[PATCH] D75723: [X86] Enable intrinsics _BitScan*

Tue Mar 10 22:17:02 PDT 2020

skan added inline comments.

================
Comment at: clang/lib/Headers/ia32intrin.h:456
+  __extension__({                                                              \
+    long long c = (long long)(b);                                              \
+    unsigned char d;                                                           \
----------------
craig.topper wrote:
> Variable name in macro needs to start with 2 underscores to avoid conflicts with user variable names. I need to think about whether that’s enough to avoid problems.
The variable shadowing problem when using statement expression is a known issue. 

https://patches-gcc.linaro.org/patch/17303/
https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html

 In general, user variable names should not start with  2 underscores, so I think it's safe enough. 

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75723/new/

https://reviews.llvm.org/D75723