[Bug tree-optimization/93354] New: [10 Regression] Bogus remove of redundant store

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93354

            Bug ID: 93354
           Summary: [10 Regression] Bogus remove of redundant store
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

We are currently removing the store to *z as redundant as part of VN for

typedef __INT32_TYPE__ int32_t;
typedef __INT64_TYPE__ int64_t;
struct X { int32_t i; int32_t j; };
void foo (int64_t *z)
{
  ((struct X *)z)->i = 0x05060708;
  ((struct X *)z)->j = 0x01020304;
  *z = 0x0102030405060708;
}

int main()
{
  int64_t l = 0;
  int64_t *p;
  asm ("" : "=r" (p) : "0" (&l));
  foo (p);
  if (l != 0x0102030405060708)
    __builtin_abort ();
  return 0;
}

there's some obfuscation needed to make our conservative allowance of
punning not to trigger (we must hide the must-alias of the definitions
via struct X).