Don't insert 128-bit UNDEF into 256-bit vectors. Just keep the 256-bit vector. Original patch by Elena Demikhovsky. Tweaked by me to allow possibility of covering more cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158792 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 15 insertions, 4 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index dec8d07d99..2576821d39 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -99,6 +99,10 @@ static SDValue Extract128BitVector(SDValue Vec, unsigned IdxVal,
 static SDValue Insert128BitVector(SDValue Result, SDValue Vec,
                                   unsigned IdxVal, SelectionDAG &DAG,
                                   DebugLoc dl) {
+  // Inserting UNDEF is Result
+  if (Vec.getOpcode() == ISD::UNDEF)
+    return Result;
+
   EVT VT = Vec.getValueType();
   assert(VT.getSizeInBits() == 128 && "Unexpected vector size!");
 
@@ -114,9 +118,8 @@ static SDValue Insert128BitVector(SDValue Result, SDValue Vec,
                                * ElemsPerChunk);
 
   SDValue VecIdx = DAG.getConstant(NormalizedIdxVal, MVT::i32);
-  Result = DAG.getNode(ISD::INSERT_SUBVECTOR, dl, ResultVT, Result, Vec,
-                       VecIdx);
-  return Result;
+  return DAG.getNode(ISD::INSERT_SUBVECTOR, dl, ResultVT, Result, Vec,
+                     VecIdx);
 }
 
 /// Concat two 128-bit vectors into a 256 bit vector using VINSERTF128
diff --git a/test/CodeGen/X86/avx-shuffle-x86_32.ll b/test/CodeGen/X86/avx-shuffle-x86_32.ll
index 5268ec3a56..e203c4ed02 100755
--- a/test/CodeGen/X86/avx-shuffle-x86_32.ll
+++ b/test/CodeGen/X86/avx-shuffle-x86_32.ll
@@ -4,5 +4,5 @@ define <4 x i64> @test1(<4 x i64> %a) nounwind {
  %b = shufflevector <4 x i64> %a, <4 x i64> undef, <4 x i32> <i32 1, i32 3, i32 5, i32 7>
  ret <4 x i64>%b
  ; CHECK: test1:
- ; CHECK: vinsertf128
+ ; CHECK-NOT: vinsertf128
  }
diff --git a/test/CodeGen/X86/avx-shuffle.ll b/test/CodeGen/X86/avx-shuffle.ll
index f1debffd11..edfe4ab6c7 100644
--- a/test/CodeGen/X86/avx-shuffle.ll
+++ b/test/CodeGen/X86/avx-shuffle.ll
@@ -219,3 +219,11 @@ define <16 x i16> @narrow(<16 x i16> %a) nounwind alwaysinline {
   %t = shufflevector <16 x i16> %a, <16 x i16> undef, <16 x i32> <i32 2, i32 3, i32 undef, i32 1, i32 6, i32 7, i32 4, i32 5, i32 10, i32 11, i32 8, i32 undef, i32 14, i32 15, i32 undef, i32 undef>
   ret <16 x i16> %t
 }
+
+;CHECK: test17
+;CHECK-NOT: vinsertf128
+;CHECK: ret
+define   <8 x float> @test17(<4 x float> %y) {
+  %x = shufflevector <4 x float> %y, <4 x float> undef, <8 x i32> <i32 undef, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
+  ret <8 x float> %x
+}