Fix PR2002. Suppose n is the initial value for the induction
variable (with step 1) and m is its final value. Then, the correct trip
count is SMAX(m,n)-n. Previously, we used SMAX(0,m-n), but m-n may
overflow and can't in general be interpreted as signed.
Patch by Nick Lewycky.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47007 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 122dba3..65cee82 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2527,19 +2527,17 @@
if (AddRec->isAffine()) {
// The number of iterations for "{n,+,1} < m", is m-n. However, we don't
// know that m is >= n on input to the loop. If it is, the condition
- // returns true zero times. To handle both cases, we return SMAX(0, m-n).
+ // returns true zero times. To handle both cases, we return SMAX(m, n)-n.
// FORNOW: We only support unit strides.
SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
if (AddRec->getOperand(1) != One)
return UnknownValue;
- SCEVHandle Iters = SE.getMinusSCEV(RHS, AddRec->getOperand(0));
+ SCEVHandle Start = AddRec->getOperand(0);
+ SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start) : (SCEVHandle)RHS;
- if (isSigned)
- return SE.getSMaxExpr(SE.getIntegerSCEV(0, RHS->getType()), Iters);
- else
- return Iters;
+ return SE.getMinusSCEV(End, Start);
}
return UnknownValue;