[LLVMbugs] [Bug 17963] New: SCEV dropping NSW/NUW flags on non-unit stride access

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Sat Nov 16 13:25:51 PST 2013


            Bug ID: 17963
           Summary: SCEV dropping NSW/NUW flags on non-unit stride access
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: renato.golin at linaro.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 11556
  --> http://llvm.org/bugs/attachment.cgi?id=11556&action=edit
example in C and IR

The attached C code, compiled with Clang to the attached IR has a
multiplicative factor of 2, and SCEV::getMulExpr() is losing the NSW that is on
the multiplication for being too conservative.

Keeping the NSW flags will help the non-unit stride analysis on the vectorizer.

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