From 1d2c27b23eceec7b6a79e3f0b21d24068fbd50f3 Mon Sep 17 00:00:00 2001 From: Wojciech Matyjewicz Date: Tue, 12 Feb 2008 15:09:36 +0000 Subject: 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. llvm-svn: 47007 --- llvm/lib/Analysis/ScalarEvolution.cpp | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'llvm/lib/Analysis/ScalarEvolution.cpp') diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp index 122dba3e6ac..65cee82a964 100644 --- a/llvm/lib/Analysis/ScalarEvolution.cpp +++ b/llvm/lib/Analysis/ScalarEvolution.cpp @@ -2527,19 +2527,17 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L, bool isSigned) { 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; -- cgit v1.2.3