[LLVMbugs] [Bug 22723] New: Using bitwise-or versus logical-or on boolean values produces different assembly at -O3

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22723

            Bug ID: 22723
           Summary: Using bitwise-or versus logical-or on boolean values
                    produces different assembly at -O3
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: rtrieu at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Compare:

  bool test(bool x, bool y) {
    return !x | !y;
  }

And:

  bool test(bool x, bool y) {
    return !x || !y;
  }

which only differ in that the first uses a bitwise-or while the second uses a
logical-or.  Since the values are bool, both functions should produce the same
result.  However, different assembly is produced when compiled with Clang at
-O3.

Bitwise function:
    .text
    .file    "bool1.cc"
    .globl    _Z4testbb
    .align    16, 0x90
    .type    _Z4testbb, at function
_Z4testbb:                              # @_Z4testbb
    .cfi_startproc
# BB#0:                                 # %entry
    movzbl    %dil, %ecx
    xorl    $1, %ecx
    movzbl    %sil, %eax
    xorl    $1, %eax
    orl    %ecx, %eax
                                        # kill: AL<def> AL<kill> EAX<kill>
    retq
.Ltmp0:
    .size    _Z4testbb, .Ltmp0-_Z4testbb
    .cfi_endproc


    .ident    "clang version 3.7.0 (trunk 230662)"
    .section    ".note.GNU-stack","", at progbits

Logical function:
    .text
    .file    "bool2.cc"
    .globl    _Z4testbb
    .align    16, 0x90
    .type    _Z4testbb, at function
_Z4testbb:                              # @_Z4testbb
    .cfi_startproc
# BB#0:                                 # %entry
    andb    %sil, %dil
    xorb    $1, %dil
    movb    %dil, %al
    retq
.Ltmp0:
    .size    _Z4testbb, .Ltmp0-_Z4testbb
    .cfi_endproc


    .ident    "clang version 3.7.0 (trunk 230662)"
    .section    ".note.GNU-stack","", at progbits

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