1 files changed, 43 insertions, 6 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index c77355f9179..79e99db34bf 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -8283,7 +8283,18 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, unsigned X86CC,
 
   unsigned Opcode = 0;
   unsigned NumOperands = 0;
-  switch (Op.getNode()->getOpcode()) {
+
+  // Truncate operations may prevent the merge of the SETCC instruction
+  // and the arithmetic intruction before it. Attempt to truncate the operands
+  // of the arithmetic instruction and use a reduced bit-width instruction.
+  bool NeedTruncation = false;
+  unsigned InOpcode = Op.getNode()->getOpcode();
+  if (Op->getOpcode() == ISD::TRUNCATE && Op->hasOneUse()) {
+    NeedTruncation = true;
+    InOpcode = Op->getOperand(0)->getOpcode();
+  }
+
+  switch (InOpcode) {
   case ISD::ADD:
     // Due to an isel shortcoming, be conservative if this add is likely to be
     // selected as part of a load-modify-store instruction. When the root node
@@ -8339,7 +8350,7 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, unsigned X86CC,
 
       if (User->getOpcode() != ISD::BRCOND &&
           User->getOpcode() != ISD::SETCC &&
-          (User->getOpcode() != ISD::SELECT || UOpNo != 0)) {
+          !(User->getOpcode() == ISD::SELECT && UOpNo == 0)) {
         NonFlagUse = true;
         break;
       }
@@ -8360,11 +8371,9 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, unsigned X86CC,
         goto default_case;
 
     // Otherwise use a regular EFLAGS-setting instruction.
-    switch (Op.getNode()->getOpcode()) {
+    switch (InOpcode) {
     default: llvm_unreachable("unexpected operator!");
-    case ISD::SUB:
-      Opcode = X86ISD::SUB;
-      break;
+    case ISD::SUB: Opcode = X86ISD::SUB; break;
     case ISD::OR:  Opcode = X86ISD::OR;  break;
     case ISD::XOR: Opcode = X86ISD::XOR; break;
     case ISD::AND: Opcode = X86ISD::AND; break;
@@ -8385,6 +8394,34 @@ SDValue X86TargetLowering::EmitTest(SDValue Op, unsigned X86CC,
     break;
   }
 
+  if (NeedTruncation) {
+    SDValue WideVal = Op->getOperand(0);
+    EVT VT = Op.getValueType();
+    EVT WideVT = WideVal.getValueType();
+    unsigned ConvertedOp = 0;
+
+    // Use a target machine opcode to prevent further DAGCombine
+    // optimizations that may separate the arithmetic operations from the
+    // setcc node.
+    switch (WideVal.getOpcode()) {
+      default: break;
+      case ISD::ADD: ConvertedOp = X86ISD::ADD; break;
+      case ISD::SUB: ConvertedOp = X86ISD::SUB; break;
+      case ISD::AND: ConvertedOp = X86ISD::AND; break;
+      case ISD::OR:  ConvertedOp = X86ISD::OR;  break;
+      case ISD::XOR: ConvertedOp = X86ISD::XOR; break;
+    }
+
+    if (ConvertedOp && WideVal.hasOneUse()) {
+      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+      if (TLI.isOperationLegal(WideVal.getOpcode(), WideVT)) {
+        SDValue V0 = DAG.getNode(ISD::TRUNCATE, dl, VT, WideVal.getOperand(0));
+        SDValue V1 = DAG.getNode(ISD::TRUNCATE, dl, VT, WideVal.getOperand(1));
+        Op = DAG.getNode(ConvertedOp, dl, VT, V0, V1);
+      }
+    }
+  }
+
   if (Opcode == 0)
     // Emit a CMP with 0, which is the TEST pattern.
     return DAG.getNode(X86ISD::CMP, dl, MVT::i32, Op,