From e855efe42407dd67f6a513927d0669cb7a66f448 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Sat, 27 Jun 2020 15:06:49 +0100
Subject: [PATCH] [X86][AVX] SimplifyDemandedVectorEltsForTargetNode - reduce
 width of X86ISD::VPERMIL2

If we don't need the elements of the upper lanes, reduce the width of the X86ISD::VPERMIL2 node.
---
 llvm/lib/Target/X86/X86ISelLowering.cpp  | 20 +++++++++++++++++++-
 llvm/test/CodeGen/X86/var-permute-256.ll |  5 +----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 2e23bcb..fd69791 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -37165,7 +37165,25 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
       SDValue Insert =
           insertSubVector(UndefVec, ExtOp, 0, TLO.DAG, DL, ExtSizeInBits);
       return TLO.CombineTo(Op, Insert);
-    } 
+    }
+    case X86ISD::VPERMIL2: {
+      SDLoc DL(Op);
+      MVT ExtVT = VT.getSimpleVT();
+      ExtVT = MVT::getVectorVT(ExtVT.getScalarType(),
+                               ExtSizeInBits / ExtVT.getScalarSizeInBits());
+      SDValue Ext0 =
+          extractSubVector(Op.getOperand(0), 0, TLO.DAG, DL, ExtSizeInBits);
+      SDValue Ext1 =
+          extractSubVector(Op.getOperand(1), 0, TLO.DAG, DL, ExtSizeInBits);
+      SDValue Ext2 =
+          extractSubVector(Op.getOperand(2), 0, TLO.DAG, DL, ExtSizeInBits);
+      SDValue ExtOp =
+          TLO.DAG.getNode(Opc, DL, ExtVT, Ext0, Ext1, Ext2, Op.getOperand(3));
+      SDValue UndefVec = TLO.DAG.getUNDEF(VT);
+      SDValue Insert =
+          insertSubVector(UndefVec, ExtOp, 0, TLO.DAG, DL, ExtSizeInBits);
+      return TLO.CombineTo(Op, Insert);
+    }
     }
   }
 
diff --git a/llvm/test/CodeGen/X86/var-permute-256.ll b/llvm/test/CodeGen/X86/var-permute-256.ll
index 6a9f47d..ff099c1 100644
--- a/llvm/test/CodeGen/X86/var-permute-256.ll
+++ b/llvm/test/CodeGen/X86/var-permute-256.ll
@@ -1104,11 +1104,8 @@ entry:
 define <4 x i32> @var_shuffle_v4i32_from_v8i32(<8 x i32> %v, <4 x i32> %indices) unnamed_addr nounwind {
 ; XOP-LABEL: var_shuffle_v4i32_from_v8i32:
 ; XOP:       # %bb.0: # %entry
-; XOP-NEXT:    # kill: def $xmm1 killed $xmm1 def $ymm1
 ; XOP-NEXT:    vperm2f128 {{.*#+}} ymm2 = ymm0[2,3,2,3]
-; XOP-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; XOP-NEXT:    vpermil2ps $0, %ymm1, %ymm2, %ymm0, %ymm0
-; XOP-NEXT:    # kill: def $xmm0 killed $xmm0 killed $ymm0
+; XOP-NEXT:    vpermil2ps $0, %xmm1, %xmm2, %xmm0, %xmm0
 ; XOP-NEXT:    vzeroupper
 ; XOP-NEXT:    retq
 ;
-- 
2.7.4