[llvm] r290490 - [SelectionDAG] Early out from computeKnownBits when we know we will have no common bits.

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Sat Dec 24 06:59:35 2016
New Revision: 290490

URL: http://llvm.org/viewvc/llvm-project?rev=290490&view=rev
Log:
[SelectionDAG] Early out from computeKnownBits when we know we will have no common bits.

Avoid extra (recursive) calls to computeKnownBits if we already know that there are no common known bits.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=290490&r1=290489&r2=290490&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Sat Dec 24 06:59:35 2016
@@ -2087,7 +2087,10 @@ void SelectionDAG::computeKnownBits(SDVa
       if (M < 0) {
         // For UNDEF elements, we don't know anything about the common state of
         // the shuffle result.
-        KnownZero = KnownOne = APInt(BitWidth, 0);
+        KnownOne.clearAllBits();
+        KnownZero.clearAllBits();
+        DemandedLHS.clearAllBits();
+        DemandedRHS.clearAllBits();
         break;
       }
 
@@ -2103,6 +2106,9 @@ void SelectionDAG::computeKnownBits(SDVa
       KnownOne &= KnownOne2;
       KnownZero &= KnownZero2;
     }
+    // If we don't know any bits, early out.
+    if (!KnownOne && !KnownZero)
+      break;
     if (!!DemandedRHS) {
       SDValue RHS = Op.getOperand(1);
       computeKnownBits(RHS, KnownZero2, KnownOne2, DemandedRHS, Depth + 1);
@@ -2126,6 +2132,9 @@ void SelectionDAG::computeKnownBits(SDVa
         KnownOne &= KnownOne2;
         KnownZero &= KnownZero2;
       }
+      // If we don't know any bits, early out.
+      if (!KnownOne && !KnownZero)
+        break;
     }
     break;
   }
@@ -2207,6 +2216,9 @@ void SelectionDAG::computeKnownBits(SDVa
           unsigned Offset = (i % SubScale) * BitWidth;
           KnownOne &= KnownOne2.lshr(Offset).trunc(BitWidth);
           KnownZero &= KnownZero2.lshr(Offset).trunc(BitWidth);
+          // If we don't know any bits, early out.
+          if (!KnownOne && !KnownZero)
+            break;
         }
     }
     break;
@@ -2290,6 +2302,9 @@ void SelectionDAG::computeKnownBits(SDVa
   }
   case ISD::SELECT:
     computeKnownBits(Op.getOperand(2), KnownZero, KnownOne, Depth+1);
+    // If we don't know any bits, early out.
+    if (!KnownOne && !KnownZero)
+      break;
     computeKnownBits(Op.getOperand(1), KnownZero2, KnownOne2, Depth+1);
 
     // Only known if known in both the LHS and RHS.
@@ -2298,6 +2313,9 @@ void SelectionDAG::computeKnownBits(SDVa
     break;
   case ISD::SELECT_CC:
     computeKnownBits(Op.getOperand(3), KnownZero, KnownOne, Depth+1);
+    // If we don't know any bits, early out.
+    if (!KnownOne && !KnownZero)
+      break;
     computeKnownBits(Op.getOperand(2), KnownZero2, KnownOne2, Depth+1);
 
     // Only known if known in both the LHS and RHS.
@@ -2691,15 +2709,15 @@ void SelectionDAG::computeKnownBits(SDVa
   case ISD::SMAX:
   case ISD::UMIN:
   case ISD::UMAX: {
-    APInt Op0Zero, Op0One;
-    APInt Op1Zero, Op1One;
-    computeKnownBits(Op.getOperand(0), Op0Zero, Op0One, DemandedElts,
+    computeKnownBits(Op.getOperand(0), KnownZero, KnownOne, DemandedElts,
                      Depth + 1);
-    computeKnownBits(Op.getOperand(1), Op1Zero, Op1One, DemandedElts,
+    // If we don't know any bits, early out.
+    if (!KnownOne && !KnownZero)
+      break;
+    computeKnownBits(Op.getOperand(1), KnownZero2, KnownOne2, DemandedElts,
                      Depth + 1);
-
-    KnownZero = Op0Zero & Op1Zero;
-    KnownOne = Op0One & Op1One;
+    KnownZero &= KnownZero2;
+    KnownOne &= KnownOne2;
     break;
   }
   case ISD::FrameIndex: