[Bug middle-end/102386] New: [12 regression] bogus -Wrestrict for unreachable memcpy()

[dimhen at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102386

            Bug ID: 102386
           Summary: [12 regression] bogus -Wrestrict for unreachable
                    memcpy()
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dimhen at gmail dot com
  Target Milestone: ---

r12-3456 PASS
r12-3545 FAIL

$ cat x.i
static int GetHashParam_HP_OPAQUEBLOB_pdwDataLen = 0;
void *memcpy(void *, const void *, unsigned long);
typedef struct {
  int tSimpleBlobHeader;
  int bCurrKey[];
} CRYPT_OPAQUEHASHBLOB;
int GetHashParam_HP_OPAQUEBLOB() {
  CRYPT_OPAQUEHASHBLOB *pBlb;
  if (GetHashParam_HP_OPAQUEBLOB_pdwDataLen) {
    void *pcn = pBlb->bCurrKey, *pdwBuff = pBlb->bCurrKey;
    int dwDWBufLen = 8;
    memcpy(pcn, pdwBuff, sizeof(1) * dwDWBufLen);
  }
  return 1;
}

$ gcc -fpreprocessed -O --param max-early-inliner-iterations=2 -Wrestrict -c
x.i
x.i: In function 'GetHashParam_HP_OPAQUEBLOB':
x.i:12:5: warning: 'memcpy' accessing 32 bytes at offsets 4 and 4 overlaps 32
bytes at offset 4 [-Wrestrict]
   12 |     memcpy(pcn, pdwBuff, sizeof(1) * dwDWBufLen);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Test extracted from private codebase.
Key part:

static inline void foo(void *p, void *q, int N)
{
   if(p != q)
     memcpy(p, q, N);
}

void bar(void q, void p, int N)
{
   foo(p, q, N);
}