[MS] Crush when calling intrinsic __cpuid

[phoebewang]

Bugzilla Link	50133
Resolution	FIXED
Resolved on	Apr 29, 2021 19:25
Version	trunk
OS	Windows NT
CC	@topperc,@RKSimon,@phoebewang,@rnk,@rotateright
Fixed by commit(s)	https://reviews.llvm.org/rGe0c7db7d8ce780df5129b4d0f5bbf145271ef14f

Extended Description

Small reproducer:

#include
#include
#include <intrin.h>

struct A {
std::string S;
std::vector<std::array<int, 4>> V;
A() {
std::array<int, 4> B;
__cpuid(B.data(), 0);
V.push_back(B);
V.push_back(B);
char C[64];
memset(C, 0, sizeof(C));
S = C;
}
} T;

Commands:

clang-cl -mavx2 /EHs repro.cpp -S
cat repro.asm | grep cpuid -A7
cpuid
#NO_APP
mov r11d, eax
mov rax, qword ptr [rbx + 72] # 8-byte Reload
mov r10d, ebx
mov r9d, ecx
mov rcx, qword ptr [rbx + 80] # 8-byte Reload
mov r8d, edx

[phoebewang]

As far as my observation, we didn't consider if the frame pointer RBX will be clobbered by inline asm.
I have no idea if we can fix this problem in frame lowering completely.
Given usage of inline asm is rare on Windows, especially MSVC doesn't support for 64 bits. I think a workaround should be good for a quick fix.
Candidate patch: https://reviews.llvm.org/D101338

[rnk]

This is basically an instance of the more general problem, llvm.org/pr16830, which has been known for a while. In this case, I think a workaround makes sense.

[phoebewang]

Thanks for the information.