IR: Make llvm.fake.use a DefaultAttrsIntrinsic (#131743)

This shouldn't be special and is just an ordinary sideeffect.

Author: arsenm

clang/test/CodeGen/fake-use-determinism.c

@@ -5,11 +5,11 @@
 // but that it remains the same between different test runs.
 
 // CHECK:      [[K_FAKE_USE:%[a-zA-Z0-9\.]+]] = load i32, ptr %k.addr
-// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[K_FAKE_USE]]) #2
+// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[K_FAKE_USE]])
 // CHECK-NEXT: [[J_FAKE_USE:%[a-zA-Z0-9\.]+]] = load i32, ptr %j.addr
-// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[J_FAKE_USE]]) #2
+// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[J_FAKE_USE]])
 // CHECK-NEXT: [[I_FAKE_USE:%[a-zA-Z0-9\.]+]] = load i32, ptr %i.addr
-// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[I_FAKE_USE]]) #2
+// CHECK-NEXT: call void (...) @llvm.fake.use(i32 [[I_FAKE_USE]])
 
 void bar();
 void foo(int i, int j, int k)

llvm/include/llvm/IR/Intrinsics.td

@@ -1881,7 +1881,8 @@ def int_is_constant : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_any_ty],
                                 "llvm.is.constant">;
 
 // Introduce a use of the argument without generating any code.
-def int_fake_use : Intrinsic<[], [llvm_vararg_ty]>;
+def int_fake_use : DefaultAttrsIntrinsic<[], [llvm_vararg_ty],
+  [IntrHasSideEffects, IntrInaccessibleMemOnly, IntrWillReturn]>;
 
 // Intrinsic to mask out bits of a pointer.
 // First argument must be pointer or vector of pointer. This is checked by the

llvm/test/CodeGen/AMDGPU/lower-kernargs.ll

@@ -1837,13 +1837,13 @@ attributes #2 = { nounwind "target-cpu"="tahiti" }
 !llvm.module.flags = !{!0}
 !0 = !{i32 1, !"amdhsa_code_object_version", i32 500}
 ;.
-; HSA: attributes #[[ATTR0:[0-9]+]] = { nounwind }
+; HSA: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
 ; HSA: attributes #[[ATTR1:[0-9]+]] = { nounwind "target-cpu"="kaveri" }
 ; HSA: attributes #[[ATTR2:[0-9]+]] = { nounwind "amdgpu-implicitarg-num-bytes"="40" "target-cpu"="kaveri" }
 ; HSA: attributes #[[ATTR3:[0-9]+]] = { nounwind "target-cpu"="tahiti" }
 ; HSA: attributes #[[ATTR4:[0-9]+]] = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
 ;.
-; MESA: attributes #[[ATTR0:[0-9]+]] = { nounwind }
+; MESA: attributes #[[ATTR0:[0-9]+]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite) }
 ; MESA: attributes #[[ATTR1:[0-9]+]] = { nounwind "target-cpu"="kaveri" }
 ; MESA: attributes #[[ATTR2:[0-9]+]] = { nounwind "amdgpu-implicitarg-num-bytes"="40" "target-cpu"="kaveri" }
 ; MESA: attributes #[[ATTR3:[0-9]+]] = { nounwind "target-cpu"="tahiti" }