[llvm] r300239 - [ValueTracking] Prevent a call to computeKnownBits if we already know the state of the bit we would calculate. Also reuse a temporary APInt instead of creating a new one.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Apr 13 14:04:45 2017
New Revision: 300239

URL: http://llvm.org/viewvc/llvm-project?rev=300239&view=rev
Log:
[ValueTracking] Prevent a call to computeKnownBits if we already know the state of the bit we would calculate. Also reuse a temporary APInt instead of creating a new one.

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=300239&r1=300238&r2=300239&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Thu Apr 13 14:04:45 2017
@@ -918,13 +918,14 @@ static void computeKnownBitsFromOperator
     // TODO: This could be generalized to clearing any bit set in y where the
     // following bit is known to be unset in y.
     Value *Y = nullptr;
-    if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)),
-                                      m_Value(Y))) ||
-        match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)),
-                                      m_Value(Y)))) {
-      APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0);
-      computeKnownBits(Y, KnownZero3, KnownOne3, Depth + 1, Q);
-      if (KnownOne3.countTrailingOnes() > 0)
+    if (!KnownZero[0] && !KnownOne[0] &&
+        (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)),
+                                       m_Value(Y))) ||
+         match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)),
+                                       m_Value(Y))))) {
+      KnownZero2.clearAllBits(); KnownOne2.clearAllBits();
+      computeKnownBits(Y, KnownZero2, KnownOne2, Depth + 1, Q);
+      if (KnownOne2.countTrailingOnes() > 0)
         KnownZero.setBit(0);
     }
     break;