[llvm] r338492 - [X86] When looking for (CMOV C-1, (ADD (CTTZ X), C), (X != 0)) -> (ADD (CMOV (CTTZ X), -1, (X != 0)), C), make sure we really have a compare with 0.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Tue Jul 31 23:36:20 2018
New Revision: 338492

URL: http://llvm.org/viewvc/llvm-project?rev=338492&view=rev
Log:
[X86] When looking for (CMOV C-1, (ADD (CTTZ X), C), (X != 0)) -> (ADD (CMOV (CTTZ X), -1, (X != 0)), C), make sure we really have a compare with 0.

It's not strictly required by the transform of the cmov and the add, but it makes sure we restrict it to the cases we know we want to match.

While there canonicalize the operand order of the cmov to simplify the matching and emitting code.

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=338492&r1=338491&r2=338492&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Tue Jul 31 23:36:20 2018
@@ -33445,33 +33445,32 @@ static SDValue combineCMov(SDNode *N, Se
     }
   }
 
-  // Handle (CMOV C-1, (ADD (CTTZ X), C), (X != 0)) ->
-  // (ADD (CMOV (CTTZ X), -1, (X != 0)), C) or
-  // (CMOV (ADD (CTTZ X), C), C-1, (X == 0)) ->
-  // (ADD (CMOV C-1, (CTTZ X), (X == 0)), C)
-  if (CC == X86::COND_NE || CC == X86::COND_E) {
-    auto *Cnst = CC == X86::COND_E ? dyn_cast<ConstantSDNode>(TrueOp)
-                                   : dyn_cast<ConstantSDNode>(FalseOp);
-    SDValue Add = CC == X86::COND_E ? FalseOp : TrueOp;
+  // Fold (CMOV C1, (ADD (CTTZ X), C2), (X != 0)) ->
+  //      (ADD (CMOV C1-C2, (CTTZ X), (X != 0)), C2)
+  // Or (CMOV (ADD (CTTZ X), C2), C1, (X == 0)) ->
+  //    (ADD (CMOV (CTTZ X), C1-C2, (X == 0)), C2)
+  if ((CC == X86::COND_NE || CC == X86::COND_E) &&
+      Cond.getOpcode() == X86ISD::CMP && isNullConstant(Cond.getOperand(1))) {
+    SDValue Add = TrueOp;
+    SDValue Const = FalseOp;
+    // Canonicalize the condition code for easier matching and output.
+    if (CC == X86::COND_E) {
+      std::swap(Add, Const);
+      CC = X86::COND_NE;
+    }
 
-    if (Cnst && Add.getOpcode() == ISD::ADD && Add.hasOneUse()) {
-      auto *AddOp1 = dyn_cast<ConstantSDNode>(Add.getOperand(1));
-      SDValue AddOp2 = Add.getOperand(0);
-      if (AddOp1 && (AddOp2.getOpcode() == ISD::CTTZ_ZERO_UNDEF ||
-                     AddOp2.getOpcode() == ISD::CTTZ)) {
-        APInt Diff = Cnst->getAPIntValue() - AddOp1->getAPIntValue();
-        if (CC == X86::COND_E) {
-          Add = DAG.getNode(X86ISD::CMOV, DL, Add.getValueType(), AddOp2,
-                            DAG.getConstant(Diff, DL, Add.getValueType()),
-                            DAG.getConstant(CC, DL, MVT::i8), Cond);
-        } else {
-          Add = DAG.getNode(X86ISD::CMOV, DL, Add.getValueType(),
-                            DAG.getConstant(Diff, DL, Add.getValueType()),
-                            AddOp2, DAG.getConstant(CC, DL, MVT::i8), Cond);
-        }
-        return DAG.getNode(X86ISD::ADD, DL, Add.getValueType(), Add,
-                           SDValue(AddOp1, 0));
-      }
+    // Ok, now make sure that Add is (add (cttz X), C2) and Const is a constant.
+    if (isa<ConstantSDNode>(Const) && Add.getOpcode() == ISD::ADD &&
+        Add.hasOneUse() && isa<ConstantSDNode>(Add.getOperand(1)) &&
+        (Add.getOperand(0).getOpcode() == ISD::CTTZ_ZERO_UNDEF ||
+         Add.getOperand(0).getOpcode() == ISD::CTTZ) &&
+        Add.getOperand(0).getOperand(0) == Cond.getOperand(0)) {
+      EVT VT = N->getValueType(0);
+      // This should constant fold.
+      SDValue Diff = DAG.getNode(ISD::SUB, DL, VT, Const, Add.getOperand(1));
+      SDValue CMov = DAG.getNode(X86ISD::CMOV, DL, VT, Diff, Add.getOperand(0),
+                                 DAG.getConstant(CC, DL, MVT::i8), Cond);
+      return DAG.getNode(ISD::ADD, DL, VT, CMov, Add.getOperand(1));
     }
   }