[PATCH] D75723: [X86] Enable intrinsics _BitScan*
Craig Topper via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Wed Mar 11 00:09:25 PDT 2020
craig.topper added inline comments.
================
Comment at: clang/lib/Headers/ia32intrin.h:421
+ if (__c != 0) { \
+ *(a) = (unsigned)__bsfd(__c); \
+ __d = 1; \
----------------
skan wrote:
> craig.topper wrote:
> > Should (a) have a cast to (unsigned *)?
> No. Using a cast here may cause pointer aliasing problem.
>
> https://stackoverflow.com/questions/98650/what-is-the-strict-aliasing-rule
>
> If a is not `unsigned *`, letting the compiler do auto integer conversion for `*(a)` is the correct way, from my perspective.
But if we implemented this as an inline function instead of a macro wouldn't the argument have been an unsigned *?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D75723/new/
https://reviews.llvm.org/D75723
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