[libc-commits] [PATCH] D117584: [libc] Specialize portion of hypot for x86_64 CPUs.

[Siva Chandra via Phabricator via libc-commits]

sivachandra added inline comments.


================
Comment at: libc/src/__support/x86_64/find_leading_one.h:28-31
+  __asm__("bsr %[value], %[value]"
+          : [value] "=r"(value)
+          : "0"(value)
+          : "flags"); // Clobbers ZF
----------------
cratonica wrote:
> sivachandra wrote:
> > It seems to me like one can use `__builtin_clz` and avoid target assembly? For example: https://godbolt.org/z/eY8n8P118
> Nice, that also works for ARM: https://godbolt.org/z/bY9nfEd16
> 
> Are we OK using such builtins in this library ? If so, should we get rid of the original find_leading_one() function altogether and just call __builtin_clz ? Or should it still be specialized for each architecture and delegate at that level?
Yes, it is OK to use compiler builtins for this use case. We can get rid of the original `find_leading_one`.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D117584/new/

https://reviews.llvm.org/D117584