[Bug tree-optimization/90373] New: Better alias analysis based on libc functions with arguments which cannot alias

[david.bolvansky at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90373

            Bug ID: 90373
           Summary: Better alias analysis based on libc functions with
                    arguments which cannot alias
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david.bolvansky at gmail dot com
  Target Milestone: ---

bool foo(int *a, int *b, unsigned n) {
    memcpy(a, b, n);
    return a == b;
}

GCC trunk X86-64 -O3
foo(int*, int*, unsigned int):
        push    rbx
        mov     edx, edx
        mov     rbx, rsi
        call    memcpy
        cmp     rax, rbx
        pop     rbx
        sete    al
        ret

if a and b aliases, it would be UB to call memcpy since "The memory areas must
not overlap.". Currently GCC emits "a == b", but possibly, info that a cannot
alias b in range n could be propagated more.


Same for strcpy
"The strings may not overlap, and the destination string dest must be large
enough to receive the copy."