[LLVMbugs] [Bug 18344] New: llc doesn't optimize load from XMM well enough.

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Dec 30 04:37:08 PST 2013


            Bug ID: 18344
           Summary: llc doesn't optimize load from XMM well enough.
           Product: tools
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: llc
          Assignee: unassignedbugs at nondot.org
          Reporter: ili.filippov at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 11798
  --> http://llvm.org/bugs/attachment.cgi?id=11798&action=edit

This issue is reproducible with LLVM trunk.

The reproducer is attached.
Command to reproduce: llc -O2 reproducer.ll

llc generates the sequence of instructions:
        vmovdqa %xmm0, -24(%rsp)
        movslq  -24(%rsp), %rax
        movslq  -20(%rsp), %rcx
        movslq  -16(%rsp), %rdx
        movslq  -12(%rsp), %r8
but it seems that another sequence of instructions will be more efficient:
        vpextrd $0, %xmm0, %rax
        vpextrd $1, %xmm0, %rcx
        vpextrd $2, %xmm0, %rdx
        vpextrd $3, %xmm0, %r8

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