[llvm-bugs] [Bug 42308] New: Propagate constants into loads if dominated by str(n)cmp/memcmp

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42308

            Bug ID: 42308
           Summary: Propagate constants into loads if dominated by
                    str(n)cmp/memcmp
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

Motivation:

char f(char* s) {
  if (strcmp(s, "test") == 0) return s[0];
  return '-';
}

--->

char f2(char* s) {
  if (strcmp(s, "test") == 0) return 't';
  return '-';
}

f(char*):                                 # @f(char*)
        push    rbx
        mov     rbx, rdi
        mov     esi, offset .L.str
        call    strcmp
        mov     ecx, eax
        mov     al, 45
        test    ecx, ecx
        je      .LBB0_1
        pop     rbx
        ret
.LBB0_1:
        mov     al, byte ptr [rbx]
        pop     rbx
        ret
f2(char*):                                # @f2(char*)
        push    rax
        mov     esi, offset .L.str
        call    strcmp
        test    eax, eax
        mov     ecx, 116
        mov     eax, 45
        cmove   eax, ecx
        pop     rcx
        ret
.L.str:
        .asciz  "test"

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