[clang] [llvm] [CodeGen][AArch64][FMV] PAC the stub_helper's frame on arm64e (PR #84704)

[Jon Roelofs via cfe-commits]

================
@@ -0,0 +1,58 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --function-signature --check-attributes --check-globals --include-generated-funcs
+// RUN: %clang_cc1 -triple arm64e-apple-ios -target-feature +ls64 -target-feature +fullfp16 -S -emit-llvm -o - %s | FileCheck %s
+
+int __attribute__((target_version("sha1"))) fmv(void) { return 1; }
+int __attribute__((target_version("default"))) fmv(void) { return 0; }
+int foo() {
+  return fmv();
+}
+
+//.
+// CHECK: @__aarch64_cpu_features = external dso_local global { i64 }
+// CHECK: @fmv.ifunc = weak_odr alias i32 (), ptr @fmv
+// CHECK: @fmv = weak_odr ifunc i32 (), ptr @fmv.resolver
+//.
+// CHECK: Function Attrs: noinline nounwind optnone
+// CHECK-LABEL: define {{[^@]+}}@fmv._Msha1
+// CHECK-SAME: () #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    ret i32 1
+//
+//
+// CHECK: Function Attrs: noinline nounwind optnone
+// CHECK-LABEL: define {{[^@]+}}@foo
+// CHECK-SAME: () #[[ATTR1:[0-9]+]] {
+// CHECK-NEXT:  entry:
+// CHECK-NEXT:    [[CALL:%.*]] = call i32 @fmv()
+// CHECK-NEXT:    ret i32 [[CALL]]
+//
+//
+// CHECK-LABEL: define {{[^@]+}}@fmv.resolver
+// CHECK-SAME: () #[[ATTR2:[0-9]+]] {
+// CHECK-NEXT:  resolver_entry:
+// CHECK-NEXT:    call void @__init_cpu_features_resolver()
+// CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
+// CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[TMP0]], 2048
+// CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[TMP1]], 2048
+// CHECK-NEXT:    [[TMP3:%.*]] = and i1 true, [[TMP2]]
+// CHECK-NEXT:    br i1 [[TMP3]], label [[RESOLVER_RETURN:%.*]], label [[RESOLVER_ELSE:%.*]]
+// CHECK:       resolver_return:
+// CHECK-NEXT:    ret ptr @fmv._Msha1
+// CHECK:       resolver_else:
+// CHECK-NEXT:    ret ptr @fmv.default
----------------
jroelofs wrote:

The thing that's missing is this:

https://github.com/apple/llvm-project/blob/970b6231f607e211c23e15a582572e6f18f4e6b2/clang/include/clang/CodeGen/CodeGenABITypes.h#L122-L126

along with this hunk:

```
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2893,7 +2893,11 @@ static void CreateMultiVersionResolverReturn(CodeGenModule &CGM,
                                              llvm::Function *FuncToReturn,
                                              bool SupportsIFunc) {
   if (SupportsIFunc) {
-    Builder.CreateRet(FuncToReturn);
+    llvm::Constant *Fn = FuncToReturn;
+    if (CGM.getContext().getTargetInfo().getTriple().isArm64e())
+      Fn = CGM.getConstantSignedPointer(
+          Fn, 0, nullptr, llvm::Constant::getNullValue(CGM.SizeTy));
+    Builder.CreateRet(Fn);
     return;
   }
 ```
 
 This arranges for the resolver to return signed function pointers. There is no difference for arm64(non-e).

https://github.com/llvm/llvm-project/pull/84704