[llvm-bugs] [Bug 49389] New: Condition not constant folded

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=49389

            Bug ID: 49389
           Summary: Condition not constant folded
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: jmuizelaar at mozilla.com
                CC: llvm-bugs at lists.llvm.org

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>

#define N 1234

bool eat_digits(uint8_t s[N]) {
    size_t i = 0;
    while (i < N) {
        uint8_t c = s[i];
        if ('0' <= c && c <= '9') {
            i += 1;
        } else {
            break;
        }
    }
    return i <= N;
}

compiles to:

eat_digits:                             # @eat_digits
        xor     ecx, ecx
.LBB0_1:                                # =>This Inner Loop Header: Depth=1
        mov     rax, rcx
        cmp     rcx, 1234
        je      .LBB0_3
        movzx   edx, byte ptr [rdi + rax]
        add     dl, -48
        lea     rcx, [rax + 1]
        cmp     dl, 10
        jb      .LBB0_1
.LBB0_3:
        cmp     rax, 1235
        setb    al
        ret

GCC is able to compile it to:

eat_digits:
        mov     eax, 1
        ret

Adding -mllvm -enable-constraint-elimination doesn't help.

This is originally from: https://github.com/rust-lang/rust/issues/81432

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20210302/937e11c7/attachment-0001.html>