[PATCH] D88712: [CGBuiltin] Respect asm labels and redefine_extname for builtins with specialized emitting

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D88712#2412874 <https://reviews.llvm.org/D88712#2412874>, @venkataramanan.kumar.llvm wrote:

> In D88712#2412366 <https://reviews.llvm.org/D88712#2412366>, @MaskRay wrote:
>
>> In D88712#2411841 <https://reviews.llvm.org/D88712#2411841>, @venkataramanan.kumar.llvm wrote:
>>
>>> 
>>
>> For your example:
>>
>>   extern double log (double) asm ("" "log_finite") __attribute__ ((nothrow));
>>   
>>   double mylog (double d) { return log(d); }
>>
>> The intention is to emit `log_finite`, no matter the `-ffast-math`. Both GCC and Clang (after this patch) emit `jmp log_finite`.
>>
>> The previous behavior (according to your comment, with an older glibc) was undesired. So I think the right suggestion is to upgrade glibc.
>
> Then there optimizations like vectorization, inst combine which works on the LLVM intrinsics.  But they will be not happening now  with  log_finite calls.  
> is it possible to add an option to disable this feature, in case anyone who wants to avail these optimization?

I lean toward not adding an option since newer glibc does not have the problem (and the new Clang behavior is consistent with GCC).


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