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copied!<blockquote> <p>EDIT: Saw OP's assembly listing for my code. I doubt this is even a <em>general bug with VS2011</em> now. This may simply be a special case bug for OP's code. I ran OP's code as-is with clang 3.2, gcc 4.6.2 and VS2010 and in all cases the <em>max differences</em> were at ~1%.</p> </blockquote> <p>Just compiled the sources with suitable modifications to my <code>ne.c</code> file and the <code>/O2</code> and <code>/GL</code> flags. Here's the source </p> <pre><code>int ne1(int n) { return n != 0; } int ne2(int n) { return n < 0 || n > 0; } int ne3(int n) { return !(n == 0); } int main() { int p = ne1(rand()), q = ne2(rand()), r = ne3(rand());} </code></pre> <p>and the corresponding assembly:</p> <pre><code> ; Listing generated by Microsoft (R) Optimizing Compiler Version 16.00.30319.01 TITLE D:\llvm_workspace\tests\ne.c .686P .XMM include listing.inc .model flat INCLUDELIB OLDNAMES EXTRN @__security_check_cookie@4:PROC EXTRN _rand:PROC PUBLIC _ne3 ; Function compile flags: /Ogtpy ; COMDAT _ne3 _TEXT SEGMENT _n$ = 8 ; size = 4 _ne3 PROC ; COMDAT ; File d:\llvm_workspace\tests\ne.c ; Line 11 xor eax, eax cmp DWORD PTR _n$[esp-4], eax setne al ; Line 12 ret 0 _ne3 ENDP _TEXT ENDS PUBLIC _ne2 ; Function compile flags: /Ogtpy ; COMDAT _ne2 _TEXT SEGMENT _n$ = 8 ; size = 4 _ne2 PROC ; COMDAT ; Line 7 xor eax, eax cmp eax, DWORD PTR _n$[esp-4] sbb eax, eax neg eax ; Line 8 ret 0 _ne2 ENDP _TEXT ENDS PUBLIC _ne1 ; Function compile flags: /Ogtpy ; COMDAT _ne1 _TEXT SEGMENT _n$ = 8 ; size = 4 _ne1 PROC ; COMDAT ; Line 3 xor eax, eax cmp DWORD PTR _n$[esp-4], eax setne al ; Line 4 ret 0 _ne1 ENDP _TEXT ENDS PUBLIC _main ; Function compile flags: /Ogtpy ; COMDAT _main _TEXT SEGMENT _main PROC ; COMDAT ; Line 14 call _rand call _rand call _rand xor eax, eax ret 0 _main ENDP _TEXT ENDS END </code></pre> <p><code>ne2()</code> which used the <code><</code>, <code>></code> and <code>||</code> operators is <strong>clearly</strong> more expensive. <code>ne1()</code> and <code>ne3()</code> which use the <code>==</code> and <code>!=</code> operators respectively, are terser and equivalent.</p> <p>Visual Studio 2011 is <em>in beta</em>. I would consider this as a bug. My tests with two other compilers namely <em>gcc 4.6.2</em> and <em>clang 3.2</em>, with the <code>O2</code> optimization switch yielded the exact same assembly for all three tests (that I had) on my Windows 7 box. Here's a summary:</p> <pre><code>$ cat ne.c #include <stdbool.h> bool ne1(int n) { return n != 0; } bool ne2(int n) { return n < 0 || n > 0; } bool ne3(int n) { return !(n != 0); } int main() {} </code></pre> <p>yields with gcc:</p> <pre><code>_ne1: LFB0: .cfi_startproc movl 4(%esp), %eax testl %eax, %eax setne %al ret .cfi_endproc LFE0: .p2align 2,,3 .globl _ne2 .def _ne2; .scl 2; .type 32; .endef _ne2: LFB1: .cfi_startproc movl 4(%esp), %edx testl %edx, %edx setne %al ret .cfi_endproc LFE1: .p2align 2,,3 .globl _ne3 .def _ne3; .scl 2; .type 32; .endef _ne3: LFB2: .cfi_startproc movl 4(%esp), %ecx testl %ecx, %ecx sete %al ret .cfi_endproc LFE2: .def ___main; .scl 2; .type 32; .endef .section .text.startup,"x" .p2align 2,,3 .globl _main .def _main; .scl 2; .type 32; .endef _main: LFB3: .cfi_startproc pushl %ebp .cfi_def_cfa_offset 8 .cfi_offset 5, -8 movl %esp, %ebp .cfi_def_cfa_register 5 andl $-16, %esp call ___main xorl %eax, %eax leave .cfi_restore 5 .cfi_def_cfa 4, 4 ret .cfi_endproc LFE3: </code></pre> <p>and with clang: </p> <pre><code> .def _ne1; .scl 2; .type 32; .endef .text .globl _ne1 .align 16, 0x90 _ne1: cmpl $0, 4(%esp) setne %al movzbl %al, %eax ret .def _ne2; .scl 2; .type 32; .endef .globl _ne2 .align 16, 0x90 _ne2: cmpl $0, 4(%esp) setne %al movzbl %al, %eax ret .def _ne3; .scl 2; .type 32; .endef .globl _ne3 .align 16, 0x90 _ne3: cmpl $0, 4(%esp) sete %al movzbl %al, %eax ret .def _main; .scl 2; .type 32; .endef .globl _main .align 16, 0x90 _main: pushl %ebp movl %esp, %ebp calll ___main xorl %eax, %eax popl %ebp ret </code></pre> <p><strong><em>My suggestion would be to file this as a bug with <a href="http://connect.microsoft.com/visualstudio" rel="noreferrer">Microsoft Connect</a>.</em></strong></p> <p>Note: I compiled them as C source since I don't think using the corresponding C++ compiler would make any significant change here.</p>

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