[PATCH] D155145: [X86] Add AVX-VNNI-INT16 instructions.

[Phoebe Wang via Phabricator via llvm-commits]

pengfei added a comment.

In D155145#4556157 <https://reviews.llvm.org/D155145#4556157>, @anna wrote:

> In D155145#4554786 <https://reviews.llvm.org/D155145#4554786>, @anna wrote:
>
>>> Can you capture the values of EAX, EBX, ECX, and EDX after the two calls to getX86CpuIDAndInfoEx that have 0x7 as the first argument? Maybe there's a bug in CPUID on Sandy Bridge.
>>
>> Sure, on the original code before the patch you suggested right?
>> The two calls are:
>>
>>    bool HasLeaf7 =
>>           MaxLevel >= 7 && !getX86CpuIDAndInfoEx(0x7, 0x0, &EAX, &EBX, &ECX, &EDX);
>>   +   llvm::errs() << "Before setting fsgsbase the value for EAX: " << EAX
>>   +                     << " EBX: " << EBX << " ECX: " << ECX << "  EDX: " << EDX
>>   +                     << "\n";
>>     
>>       Features["fsgsbase"]   = HasLeaf7 && ((EBX >>  0) & 1);
>>   ....
>>   bool HasLeaf7Subleaf1 =
>>           MaxLevel >= 7 && !getX86CpuIDAndInfoEx(0x7, 0x1, &EAX, &EBX, &ECX, &EDX);
>>   +   llvm::errs() << "Before setting sha512 the value for EAX: " << EAX
>>   +                     << " EBX: " << EBX << " ECX: " << ECX << "  EDX: " << EDX
>>   +                     << "\n";
>>       Features["sha512"]     = HasLeaf7Subleaf1 && ((EAX >> 0) & 1);
>>   ...
>>   we set avxvnniint16 after this
>>
>> Takes a while to get a build on this machine, should have the output soon.
>
> @craig.topper here is the output:
>
>   Before setting fsgsbase the value for EAX: 0 EBX: 0 ECX: 0  EDX: 2617246720 // this is after the HasLeaf7 calculation
>   Before setting sha512 the value for EAX: 0 EBX: 0 ECX: 0  EDX: 2617246720 // this is after the HasLeaf7Subleaf1 calculation
>
> So, with your patch `HasLeaf7Subleaf1` is 0 as EAX is 0. Pls let me know if you need  any additional diagnostics output (we actually lose access to the machine on friday, since it is being retired!).
>
>> The documentation says that invalid subleaves of leaf 7 should return all 0s. So we thought it was safe to check the bits of sub leaf 1 even if eax from subleaf 0 doesn't say subleaf 1 is supported.
>
> This means the CPUID doesn't satisfy the documentation since EDX != 0 for SubLeaf1?

The identical EDX value looks dubious to me. Could you compile and run above code and paste the result here? Thanks!


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https://reviews.llvm.org/D155145