[Bug tree-optimization/93843] New: wrong code at -O3 on x86_64-linux-gnu

qrzhang at gatech dot edu gcc-bugzilla@gcc.gnu.org
Thu Feb 20 06:07:00 GMT 2020


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93843

            Bug ID: 93843
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qrzhang at gatech dot edu
  Target Milestone: ---

A recent regression. Gcc-9 works fine.

Bisection points to g:6271dd984d7f920d4fb17ad37af6a1f8e6b796dc

$ gcc-trunk -v
gcc version 10.0.1 20200219 (experimental) [master revision
665c5bad168:533e82edecf:51faf07cef9293af544bfacc7d0b320ab90d7d60] (GCC)


$ gcc-trunk -O3 abc.c ; ./a.out
4
0

$ gcc-9 -O3 abc.c ; ./a.out
4
4

$ gcc-trunk  abc.c ; ./a.out
4
4

$ cat abc.c
int printf(const char *, ...);
char a, e;
struct {
  short b;
  short c;
} d;
int f;
int main() {
  short *g = &d.c, *h = &d.b;
  e = 4 - a;
  *h = *g = e;
  for (; f < 2; f++)
    printf("%d\n", d.c);
}


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