[MS] Preserve base register %rbx around cpuid

[pengfei]

Summary

This patch copies implementation from cpuid.h, which preserve base register %rbx around cpuid. It fixes PR50133.

[pengfei]

Update for test.

[craig.topper]

If I remember correctly cpuid.h implementation handles this. Can we copy that?

[pengfei]

Yes, it is a pretty implementation. Thanks Craig.

[rnk]

Seems reasonable, thanks.

We really ought to solve the general problem one day. It is kind of pig-headed that the backend just picks two arbitrary CSRs, the base and frame pointers, and doesn't bother checking if any instructions clobber those registers.

[pengfei]

In D101338#2726759, @rnk wrote:

Seems reasonable, thanks.

We really ought to solve the general problem one day. It is kind of pig-headed that the backend just picks two arbitrary CSRs, the base and frame pointers, and doesn't bother checking if any instructions clobber those registers.

Agreed. Thanks Reid.

clang/lib/Headers/intrin.h

__asm__ __volatile__("rep stosq" : "+D"(__dst), "+c"(__n) : "a"(__x)
                        : "memory");
 }
 #endif
 
 /*----------------------------------------------------------------------------*\
 |* Misc
 \*----------------------------------------------------------------------------*/
 #if defined(__i386__) || defined(__x86_64__)
-static __inline__ void __DEFAULT_FN_ATTRS __cpuid(int __info[4], int __level) {
+static void __attribute__((noinline, __nodebug__)) __cpuid(int __info[4], int __level) {
   __asm__("cpuid"
           : "=a"(__info[0]), "=b"(__info[1]), "=c"(__info[2]), "=d"(__info[3])
           : "a"(__level), "c"(0));
 }
-static __inline__ void __DEFAULT_FN_ATTRS __cpuidex(int __info[4], int __level,
+static void __attribute__((noinline, __nodebug__)) __cpuidex(int __info[4], int __level,
                                                     int __ecx) {
   __asm__("cpuid"
           : "=a"(__info[0]), "=b"(__info[1]), "=c"(__info[2]), "=d"(__info[3])
           : "a"(__level), "c"(__ecx));
 }
 static __inline__ void __DEFAULT_FN_ATTRS __halt(void) {
   __asm__ volatile("hlt");
 }

clang/test/CodeGen/ms-intrinsics-cpuid.c

 // RUN: %clang_cc1 -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
 // RUN:         -triple i686-windows-msvc -emit-llvm %s -o - | FileCheck %s
 // RUN: %clang_cc1 -ffreestanding -fms-extensions -fms-compatibility -fms-compatibility-version=17.00 \
 // RUN:         -triple x86_64-windows-msvc -emit-llvm %s -o - | FileCheck %s
 
 // intrin.h needs size_t, but -ffreestanding prevents us from getting it from
 // stddef.h.  Work around it with this typedef.
 typedef __SIZE_TYPE__ size_t;
 
 #include <intrin.h>
 
 void test__cpuid(int *info, int level) {
   __cpuid(info, level);
 }
-// CHECK-LABEL: define {{.*}} @test__cpuid(i32* %{{.*}}, i32 %{{.*}})
+// CHECK-LABEL: define {{.*}} @__cpuid(i32* %{{.*}}, i32 %{{.*}})
 // CHECK: call { i32, i32, i32, i32 } asm "cpuid",
 // CHECK-SAME:   "={ax},={bx},={cx},={dx},{ax},{cx},~{dirflag},~{fpsr},~{flags}"
 // CHECK-SAME:   (i32 %{{.*}}, i32 0)
+
+// CHECK-LABEL: define {{.*}} @__cpuidex(i32* %{{.*}}, i32 %{{.*}}, i32 %{{.*}})
+// CHECK: call { i32, i32, i32, i32 } asm "cpuid",
+// CHECK-SAME:   "={ax},={bx},={cx},={dx},{ax},{cx},~{dirflag},~{fpsr},~{flags}"
+// CHECK-SAME:   (i32 %{{.*}}, i32 %{{.*}})
+
+// CHECK-LABEL: define {{.*}} @test__cpuid(i32* %{{.*}}, i32 %{{.*}})
+// CHECK: call void @__cpuid(i32* %{{.*}}, i32 %{{.*}})