[PATCH] D86547: [compiler-rt][builtins] Use c[tl]zsi macro instead of __builtin_c[tl]z

[Ayke via Phabricator via cfe-commits]

aykevl added inline comments.


================
Comment at: compiler-rt/lib/builtins/fp_extend.h:32-39
 #if defined __LP64__
   return __builtin_clzl(a);
 #else
   if (a & REP_C(0xffffffff00000000))
-    return __builtin_clz(a >> 32);
+    return clzsi(a >> 32);
   else
+    return 32 + clzsi(a & REP_C(0xffffffff));
----------------
aykevl wrote:
> Perhaps more reliable would be the following:
> 
> ```
> #if ULONG_MAX == 0xFFFFFFFFFFFFFFFF
>   return __builtin_clzl(a);
> #elif ULLONG_MAX == 0xFFFFFFFFFFFFFFFF
>   return __builtin_clzll(a);
> #else
>   #error Unsupported platform
> #endif
> ```
> 
> This is what I've also used in int_types.h to detect clzsi etc. It probably would need to be tested on some more architectures though (32 and 64 bit).
In fact, it might be possible to use `__builtin_clzll` for all platforms (it maps to 'long long', which I think is 64-bit practically everywhere).


Repository:
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  https://reviews.llvm.org/D86547/new/

https://reviews.llvm.org/D86547