[Bug middle-end/124261] New: Memory read disambiguated by clang but not by gcc

[hubicka at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124261

            Bug ID: 124261
           Summary: Memory read disambiguated by clang but not by gcc
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

struct a {int a, b,c,d,e,g;};
struct a ret();
int
test (int o)
{
        struct a aa,cc;
        struct a *bb = o ? &aa : &cc;
        int *p = o ? &aa.b : &cc.b;
        int *q = o ? &aa.a : &cc.a;
        *bb = ret ();
        *p = 12345;
        *q = 0;
        return *p;
}

This optimizes to 
       callq   ret@PLT
        movq    24(%rsp), %rax
        movq    %rax, 16(%rbx)
        movups  8(%rsp), %xmm0
        movups  %xmm0, (%rbx)
        movabsq $53021371269120, %rax           # imm = 0x303900000000
        movq    %rax, (%rbx)
        movl    $12345, %eax                    # imm = 0x3039
        addq    $80, %rsp

so return of 12345 is visible. While GCC can not track this

        call    ret
        movl    $12345, (%rbx)
        movl    $0, 0(%rbp)
        movl    (%rbx), %eax
        addq    $72, %rsp