Bugzilla Link	42833
Resolution	FIXED
Resolved on	Aug 20, 2019 03:10
Version	trunk
OS	Linux
Blocks	#41819
CC	@dbabokin,@topperc,@zmodem,@RKSimon,@regehr,@rotateright,@Vsevolod-Livinskij
Fixed by commit(s)	r367412,r367429

Extended Description

Clang produces incorrect result with -O3 -march=skx

Reproducer:
#include <stdio.h>

int b;
unsigned c[49];
int d[49];

void i() {
for (int g = 32; g <= 48; g++) {
d[g] -= c[g] + b;
c[g] += c[g] + b;
b -= b;
}
}

int main() {
for (int g = 0; g < 49; ++g)
c[g] = 3;
i();
printf("%d\n", d[36]);
}

Error:

$ clang -O3 -march=skx small.c ; ./a.out
0
$ clang -O0 -march=skx small.c ; ./a.out
-3

LLVM version:
clang version 10.0.0 (trunk 367162)
Target: x86_64-unknown-linux-gnu
Thread model: posix