yubing added inline comments.
================
Comment at: clang/lib/Headers/immintrin.h:301
+ unsigned long long tmp;
+ if (__builtin_ia32_rdrand32_step((unsigned int *)&tmp) &
+ __builtin_ia32_rdrand32_step(((unsigned int *)&tmp) + 1)) {
----------------
RKSimon wrote:
> RKSimon wrote:
> > craig.topper wrote:
> > > craig.topper wrote:
> > > > Should `&` be `&&`?
> > > Can we avoid the pointer cast here? Use two unsigned ints and manually
> > > concatenate them to a 64-bit value.
> > +1
> > ```
> > unsigned int lo, hi;
> > if (__builtin_ia32_rdrand32_step(&lo) &&
> > __builtin_ia32_rdrand32_step(&hi)) {
> > *p = ((unsigned long)hi << 32) | lo;
> > return 1;
> > }
> > ```
> Are there any sideeffects that we might encounter by not always performing
> both __builtin_ia32_rdrand32_step calls?
> ```
> unsigned int __lo, __hi;
> int __res_lo = __builtin_ia32_rdrand32_step(&__lo);
> int __res_hi = __builtin_ia32_rdrand32_step(&__hi);
> if (__res_lo && __res_hi) {
> *__p = ((unsigned long long)__hi << 32) | (unsigned long long)__lo;
> return 1;
> } else {
> *__p = 0;
> return 0;
> }
> ```
however, if the first rdrand32 failed, then we don't need to execute the second
one.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D132141/new/
https://reviews.llvm.org/D132141
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