[llvm-commits] [llvm] r101028 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Dan Gohman]

Author: djg
Date: Mon Apr 12 02:39:33 2010
New Revision: 101028

URL: http://llvm.org/viewvc/llvm-project?rev=101028&view=rev
Log:
Rewrite the overflow checking in the get{Signed,Unsigned}Range code for
AddRecs so that it checks for overflow in the computation that it is
performing, rather than just checking hasNo{Signed,Unsigned}Wrap, since
those flags are for a different computation. This fixes a bug that
impacts an upcoming change.

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

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=101028&r1=101027&r2=101028&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Apr 12 02:39:33 2010
@@ -2933,14 +2933,26 @@
         MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty);
 
         const SCEV *Start = AddRec->getStart();
-        const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
+        const SCEV *Step = AddRec->getStepRecurrence(*this);
 
-        // Check for overflow.
-        if (!AddRec->hasNoUnsignedWrap())
+        ConstantRange StartRange = getUnsignedRange(Start);
+        ConstantRange StepRange = getSignedRange(Step);
+        ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount);
+        ConstantRange EndRange =
+          StartRange.add(MaxBECountRange.multiply(StepRange));
+
+        // Check for overflow. This must be done with ConstantRange arithmetic
+        // because we could be called from within the ScalarEvolution overflow
+        // checking code.
+        ConstantRange ExtStartRange = StartRange.zextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtMaxBECountRange =
+          MaxBECountRange.zextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtEndRange = EndRange.zextOrTrunc(BitWidth*2+1);
+        if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) !=
+            ExtEndRange)
           return ConservativeResult;
 
-        ConstantRange StartRange = getUnsignedRange(Start);
-        ConstantRange EndRange = getUnsignedRange(End);
         APInt Min = APIntOps::umin(StartRange.getUnsignedMin(),
                                    EndRange.getUnsignedMin());
         APInt Max = APIntOps::umax(StartRange.getUnsignedMax(),
@@ -3064,14 +3076,26 @@
         MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty);
 
         const SCEV *Start = AddRec->getStart();
-        const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
+        const SCEV *Step = AddRec->getStepRecurrence(*this);
 
-        // Check for overflow.
-        if (!AddRec->hasNoSignedWrap())
+        ConstantRange StartRange = getSignedRange(Start);
+        ConstantRange StepRange = getSignedRange(Step);
+        ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount);
+        ConstantRange EndRange =
+          StartRange.add(MaxBECountRange.multiply(StepRange));
+
+        // Check for overflow. This must be done with ConstantRange arithmetic
+        // because we could be called from within the ScalarEvolution overflow
+        // checking code.
+        ConstantRange ExtStartRange = StartRange.sextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtMaxBECountRange =
+          MaxBECountRange.zextOrTrunc(BitWidth*2+1);
+        ConstantRange ExtEndRange = EndRange.sextOrTrunc(BitWidth*2+1);
+        if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) !=
+            ExtEndRange)
           return ConservativeResult;
 
-        ConstantRange StartRange = getSignedRange(Start);
-        ConstantRange EndRange = getSignedRange(End);
         APInt Min = APIntOps::smin(StartRange.getSignedMin(),
                                    EndRange.getSignedMin());
         APInt Max = APIntOps::smax(StartRange.getSignedMax(),