[LLVMbugs] [Bug 22390] New: New vector shuffle legality: turns blendps into shufps x2.

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Jan 29 11:39:36 PST 2015


            Bug ID: 22390
           Summary: New vector shuffle legality: turns blendps into shufps
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: ahmed.bougacha at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13764
  --> http://llvm.org/bugs/attachment.cgi?id=13764&action=edit
IR testcase

For the attached IR, we used to generate:

    vpermilps    $147, %xmm0, %xmm0 ## xmm0 = xmm0[3,0,1,2]
    vblendps    $1, %xmm1, %xmm0, %xmm1 ## xmm1 = xmm1[0],xmm0[1,2,3]
    vaddps    %xmm1, %xmm0, %xmm0

With the new all-shuffles-are-legal lowering, we now generate:

    vpermilps    $147, %xmm0, %xmm2 ## xmm2 = xmm0[3,0,1,2]
    vshufps    $0, %xmm0, %xmm1, %xmm1 ## xmm1 = xmm1[0,0],xmm0[0,0]
    vshufps    $152, %xmm0, %xmm1, %xmm0 ## xmm0 = xmm1[0,2],xmm0[1,2]
    vaddps    %xmm0, %xmm2, %xmm0

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