[Bug tree-optimization/115275] New: [14/15 Regression] Missed optimization for Dead Code Elimination

[652023330028 at smail dot nju.edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115275

            Bug ID: 115275
           Summary: [14/15 Regression] Missed optimization for Dead Code
                    Elimination
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 652023330028 at smail dot nju.edu.cn
  Target Milestone: ---

Hello, we noticed that the code below can be optimized by Dead Code
Elimination, but gcc -O3 missed it.

This is a regression from GCC-14.1.

https://godbolt.org/z/nc1417ed9

#include<algorithm>
unsigned short m, a, b;
void fn(unsigned short f) {
    if(
    (std::min(std::max(f, a) ? f : 0U, 84991U))
    -
    (std::min(std::max(f, b) ? f : 0U, 84991U))
    )
    {m=1;}
}

GCC -O3:
fn(unsigned short):
        movzx   eax, WORD PTR a[rip]
        movzx   ecx, WORD PTR b[rip]
        mov     edx, edi
        cmp     di, ax
        cmovnb  eax, edx
        cmp     di, cx
        cmovnb  ecx, edx
        test    ax, ax
        je      .L2
        test    cx, cx
        je      .L9
.L1:
        ret
.L2:
        test    cx, cx
        je      .L1
        cmp     dx, ax
        je      .L1
.L10:
        mov     eax, 1
        mov     WORD PTR m[rip], ax
        ret
.L9:
        mov     eax, edi
        xor     edx, edx
        cmp     dx, ax
        jne     .L10
        ret

Expected code (GCC-13.2)
fn(unsigned short):
        ret

Thank you very much for your time and effort! We look forward to hearing from
you.