Add __hlt intrinsic for Windows ARM. (#96578)

Add __hlt, which is a MSVC ARM64 intrinsic. 

This intrinsic is just the HLT instruction. MSVC's version seems to
return something undefined; in this patch
it will just return zero. 

MSVC intrinsics are defined here
https://learn.microsoft.com/en-us/cpp/intrinsics/arm64-intrinsics.
I used unsigned int as the return type, because that is what the MSVC
intrin.h header uses, even though
it conflicts with the documentation.

2 files changed, 14 insertions, 0 deletions

diff --git a/clang/test/CodeGen/arm64-microsoft-intrinsics.c b/clang/test/CodeGen/arm64-microsoft-intrinsics.c
index a354ed9..7953618 100644
--- a/clang/test/CodeGen/arm64-microsoft-intrinsics.c
+++ b/clang/test/CodeGen/arm64-microsoft-intrinsics.c
@@ -127,6 +127,15 @@ void check__break() {
 // CHECK-MSVC: call void @llvm.aarch64.break(i32 0)
 // CHECK-LINUX: error: call to undeclared function '__break'
 
+void check__hlt() {
+  __hlt(0);
+  __hlt(1, 2, 3, 4, 5);
+  int x = __hlt(0);
+}
+
+// CHECK-MSVC: call void @llvm.aarch64.hlt(i32 0)
+// CHECK-LINUX: error: call to undeclared function '__hlt'
+
 unsigned __int64 check__getReg(void) {
   unsigned volatile __int64 reg;
   reg = __getReg(18);
diff --git a/clang/test/Sema/builtins-microsoft-arm64.c b/clang/test/Sema/builtins-microsoft-arm64.c
index 6d0dc09..322cf75 100644
--- a/clang/test/Sema/builtins-microsoft-arm64.c
+++ b/clang/test/Sema/builtins-microsoft-arm64.c
@@ -9,6 +9,11 @@ void check__break(int x) {
   __break(x); // expected-error {{argument to '__break' must be a constant integer}}
 }
 
+void check__hlt() {
+  __hlt(-1); // expected-error-re {{argument value {{.*}} is outside the valid range}}
+  __hlt(65536); // expected-error-re {{argument value {{.*}} is outside the valid range}}
+}
+
 void check__getReg(void) {
   __getReg(-1); // expected-error-re {{argument value {{.*}} is outside the valid range}}
   __getReg(32); // expected-error-re {{argument value {{.*}} is outside the valid range}}