[llvm-bugs] [Bug 50537] New: Use xorl instead of xorq when possible

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50537

            Bug ID: 50537
           Summary: Use xorl instead of xorq when possible
           Product: new-bugs
           Version: 12.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: josephcsible at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Consider this C code:

unsigned long f(unsigned long x) {
    return ((x & 1) + (x >> 1)) * (((x & 1) ^ 1) + x);
}

With -Oz, Clang produces this:

f:                                      # @f
        movl    %edi, %eax
        andl    $1, %eax
        movq    %rdi, %rcx
        shrq    %rcx
        addq    %rax, %rcx
        xorq    $1, %rax
        addq    %rdi, %rax
        imulq   %rcx, %rax
        retq

https://godbolt.org/z/Kqsa58Kn9

It should do "xorl    $1, %eax" instead of "xorq    $1, %rax" there, as they
both have the same effect since rax will always be either 0 or 1 there, and the
latter requires an extra 1-byte REX prefix.

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