This patch addresses the problem of poor code generation for the zext

v8i8 -> v8i32 on AVX machines. The codegen often scalarizes ANY_EXTEND nodes.
The DAGCombiner has two optimizations that can mitigate the problem. First,
if all of the operands of a BUILD_VECTOR node are extracted from an ZEXT/ANYEXT
nodes, then it is possible to create a new simplified BUILD_VECTOR which uses
UNDEFS/ZERO values to eliminate the scalar ZEXT/ANYEXT nodes.
Second, another dag combine optimization lowers BUILD_VECTOR into a shuffle
vector instruction.

In the case of zext v8i8->v8i32 on AVX, a value in an XMM register is to be
shuffled into a wide YMM register.

This patch modifes the second optimization and allows the creation of
shuffle vectors even when the newly generated vector and the original vector
from which we extract the values are of different types.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150340 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 14 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index d029906fc3..9fa5572e81 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7253,7 +7253,7 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   // same source type and all of the inputs must be any or zero extend.
   // Scalar sizes must be a power of two.
   EVT OutScalarTy = N->getValueType(0).getScalarType();
-  bool validTypes = SourceType != MVT::Other &&
+  bool ValidTypes = SourceType != MVT::Other &&
                  isPowerOf2_32(OutScalarTy.getSizeInBits()) &&
                  isPowerOf2_32(SourceType.getSizeInBits());
 
@@ -7263,7 +7263,8 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   // will be type-legalized to complex code sequences.
   // We perform this optimization only before the operation legalizer because we
   // may introduce illegal operations.
-  if (LegalTypes && !LegalOperations && validTypes) {
+  if ((Level == AfterLegalizeVectorOps || Level == AfterLegalizeTypes) &&
+      ValidTypes) {
     bool isLE = TLI.isLittleEndian();
     unsigned ElemRatio = OutScalarTy.getSizeInBits()/SourceType.getSizeInBits();
     assert(ElemRatio > 1 && "Invalid element size ratio");
@@ -7322,15 +7323,8 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
       break;
     }
 
-    // If the input vector type disagrees with the result of the build_vector,
-    // we can't make a shuffle.
+    // We allow up to two distinct input vectors.
     SDValue ExtractedFromVec = N->getOperand(i).getOperand(0);
-    if (ExtractedFromVec.getValueType() != VT) {
-      VecIn1 = VecIn2 = SDValue(0, 0);
-      break;
-    }
-
-    // Otherwise, remember this.  We allow up to two distinct input vectors.
     if (ExtractedFromVec == VecIn1 || ExtractedFromVec == VecIn2)
       continue;
 
@@ -7345,7 +7339,7 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
     }
   }
 
-  // If everything is good, we can make a shuffle operation.
+    // If everything is good, we can make a shuffle operation.
   if (VecIn1.getNode()) {
     SmallVector<int, 8> Mask;
     for (unsigned i = 0; i != NumInScalars; ++i) {
@@ -7371,14 +7365,35 @@ SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
       Mask.push_back(Idx+NumInScalars);
     }
 
-    // Add count and size info.
-    if (!isTypeLegal(VT))
+    // We can't generate a shuffle node with mismatched input and output types.
+    // Attempt to transform a single input vector to the correct type.
+    if ((VT != VecIn1.getValueType())) {
+      // We don't support shuffeling between TWO values of different types.
+      if (VecIn2.getNode() != 0)
+        return SDValue();
+
+      // We only support widening of vectors which are half the size of the
+      // output registers. For example XMM->YMM widening on X86 with AVX.
+      if (VecIn1.getValueType().getSizeInBits()*2 != VT.getSizeInBits())
+        return SDValue();
+
+      // Widen the input vector by adding undef values.
+      VecIn1 = DAG.getNode(ISD::CONCAT_VECTORS, N->getDebugLoc(), VT,
+                           VecIn1, DAG.getUNDEF(VecIn1.getValueType()));
+    }
+
+    // If VecIn2 is unused then change it to undef.
+    VecIn2 = VecIn2.getNode() ? VecIn2 : DAG.getUNDEF(VT);
+
+    // Only type-legal BUILD_VECTOR nodes are converted to shuffle nodes.
+    if (!isTypeLegal(VT) || !isTypeLegal(VecIn1.getValueType()) ||
+        !isTypeLegal(VecIn2.getValueType()))
       return SDValue();
 
     // Return the new VECTOR_SHUFFLE node.
     SDValue Ops[2];
     Ops[0] = VecIn1;
-    Ops[1] = VecIn2.getNode() ? VecIn2 : DAG.getUNDEF(VT);
+    Ops[1] = VecIn2;
     return DAG.getVectorShuffle(VT, N->getDebugLoc(), Ops[0], Ops[1], &Mask[0]);
   }