Microsoft KB Archive/114077

{|
 * width="100%"|

FIX: Code Movement with Huge Pointer Expression in Loop

 * }

Q114077

1.00 WINDOWS kbtool kbfixlist kbbuglist -- The information in this article applies to: - The Microsoft C/C++ Compiler (CL.EXE), included with: - Microsoft Visual C++ for Windows, versions 1.0 -- SYMPTOMS ======== In certain cases when the C/C++ compiler reorganizes code for efficiency after code generation, it will do it incorrectly. The generated code will not run as expected because of this. A specific example of this problem can be reproduced by building and running the sample code below. RESOLUTION ========== To work around the problem illustrated by the sample code, do one of the following: - Disable post-code-generation optimizations for the module containing the function by compiling with the /Oo- option. This will prevent the compiler from rearranging the code that causes the problem. - Do not use the /Oe and /Ol options together when compiling the module containing the function. - Use the #pragma optimize directive to disable the /Oe or /Ol options for the function. This is indicated in the sample code below. STATUS ====== Microsoft has confirmed this to be a problem in the Microsoft products listed above. This problem was corrected in Visual C++ version 1.5. MORE INFORMATION ================ The specific problem in the sample code below is that the code generated to test that n = 1 is rearranged. This causes the test to fail when it should not, so that the while loop is exited without looping. Sample Code --- /* Compile options needed: /Oel (or /O2, or /Ox; both include /Oel) */ #include #include #define COUNT 5 int dummy_fcn { static int accum; accum++; if ( accum <= COUNT ) return 1; else return 0; } /* uncomment #pragmas to correct problem #pragma( "l", off ) */ void main { int __huge *hptr; int n = 1; hptr = _fmalloc( sizeof( int ) ); if ( hptr == NULL ) { printf( "Test failed!\n" ); exit( 1 ); } *hptr = 0; while ( n == 1 ) { /* dummy_fcn will return 1, COUNT times. The reason this is done is to force the while loop to be executed a certain number of times, by keeping n = 1. */ n = dummy_fcn; /* If the correct code is generated, the value pointed to by hptr should be incremented COUNT+1 times. Since it is initialized to 0 before the loop, its value after the loop should be COUNT+1. */ *hptr = *hptr + 1; } if ( *hptr == COUNT+1 ) printf( "Test succeeded!\n" ); else printf( "Test failed!\n" ); } /* #pragma optimize( "l", on ) */ Additional reference words: 8.00 1.00 KBCategory: kbtool kbfixlist kbbuglist KBSubcategory: CLIss

Keywords : kb16bitonly kbCompiler

Issue type :

Technology : kbVCsearch kbAudDeveloper kbCVCComp