[llvm-bugs] [Bug 33691] New: Recognise vector rotations with non-splat constants

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Jul 5 03:53:13 PDT 2017


            Bug ID: 33691
           Summary: Recognise vector rotations with non-splat constants
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: Andrew.Zhogin at gmail.com, elena.demikhovsky at intel.com,
                    llvm-bugs at lists.llvm.org, zvi.rackover at intel.com

We fail to recognise or(lshr(x,c1),shl(x,c1)) style patterns for vectors where
the constant values are not splats:

define <4 x i32> @rot_v4i32(<4 x i32> %x) {
  %1 = lshr <4 x i32> %x, <i32 1, i32 2, i32 3, i32 4>
  %2 = shl <4 x i32> %x, <i32 31, i32 30, i32 29, i32 28>
  %3 = or <4 x i32> %1, %2
  ret <4 x i32> %3

llc -mcpu=bdver4
  vpshld {{.*}}(%rip), %xmm0, %xmm1
  vpshld {{.*}}(%rip), %xmm0, %xmm0
  vpor %xmm0, %xmm1, %xmm0

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