[LLVMbugs] [Bug 19711] New: ComputeMaskedBits & friends should know that multiplying by a power of two leaves low bits clear

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19711

            Bug ID: 19711
           Summary: ComputeMaskedBits & friends should know that
                    multiplying by a power of two leaves low bits clear
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: clattner at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

John Regehr reports that GCC is folding X*2&1 to zero.  ComputedMaskedBits and
SimplifyDemandedBits should know that multiplications by powers of two leave
predictable zeros in the low bits of the result.

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