[llvm] r251357 - reorganize logic; NFCI (retry r251349)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Mon Oct 26 16:54:14 2015
New Revision: 251357

URL: http://llvm.org/viewvc/llvm-project?rev=251357&view=rev
Log:
reorganize logic; NFCI (retry r251349)

This is a preliminary step before adding another optimization
to PerformBITCASTCombine().

..and I really hope it's NFC this time!

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=251357&r1=251356&r2=251357&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Mon Oct 26 16:54:14 2015
@@ -23123,21 +23123,21 @@ static SDValue XFormVExtractWithShuffleI
                      EltNo);
 }
 
-/// \brief Detect bitcasts between i32 to x86mmx low word. Since MMX types are
-/// special and don't usually play with other vector types, it's better to
-/// handle them early to be sure we emit efficient code by avoiding
-/// store-load conversions.
 static SDValue PerformBITCASTCombine(SDNode *N, SelectionDAG &DAG) {
-  if (N->getValueType(0) != MVT::x86mmx ||
-      N->getOperand(0)->getOpcode() != ISD::BUILD_VECTOR ||
-      N->getOperand(0)->getValueType(0) != MVT::v2i32)
-    return SDValue();
+  SDValue N0 = N->getOperand(0);
+  EVT VT = N->getValueType(0);
 
-  SDValue V = N->getOperand(0);
-  ConstantSDNode *C = dyn_cast<ConstantSDNode>(V.getOperand(1));
-  if (C && C->getZExtValue() == 0 && V.getOperand(0).getValueType() == MVT::i32)
-    return DAG.getNode(X86ISD::MMX_MOVW2D, SDLoc(V.getOperand(0)),
-                       N->getValueType(0), V.getOperand(0));
+  // Detect bitcasts between i32 to x86mmx low word. Since MMX types are
+  // special and don't usually play with other vector types, it's better to
+  // handle them early to be sure we emit efficient code by avoiding
+  // store-load conversions.
+  if (VT == MVT::x86mmx && N0.getOpcode() == ISD::BUILD_VECTOR &&
+      N0.getValueType() == MVT::v2i32 &&
+      isa<ConstantSDNode>(N0.getOperand(1))) {
+    SDValue N00 = N0->getOperand(0);
+    if (N0.getConstantOperandVal(1) == 0 && N00.getValueType() == MVT::i32)
+      return DAG.getNode(X86ISD::MMX_MOVW2D, SDLoc(N00), VT, N00);
+  }
 
   return SDValue();
 }