[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Zhou Sheng]

Changes in directory llvm/lib/Transforms/Scalar:

InstructionCombining.cpp updated: 1.660 -> 1.661
---
Log message:

ShiftAmt might equal to zero. Handle this situation.


---
Diffs of the changes:  (+9 -7)

 InstructionCombining.cpp |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)


Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.660 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.661
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.660	Tue Mar 13 22:21:24 2007
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Wed Mar 14 04:07:33 2007
@@ -1997,7 +1997,8 @@
       RHSKnownZero <<= ShiftAmt;
       RHSKnownOne  <<= ShiftAmt;
       // low bits known zero.
-      RHSKnownZero |= APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth);
+      if (ShiftAmt)
+        RHSKnownZero |= APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth);
     }
     break;
   case Instruction::LShr:
@@ -2013,14 +2014,16 @@
         return true;
       assert((RHSKnownZero & RHSKnownOne) == 0 && 
              "Bits known to be one AND zero?"); 
-      // Compute the new bits that are at the top now.
-      APInt HighBits(APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth).shl(
-              BitWidth - ShiftAmt));
       RHSKnownZero &= TypeMask;
       RHSKnownOne  &= TypeMask;
       RHSKnownZero = APIntOps::lshr(RHSKnownZero, ShiftAmt);
       RHSKnownOne  = APIntOps::lshr(RHSKnownOne, ShiftAmt);
-      RHSKnownZero |= HighBits;  // high bits known zero.
+      if (ShiftAmt) {
+        // Compute the new bits that are at the top now.
+        APInt HighBits(APInt::getAllOnesValue(BitWidth).shl(
+                         BitWidth - ShiftAmt));
+        RHSKnownZero |= HighBits;  // high bits known zero.
+      }
     }
     break;
   case Instruction::AShr:
@@ -2048,8 +2051,7 @@
       assert((RHSKnownZero & RHSKnownOne) == 0 && 
              "Bits known to be one AND zero?"); 
       // Compute the new bits that are at the top now.
-      APInt HighBits(APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth).shl(
-              BitWidth - ShiftAmt));
+      APInt HighBits(APInt::getAllOnesValue(BitWidth).shl(BitWidth - ShiftAmt));
       RHSKnownZero &= TypeMask;
       RHSKnownOne  &= TypeMask;
       RHSKnownZero = APIntOps::lshr(RHSKnownZero, ShiftAmt);