[LLVMbugs] [Bug 10171] New: Substitute unpckhpd, unpcklpd and movddup for shufpd

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Wed Jun 22 11:10:49 PDT 2011


           Summary: Substitute unpckhpd, unpcklpd and movddup for shufpd
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: jmuizelaar at mozilla.com
                CC: llvmbugs at cs.uiuc.edu

shufpd    $0, %xmm0, %xmm0 ## xmm0 = xmm0[0,0]
can be replaced with unpcklpd when restricted to sse2 and movddup when using

shufpd    $3, %xmm0, %xmm0 ## xmm0 = xmm0[1,1]
can be replaced with unpckhpd

These variants are faster on some processors and take a byte less to encode.
moddup also allows the source to be different than the destination which can
allow a copy to be avoided.

GCC also makes these substitutions.

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