[LLVMbugs] [Bug 21876] New: [AVX2] Cannot select: v8i32 = X86ISD::VZEXT with old vector shuffle lowering

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21876

            Bug ID: 21876
           Summary: [AVX2] Cannot select: v8i32 = X86ISD::VZEXT with old
                    vector shuffle lowering
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: qcolombet at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13515
  --> http://llvm.org/bugs/attachment.cgi?id=13515&action=edit
IR to reproduce the problem.

While trying to compare the performance of the old vector shuffle lowering
against the new one, I ran into this cannot select error.
This used to work until fairly recently, I think, r223304, but it is now broken
with r223979.

To reproduce:
llc -mtriple=x86_64-apple-macosx
-x86-experimental-vector-shuffle-lowering=false  -mattr=+avx2 tmp3.ll

Removing avx2 or using the new vector shuffle lowering works.

Until the old vector shuffle lowering is official dead, we should fix that to
ease comparison.

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