[AArch64] Mark aarch64_set_fpmr as IntrWriteMem (#146353)

llvm.aarch64.set.fpmr only writes to inaccessible memory. Tag it with
the IntrWriteMem and IntrInaccessibleMemOnly properties so the optimiser
can treat it as a pure write.

The original patch did not add this property, causing the intrinsic to
be conservatively treated as readwrite. This commit fixes that.

Author: CarolineConcatto

clang/test/CodeGen/AArch64/attr-fp8-function.c

@@ -0,0 +1,37 @@
+// Check memory attribute for FP8 function
+
+// REQUIRES: aarch64-registered-target
+
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -target-feature +neon -target-feature +fp8 -target-feature +sve -target-feature +sme -target-feature +sme2 -target-feature +sme-f8f16 -target-feature +sme-f8f32  -target-feature +ssve-fp8fma -disable-O0-optnone -Werror -Wall -emit-llvm -o - %s | FileCheck %s
+
+#include <arm_neon.h>
+#include <arm_sme.h>
+
+
+// SIMD
+mfloat8x16_t test_vcvtq_mf8_f16_fpm(float16x8_t vn, float16x8_t vm, fpm_t fpm) {
+  return vcvtq_mf8_f16_fpm(vn, vm, fpm);
+}
+
+// SVE
+svfloat16_t test_svcvtlt2_f16_mf8(svmfloat8_t zn, fpm_t fpm) __arm_streaming {
+  return svcvtlt2_f16_mf8_fpm(zn, fpm);
+}
+
+// CHECK: declare void @llvm.aarch64.set.fpmr(i64) [[ATTR3:#.*]]
+// CHECK: declare <vscale x 8 x half> @llvm.aarch64.sve.fp8.cvtlt2.nxv8f16(<vscale x 16 x i8>) [[ATTR4:#.*]]
+
+
+// SME
+svfloat32_t test_svmlalltt_lane_f32_mf8(svfloat32_t zda, svmfloat8_t zn, svmfloat8_t zm, fpm_t fpm) __arm_streaming {
+  return svmlalltt_lane_f32_mf8_fpm(zda, zn, zm, 7, fpm);
+}
+
+// CHECK: declare <vscale x 4 x float> @llvm.aarch64.sve.fp8.fmlalltt.lane.nxv4f32(<vscale x 4 x float>, <vscale x 16 x i8>, <vscale x 16 x i8>, i32 immarg) [[ATTR4]]
+
+// CHECK: declare <16 x i8> @llvm.aarch64.neon.fp8.fcvtn.v16i8.v8f16(<8 x half>, <8 x half>) [[ATTR4]]
+
+// CHECK: attributes [[ATTR1:#.*]] = {{{.*}}} 
+// CHECK: attributes [[ATTR2:#.*]] = {{{.*}}}
+// CHECK: attributes [[ATTR3]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: write) }
+// CHECK: attributes [[ATTR4]] = { nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: read) }

llvm/include/llvm/IR/IntrinsicsAArch64.td

@@ -761,7 +761,7 @@ let TargetPrefix = "aarch64" in {
   class RNDR_Intrinsic
     : DefaultAttrsIntrinsic<[llvm_i64_ty, llvm_i1_ty], [], [IntrNoMem, IntrHasSideEffects]>;
   class FPMR_Set_Intrinsic
-    : DefaultAttrsIntrinsic<[], [llvm_i64_ty], [IntrInaccessibleMemOnly]>; 
+    : DefaultAttrsIntrinsic<[], [llvm_i64_ty], [IntrWriteMem, IntrInaccessibleMemOnly]>;
 }
 
 // FP environment registers.