[llvm-bugs] [Bug 34711] New: After r311849 Loop Vectorizer generates broken code

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Sat Sep 23 10:41:41 PDT 2017


            Bug ID: 34711
           Summary: After r311849 Loop Vectorizer generates broken code
           Product: tools
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: opt
          Assignee: unassignedbugs at nondot.org
          Reporter: Alberto.Magni at microsoft.com
                CC: ayal.zaks at intel.com, llvm-bugs at lists.llvm.org

Created attachment 19194
  --> https://bugs.llvm.org/attachment.cgi?id=19194&action=edit

The loop vectorizer breaks the two attached programs:

Instruction does not dominate all uses!
  %6 = shufflevector <2 x i16> %vector.recur, <2 x i16> %5, <2 x i32> <i32 1,
i32 2>
  %1 = sext <2 x i16> %6 to <2 x i32>

The file before_lv.ll is the one that originally triggered the problem for me.
reduced.ll has been obtained with bugpoint starting from before_lv.ll

To reproduce:
opt -force-vector-width=2 -loop-vectorize reduced.ll -S -o x.ll
opt -force-vector-width=2 -loop-vectorize before_lv.ll -S -o x.ll

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