[PATCH] [AArch64] Fix a build_vector pattern fail caused by defect in isBuildVectorAllZeros().

[Kevin Qin]

Sorry for following up this issue late. This patch is to normalize all constants building a vector. The value of constant nodes will be truncated to fit element width.

http://reviews.llvm.org/D4228

Files:
  lib/Target/AArch64/AArch64ISelLowering.cpp
  test/CodeGen/AArch64/arm64-build-vector.ll

Index: lib/Target/AArch64/AArch64ISelLowering.cpp
===================================================================
--- lib/Target/AArch64/AArch64ISelLowering.cpp
+++ lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -5181,11 +5181,37 @@
   return Op;
 }
 
+// Normalize the operands of BUILD_VECTOR. The value of constant operands will
+// be truncated to fit element width.
+static SDValue NormalizeBuildVector(SDValue Op,
+                                    SelectionDAG &DAG) {
+  assert(Op.getOpcode() == ISD::BUILD_VECTOR && "Unknown opcode!");
+  SDLoc dl(Op);
+  EVT VT = Op.getValueType();
+  EVT EltTy= VT.getVectorElementType();
+
+  if (EltTy.isFloatingPoint() || EltTy.getSizeInBits() > 16)
+    return Op;
+
+  SmallVector<SDValue, 16> Ops;
+  for (unsigned I = 0, E = VT.getVectorNumElements(); I != E; ++I) {
+    SDValue Lane = Op.getOperand(I);
+    if (Lane.getOpcode() == ISD::Constant) {
+      APInt LowBits(EltTy.getSizeInBits(),
+                    cast<ConstantSDNode>(Lane)->getZExtValue());
+      Lane = DAG.getConstant(LowBits.getZExtValue(), MVT::i32);
+    }
+    Ops.push_back(Lane);
+  }
+  return DAG.getNode(ISD::BUILD_VECTOR, dl, VT, Ops);
+}
+
 SDValue AArch64TargetLowering::LowerBUILD_VECTOR(SDValue Op,
                                                  SelectionDAG &DAG) const {
-  BuildVectorSDNode *BVN = cast<BuildVectorSDNode>(Op.getNode());
   SDLoc dl(Op);
   EVT VT = Op.getValueType();
+  Op = NormalizeBuildVector(Op, DAG);
+  BuildVectorSDNode *BVN = cast<BuildVectorSDNode>(Op.getNode());
 
   APInt CnstBits(VT.getSizeInBits(), 0);
   APInt UndefBits(VT.getSizeInBits(), 0);
Index: test/CodeGen/AArch64/arm64-build-vector.ll
===================================================================
--- test/CodeGen/AArch64/arm64-build-vector.ll
+++ test/CodeGen/AArch64/arm64-build-vector.ll
@@ -36,7 +36,7 @@
 
 define <8 x i16> @build_all_zero(<8 x i16> %a) #1 {
 ; CHECK-LABEL: build_all_zero:
-; CHECK: movn	w[[GREG:[0-9]+]], #0x517f
+; CHECK: movz	w[[GREG:[0-9]+]], #0xae80
 ; CHECK-NEXT:	fmov	s[[FREG:[0-9]+]], w[[GREG]]
 ; CHECK-NEXT:	mul.8h	v0, v0, v[[FREG]]
   %b = add <8 x i16> %a, <i16 -32768, i16 undef, i16 undef, i16 undef, i16 undef, i16 undef, i16 undef, i16 undef>
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