[llvm-commits] [llvm] r76524 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Dan Gohman]

Author: djg
Date: Mon Jul 20 19:42:47 2009
New Revision: 76524

URL: http://llvm.org/viewvc/llvm-project?rev=76524&view=rev
Log:
Make the range calculations for addrecs to be more conservative,
as they aren't currently prepared to handle complicated overflow
cases.

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=76524&r1=76523&r2=76524&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Jul 20 19:42:47 2009
@@ -2619,10 +2619,15 @@
         MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty);
 
         const SCEV *Start = AddRec->getStart();
+        const SCEV *Step = AddRec->getStepRecurrence(*this);
         const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
 
         // Check for overflow.
-        if (!isKnownPredicate(ICmpInst::ICMP_ULE, Start, End))
+        // TODO: This is very conservative.
+        if (!(Step->isOne() &&
+              isKnownPredicate(ICmpInst::ICMP_ULT, Start, End)) &&
+            !(Step->isAllOnesValue() &&
+              isKnownPredicate(ICmpInst::ICMP_UGT, Start, End)))
           return FullSet;
 
         ConstantRange StartRange = getUnsignedRange(Start);
@@ -2728,9 +2733,10 @@
         const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
 
         // Check for overflow.
-        if (!(isKnownPositive(Step) &&
+        // TODO: This is very conservative.
+        if (!(Step->isOne() &&
               isKnownPredicate(ICmpInst::ICMP_SLT, Start, End)) &&
-            !(isKnownNegative(Step) &&
+            !(Step->isAllOnesValue() &&
               isKnownPredicate(ICmpInst::ICMP_SGT, Start, End)))
           return FullSet;