[llvm-bugs] [Bug 40080] New: [LoopVectorizer] crash with -force-vector-width=2

via llvm-bugs llvm-bugs at lists.llvm.org
Tue Dec 18 05:47:28 PST 2018


            Bug ID: 40080
           Summary: [LoopVectorizer]  crash with -force-vector-width=2
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: paulsson at linux.vnet.ibm.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 21245
  --> https://bugs.llvm.org/attachment.cgi?id=21245&action=edit
reduced testcase

This test case contains a loop with a load that gets a disabling (300000) cost,
so normally this would not get vectorized.

Still, if vectorization is forced bad code is generated, which should probably
be investigated:

opt -mtriple=s390x-unknown-linux -mcpu=z13 -o out.opt.ll tc_LV_width2.ll  -O3
-S -force-vector-width=2 -unroll-count=1

Instruction does not dominate all uses!
  %17 = phi <2 x double> [ %10, %pred.load.continue ], [ %16, %pred.load.if3 ]
  %2 = shufflevector <2 x double> %vector.recur, <2 x double> %17, <2 x i32>
<i32 1, i32 2>

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