunctionDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+      << Attr.getName() << ExpectedFunction;
+    return;
+  }
+
+  if (D->hasAttr<HotAttr>()) {
+    S.Diag(Attr.getLoc(), diag::err_attributes_are_not_compatible)
+      << Attr.getName() << "hot";
+    return;
+  }
+
+  D->addAttr(::new (S.Context) ColdAttr(Attr.getRange(), S.Context));
+}
+
+static void handleHotAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  // Check the attribute arguments.
+  if (!checkAttributeNumArgs(S, Attr, 0))
+    return;
+
+  if (!isa<FunctionDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+      << Attr.getName() << ExpectedFunction;
+    return;
+  }
+
+  if (D->hasAttr<ColdAttr>()) {
+    S.Diag(Attr.getLoc(), diag::err_attributes_are_not_compatible)
+      << Attr.getName() << "cold";
+    return;
+  }
+
+  D->addAttr(::new (S.Context) HotAttr(Attr.getRange(), S.Context));
+}
+
 static void handleNakedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   // Check the attribute arguments.
   if (!checkAttributeNumArgs(S, Attr, 0))
@@ -3825,6 +3865,8 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_ownership_takes:
   case AttributeList::AT_ownership_holds:
       handleOwnershipAttr     (S, D, Attr); break;
+  case AttributeList::AT_cold:        handleColdAttr        (S, D, Attr); break;
+  case AttributeList::AT_hot:         handleHotAttr         (S, D, Attr); break;
   case AttributeList::AT_naked:       handleNakedAttr       (S, D, Attr); break;
   case AttributeList::AT_noreturn:    handleNoReturnAttr    (S, D, Attr); break;
   case AttributeList::AT_nothrow:     handleNothrowAttr     (S, D, Attr); break;

clang/test/CodeGen/attr-coldhot.c

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+int test1() __attribute__((__cold__)) {
+  return 42;
+
+// Check that we set the optsize attribute on the function.
+// CHECK: @test1{{.*}}optsize
+// CHECK: ret
+}

clang/test/Sema/attr-coldhot.c

@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+int foo() __attribute__((__hot__));
+int bar() __attribute__((__cold__));
+
+int var1 __attribute__((__cold__)); // expected-warning{{'__cold__' attribute only applies to functions}}
+int var2 __attribute__((__hot__)); // expected-warning{{'__hot__' attribute only applies to functions}}
+
+int qux() __attribute__((__hot__)) __attribute__((__cold__)); // expected-error{{'__hot__' and cold attributes are not compatible}}
+int baz() __attribute__((__cold__)) __attribute__((__hot__)); // expected-error{{'__cold__' and hot attributes are not compatible}}