[LLVMbugs] [Bug 1721] New: Incorrect evaluation of expression containing bitfield items

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue Oct 2 09:37:38 PDT 2007


           Summary: Incorrect evaluation of expression containing bitfield
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: richard.smith at antixlabs.com
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=1150)
 --> (http://llvm.org/bugs/attachment.cgi?id=1150)
Test case

(Tested with LLVM 2.1 with gcc 4.0)

The attached demo has a 33 bit integer, with value 1<<32. The result of (item +
item) should be zero because the value overflows, but the test fails at all
optimisation levels.

>From looking at the llvm disassembly it appears the result of the addition is
not ANDed with 0x1FFFFFFFF as would be expected.

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