[PATCH] D42574: [ARM] Lower lower saturate to 0 and lower saturate to -1 using bit-operations

[Yvan Roux via llvm-commits]

On 1 February 2018 at 00:00, Evgenii Stepanov via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:
> eugenis added a comment.
>
> I've reverted your commit in r323929.
> It miscompiles the following program on armv7-linux-android:
> #include <stdio.h>
>
> typedef unsigned long long u64;
> typedef signed long long s64;
> s64 f(u64 x) {
>
>   return (x > (u64)0x7fffffffffffffffULL) ? (s64)1 : -(s64)x;
>
> }
>
> int main() {
>
>   volatile u64 x = 42;
>   s64 y = f(x);
>   printf("%lld\n", y);
>
> }
>
> Without this patch, the output is -42.
> With your patch, the output is 4294967254.
>
> It also breaks the android bot:
>
>   http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-android/builds/7279

Thanks Evgenii, you were faster than me ;)

>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D42574
>
>
>
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