[Bug middle-end/113585] New: Poor codegen turning int compare into -1,0,1

[Bug middle-end/113585] New: Poor codegen turning int compare into -1,0,1

[redbeard0531 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113585

            Bug ID: 113585
           Summary: Poor codegen turning int compare into -1,0,1
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redbeard0531 at gmail dot com
  Target Milestone: ---

https://www.godbolt.org/z/Y31xG7EeT

These two functions should be equivalent, but comp2() produces better code than
comp1() on both arm64 and x86_64

int comp1(int a, int b) {
    return a == b ? 0 : (a < b ? -1 : 1);
}

int comp2(int a, int b) {
    return a < b ? -1 : (a > b ? 1 : 0);
}

arm64:
comp1(int, int):
        cmp     w0, w1
        mov     w0, -1
        csinc   w0, w0, wzr, lt
        csel    w0, w0, wzr, ne
        ret
comp2(int, int):
        cmp     w0, w1
        cset    w0, gt
        csinv   w0, w0, wzr, ge
        ret

x86_64:
comp1(int, int):
        xor     eax, eax
        cmp     edi, esi
        je      .L1
        setge   al
        movzx   eax, al
        lea     eax, [rax-1+rax]
.L1:
        ret
comp2(int, int):
        xor     eax, eax
        cmp     edi, esi
        mov     edx, -1
        setg    al
        cmovl   eax, edx
        ret

In the arm case, I suspect that the perf will be equivalent, although comp1 has
an extra instruction, so will pay a size penalty. On x86, comp2 is branchless
while comp1 has a branch which could be problematic if not predictable. It
seems like there should be a normalization pass to convert these functions (and
other equivalent ones) into a single normalized representation so that they get
the same codegen.


PS: I tried another equivalent function and it produces even worse codegen on
x86_64, comparing the same registers twice:

int comp3(int a, int b) {
    return a > b ? 1 : (a == b ? 0 : -1);
}

comp3(int, int):
        xor     eax, eax
        cmp     edi, esi
        mov     edx, 1
        setne   al
        neg     eax
        cmp     edi, esi
        cmovg   eax, edx
        ret

[Bug middle-end/113585] Poor codegen turning int compare into -1,0,1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113585

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 59429.

*** This bug has been marked as a duplicate of bug 59429 ***