[llvm] r312285 - [X86] Don't pull carry through X86ISD::ADD carryin, -1 if we can't guranteed we're really using the carry flag from the add.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Aug 31 14:39:23 2017
New Revision: 312285

URL: http://llvm.org/viewvc/llvm-project?rev=312285&view=rev
Log:
[X86] Don't pull carry through X86ISD::ADD carryin, -1 if we can't guranteed we're really using the carry flag from the add.

Prior to this patch we had a DAG combine that tried to bypass an X86ISD::ADD with -1 being added to the carry flag of some previous operation. We would then pass the carry flag directly to user.

But this is only safe if the user is looking for the carry flag and not the zero flag.

So we need to only do this combine in a context where we know what flag the consumer is using.

Fixes PR34381.

Differential Revision: https://reviews.llvm.org/D37317

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=312285&r1=312284&r2=312285&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Thu Aug 31 14:39:23 2017
@@ -30939,11 +30939,40 @@ static bool checkBoolTestAndOrSetCCCombi
   return true;
 }
 
+// When legalizing carry, we create carries via add X, -1
+// If that comes from an actual carry, via setcc, we use the
+// carry directly.
+static SDValue combineCarryThroughADD(SDValue EFLAGS) {
+  if (EFLAGS.getOpcode() == X86ISD::ADD) {
+    if (isAllOnesConstant(EFLAGS.getOperand(1))) {
+      SDValue Carry = EFLAGS.getOperand(0);
+      while (Carry.getOpcode() == ISD::TRUNCATE ||
+             Carry.getOpcode() == ISD::ZERO_EXTEND ||
+             Carry.getOpcode() == ISD::SIGN_EXTEND ||
+             Carry.getOpcode() == ISD::ANY_EXTEND ||
+             (Carry.getOpcode() == ISD::AND &&
+              isOneConstant(Carry.getOperand(1))))
+        Carry = Carry.getOperand(0);
+      if (Carry.getOpcode() == X86ISD::SETCC ||
+          Carry.getOpcode() == X86ISD::SETCC_CARRY) {
+        if (Carry.getConstantOperandVal(0) == X86::COND_B)
+          return Carry.getOperand(1);
+      }
+    }
+  }
+
+  return SDValue();
+}
+
 /// Optimize an EFLAGS definition used according to the condition code \p CC
 /// into a simpler EFLAGS value, potentially returning a new \p CC and replacing
 /// uses of chain values.
 static SDValue combineSetCCEFLAGS(SDValue EFLAGS, X86::CondCode &CC,
                                   SelectionDAG &DAG) {
+  if (CC == X86::COND_B)
+    if (SDValue Flags = combineCarryThroughADD(EFLAGS))
+      return Flags;
+
   if (SDValue R = checkBoolTestSetCCCombine(EFLAGS, CC))
     return R;
   return combineSetCCAtomicArith(EFLAGS, CC, DAG);
@@ -34987,27 +35016,13 @@ static SDValue combineSIntToFP(SDNode *N
   return SDValue();
 }
 
-// Optimize RES, EFLAGS = X86ISD::ADD LHS, RHS
-static SDValue combineX86ADD(SDNode *N, SelectionDAG &DAG,
-                             X86TargetLowering::DAGCombinerInfo &DCI) {
-  // When legalizing carry, we create carries via add X, -1
-  // If that comes from an actual carry, via setcc, we use the
-  // carry directly.
-  if (isAllOnesConstant(N->getOperand(1)) && N->hasAnyUseOfValue(1)) {
-    SDValue Carry = N->getOperand(0);
-    while (Carry.getOpcode() == ISD::TRUNCATE ||
-           Carry.getOpcode() == ISD::ZERO_EXTEND ||
-           Carry.getOpcode() == ISD::SIGN_EXTEND ||
-           Carry.getOpcode() == ISD::ANY_EXTEND ||
-           (Carry.getOpcode() == ISD::AND &&
-            isOneConstant(Carry.getOperand(1))))
-      Carry = Carry.getOperand(0);
-
-    if (Carry.getOpcode() == X86ISD::SETCC ||
-        Carry.getOpcode() == X86ISD::SETCC_CARRY) {
-      if (Carry.getConstantOperandVal(0) == X86::COND_B)
-        return DCI.CombineTo(N, SDValue(N, 0), Carry.getOperand(1));
-    }
+static SDValue combineSBB(SDNode *N, SelectionDAG &DAG) {
+  if (SDValue Flags = combineCarryThroughADD(N->getOperand(2))) {
+    MVT VT = N->getSimpleValueType(0);
+    SDVTList VTs = DAG.getVTList(VT, MVT::i32);
+    return DAG.getNode(X86ISD::SBB, SDLoc(N), VTs,
+                       N->getOperand(0), N->getOperand(1),
+                       Flags);
   }
 
   return SDValue();
@@ -35036,6 +35051,14 @@ static SDValue combineADC(SDNode *N, Sel
     return DCI.CombineTo(N, Res1, CarryOut);
   }
 
+  if (SDValue Flags = combineCarryThroughADD(N->getOperand(2))) {
+    MVT VT = N->getSimpleValueType(0);
+    SDVTList VTs = DAG.getVTList(VT, MVT::i32);
+    return DAG.getNode(X86ISD::ADC, SDLoc(N), VTs,
+                       N->getOperand(0), N->getOperand(1),
+                       Flags);
+  }
+
   return SDValue();
 }
 
@@ -35721,7 +35744,7 @@ SDValue X86TargetLowering::PerformDAGCom
   case X86ISD::CMOV:        return combineCMov(N, DAG, DCI, Subtarget);
   case ISD::ADD:            return combineAdd(N, DAG, Subtarget);
   case ISD::SUB:            return combineSub(N, DAG, Subtarget);
-  case X86ISD::ADD:         return combineX86ADD(N, DAG, DCI);
+  case X86ISD::SBB:         return combineSBB(N, DAG);
   case X86ISD::ADC:         return combineADC(N, DAG, DCI);
   case ISD::MUL:            return combineMul(N, DAG, DCI, Subtarget);
   case ISD::SHL: