Index: lib/CodeGen/CGBuiltin.cpp =================================================================== --- lib/CodeGen/CGBuiltin.cpp +++ lib/CodeGen/CGBuiltin.cpp @@ -389,9 +389,14 @@ Value *ArgValue = EmitScalarExpr(E->getArg(0)); llvm::Type *ArgType = ArgValue->getType(); - Value *FnExpect = CGM.getIntrinsic(Intrinsic::expect, ArgType); Value *ExpectedValue = EmitScalarExpr(E->getArg(1)); + // Don't generate llvm.expect on -O0 as the backend won't use it for + // anything. + // Note, we still IRGen ExpectedValue because it could have side-effects. + if (CGM.getCodeGenOpts().OptimizationLevel == 0) + return RValue::get(ArgValue); + Value *FnExpect = CGM.getIntrinsic(Intrinsic::expect, ArgType); Value *Result = Builder.CreateCall2(FnExpect, ArgValue, ExpectedValue, "expval"); return RValue::get(Result); Index: test/CodeGen/builtin-expect.c =================================================================== --- test/CodeGen/builtin-expect.c +++ test/CodeGen/builtin-expect.c @@ -1,10 +1,14 @@ // RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s +// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O0 | FileCheck %s --check-prefix=CHECK_O0 int x; int y(void); void foo(); void FUNC() { +// CHECK-LABEL: define void @FUNC() // CHECK: [[call:%.*]] = call i32 @y +// CHECK_O0: [[call:%.*]] = call i32 @y +// CHECK_O0-NOT: call i64 @llvm.expect if (__builtin_expect (x, y())) foo (); } @@ -17,21 +21,25 @@ (void) __builtin_expect((isigprocmask(), 0), bar()); } +// CHECK-LABEL: define i32 @main() // CHECK: call void @isigprocmask() // CHECK: [[C:%.*]] = call i64 (...)* @bar() +// CHECK_O0: call void @isigprocmask() +// CHECK_O0: [[C:%.*]] = call i64 (...)* @bar() +// CHECK_O0-NOT: call i64 @llvm.expect -// CHECK: @test1 +// CHECK-LABEL: define i32 @test1 int test1(int x) { -// CHECK: @llvm.expect +// CHECK_O0-NOT: call i64 @llvm.expect if (__builtin_expect (x, 1)) return 0; return x; } -// CHECK: @test2 +// CHECK: define i32 @test2 int test2(int x) { -// CHECK: @llvm.expect +// CHECK_O0-NOT: call i64 @llvm.expect switch(__builtin_expect(x, 5)) { default: return 0;