This is interesting, at least from a historical perspective. I can reproduce the problem with VC 2008 (15.00.30729.01) and VC 2010 (16.00.40219.01) (targeting either 32-bit x86 or 64-bit x64). The problem doesn't occur with any of the compilers I have tried starting with VC 2012 (17.00.61030).

The command I used to compile: cl /Ox vc15-bug.cpp /FAsc

Since VC 2008 (and 2010) is rather old and the fix has been in for several years now, I don't think you can expect any action from Microsoft except to use a newer compiler (though maybe someone can suggest a workaround).

The problem is that the test to determine if the value should be forced to 255 is done based on the loop count rather than the actual result of the i * 16 expression. And the compiler simply gets the count wrong for when it should start forcing the value to 255 . I have no idea why that happens - it's just the effect that I see:

; 6 : for( int i = 0; i < 17; i++ ) 00001 33 f6 xor esi, esi $LL4@main: 00003 8b c6 mov eax, esi 00005 c1 e0 04 shl eax, 4 ; 7 : { ; 8 : int result = i * 16; ; 9 : ; 10 : if( result > 255 ) // the value `esi` is compared with in the following line should be 15! 00008 83 fe 0e cmp esi, 14 ; 0000000eH 0000b 7e 05 jle SHORT $LN1@main ; 11 : { ; 12 : result = 255; 0000d b8 ff 00 00 00 mov eax, 255 ; 000000ffH $LN1@main: ; 13 : }

Update: All versions of VC I have installed earlier than VC 2008 have the same bug, except VC6 - compiling the program crashes the VC6 compiler:

vc15-bug.cpp(10) : fatal error C1001: INTERNAL COMPILER ERROR

So this is a bug that lasted in MSVC in one form or another for more than 10 years!