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Date: Fri, 26 May 2006 17:52:30 +0000 (GMT+00:00)
From: "Martin Sebor (JIRA)" <jira@apache.org>
To: stdcxx-dev@incubator.apache.org
Subject: [jira] Created: (STDCXX-190) [MSVC] bogus performance warning
 C4800: forcing value to bool
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[MSVC] bogus performance warning C4800: forcing value to bool
-------------------------------------------------------------

         Key: STDCXX-190
         URL: http://issues.apache.org/jira/browse/STDCXX-190
     Project: C++ Standard Library
        Type: Bug

  Components: External  
    Versions: 4.1.3    
 Environment: MSVC all versions up to and including 8.0
    Reporter: Martin Sebor
    Priority: Trivial


Copied from http://lab.msdn.microsoft.com/productfeedback/viewfeedback.aspx?feedbackid=96a52a80-a701-4402-864a-abd03917538c:

Bug ID:  	FDBK50482
Problem Type: 	Bug
Status: 	New
Microsoft Status:   	Not Reviewed
Opened Date: 	2006-05-26 10:42:12
Opened By: 	Martin Sebor
	
Product/Technology: 	Visual C++
Version: 	Visual Studio 2005
Product Language: 	English
Category: 	Language/Compiler
OS: 	Windows 2000 Server
OS Language: 	US English
Submission Language: 	English
Description: 	
Opened by Martin Sebor on 2006-05-26 at 10:42:12
    	
The warnings in the program below are bogus since the generated code is identical in all three cases.

Steps to Reproduce: 	$ cat -n t.cpp && cl -c -W3 -O2 -nologo -Fa t.cpp
1 bool f1 (int i)
2 {
3 return i & 2;
4 }
5
6 bool f2 (int i)
7 {
8 const bool b = i & 2;
9 return b;
10 }
11
12 bool f3 (int i)
13 {
14 const bool b = 0 != (i & 2);
15 return b;
16 }
t.cpp
t.cpp(3) : warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning)
t.cpp(8) : warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning)
Actual Results: 	$ cat t.asm
; Listing generated by Microsoft (R) Optimizing Compiler Version 14.00.50727.42

TITLE C:\contrib\cygwin\tmp\t.cpp
.686P
.XMM
include listing.inc
.model flat

INCLUDELIB LIBCMT
INCLUDELIB OLDNAMES

PUBLIC ?f1@@YA_NH@Z ; f1
; Function compile flags: /Ogtpy
; COMDAT ?f1@@YA_NH@Z
_TEXT SEGMENT
_i$ = 8 ; size = 4
?f1@@YA_NH@Z PROC ; f1, COMDAT
; File c:\contrib\cygwin\tmp\t.cpp
; Line 3
mov eax, DWORD PTR _i$[esp-4]
shr eax, 1
and al, 1
; Line 4
ret 0
?f1@@YA_NH@Z ENDP ; f1
_TEXT ENDS
PUBLIC ?f2@@YA_NH@Z ; f2
; Function compile flags: /Ogtpy
; COMDAT ?f2@@YA_NH@Z
_TEXT SEGMENT
_i$ = 8 ; size = 4
?f2@@YA_NH@Z PROC ; f2, COMDAT
; Line 8
mov eax, DWORD PTR _i$[esp-4]
shr eax, 1
and al, 1
; Line 10
ret 0
?f2@@YA_NH@Z ENDP ; f2
_TEXT ENDS
PUBLIC ?f3@@YA_NH@Z ; f3
; Function compile flags: /Ogtpy
; COMDAT ?f3@@YA_NH@Z
_TEXT SEGMENT
_i$ = 8 ; size = 4
?f3@@YA_NH@Z PROC ; f3, COMDAT
; Line 14
mov eax, DWORD PTR _i$[esp-4]
shr eax, 1
and al, 1
; Line 16
ret 0
?f3@@YA_NH@Z ENDP ; f3
_TEXT ENDS
END
Expected Results: 	No warnings.

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