[Bug tree-optimization/84512] New: Missed optimization: should be precalculated in compile-time

["zamazan4ik at tut dot by" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84512

            Bug ID: 84512
           Summary: Missed optimization: should be precalculated in
                    compile-time
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zamazan4ik at tut dot by
  Target Milestone: ---

gcc(trunk) with '-O3' option for this code:


int foo()
{
    int a[10];
    for(int i = 0; i < 10; ++i)
    {
        a[i] = i*i;
    }
    int res = 0;
    for(int i = 0; i < 10; ++i)
    {
        res += a[i];
    }
    return res;
}


produces this:


foo():
  movabs rax, 4294967296
  mov QWORD PTR [rsp-56], rax
  movabs rax, 38654705668
  mov QWORD PTR [rsp-48], rax
  movabs rax, 107374182416
  mov QWORD PTR [rsp-40], rax
  movabs rax, 210453397540
  mov QWORD PTR [rsp-32], rax
  movdqa xmm0, XMMWORD PTR [rsp-40]
  paddd xmm0, XMMWORD PTR [rsp-56]
  movdqa xmm1, xmm0
  psrldq xmm1, 8
  paddd xmm0, xmm1
  movdqa xmm1, xmm0
  psrldq xmm1, 4
  paddd xmm0, xmm1
  movd eax, xmm0
  add eax, 145
  ret


but clang(trunk) with '-O3' produces this one:


foo(): # @foo()
  mov eax, 285
  ret