[LLVMbugs] [Bug 11946] New: Poor optimization of llvm.memcpy of structs with padding

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11946

             Bug #: 11946
           Summary: Poor optimization of llvm.memcpy of structs with
                    padding
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: clattner at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The optimizer and code generator do nasty things to structs that have padding
in them.  We should fix this by having the frontend generate a small bit of
metadata on struct copies to indicate which fields are undefined.

A sketch of how this can work along with some motivation is here:
http://nondot.org/sabre/LLVMNotes/BetterStructureCopyOptimization.txt

-Chris

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