[LLVMbugs] [Bug 23705] New: Different result (integer wrap) by optimization setting

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Sat May 30 00:52:33 PDT 2015


            Bug ID: 23705
           Summary: Different result (integer wrap) by optimization
           Product: tools
           Version: 3.5
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: llvm-gcc
          Assignee: unassignedbugs at nondot.org
          Reporter: HHG01200 at nifty.ne.jp
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

On Mac OS X 10.10.3, Apple LLVM 6.0, with no optimization (-O0) or -O1, print
"A" (expected result).
However, with optimization (-Os), print "B" (not expected result).

file 1
#include    <stdio.h>

extern    int    GetA();
extern    int    GetB();
extern    int    GetC();

int    main()
    int    a = GetA();
    int    c = GetC();
    int    d = GetB() - c;

    if ((a - c) < (d))
    return 0;

file 2
#include    <limits.h>

int    GetA()
    return INT_MAX;

int    GetB()
    return INT_MIN;

int    GetC()
    return INT_MAX / 2;

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