From bfaa63a82eb84ed59573a8cb77ccd3e0d2b01bb0 Mon Sep 17 00:00:00 2001 From: Johannes Doerfert Date: Fri, 29 Apr 2016 10:36:58 +0000 Subject: [PATCH] [FIX] Prevent division/modulo by zero in parameters When we materialize parameter SCEVs we did so without considering the side effects they might have, e.g., both division and modulo are undefined if the right hand side is zero. This is a problem because we potentially extended the domain under which we evaluate parameters, thus we might have introduced such undefined behaviour. To prevent that from happening we will now guard divisions and modulo operations in the parameters with a compare and select. llvm-svn: 268023 --- polly/lib/Support/ScopHelper.cpp | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/polly/lib/Support/ScopHelper.cpp b/polly/lib/Support/ScopHelper.cpp index e73946f50426..a5c292be579a 100644 --- a/polly/lib/Support/ScopHelper.cpp +++ b/polly/lib/Support/ScopHelper.cpp @@ -246,6 +246,15 @@ private: const Region &R; ValueMapT *VMap; + /// @brief Return the Value for @p E if it is not zero or else the value 1. + Value *selectOneIfZero(const SCEV *E, Instruction *IP) { + auto *Ty = E->getType(); + auto *RHS = Expander.expandCodeFor(E, Ty, IP); + auto *Zero = ConstantInt::get(Ty, 0); + auto *Cond = new ICmpInst(IP, ICmpInst::ICMP_NE, RHS, Zero); + return SelectInst::Create(Cond, RHS, ConstantInt::get(Ty, 1), "", IP); + } + const SCEV *visitUnknown(const SCEVUnknown *E) { // If a value mapping was given try if the underlying value is remapped. @@ -273,7 +282,11 @@ private: const SCEV *RHSScev = visit(SE.getSCEV(Inst->getOperand(1))); Value *LHS = Expander.expandCodeFor(LHSScev, E->getType(), StartIP); - Value *RHS = Expander.expandCodeFor(RHSScev, E->getType(), StartIP); + Value *RHS = nullptr; + if (SE.isKnownNonZero(RHSScev)) + RHS = Expander.expandCodeFor(RHSScev, E->getType(), StartIP); + else + RHS = selectOneIfZero(RHSScev, StartIP); Inst = BinaryOperator::Create((Instruction::BinaryOps)Inst->getOpcode(), LHS, RHS, Inst->getName() + Name, StartIP); @@ -295,7 +308,12 @@ private: return SE.getSignExtendExpr(visit(E->getOperand()), E->getType()); } const SCEV *visitUDivExpr(const SCEVUDivExpr *E) { - return SE.getUDivExpr(visit(E->getLHS()), visit(E->getRHS())); + if (SE.isKnownNonZero(E->getRHS())) + return SE.getUDivExpr(visit(E->getLHS()), visit(E->getRHS())); + auto *RHSScev = visit(E->getRHS()); + auto *IP = R.getEnteringBlock()->getTerminator(); + auto *RHS = selectOneIfZero(RHSScev, IP); + return SE.getUDivExpr(visit(E->getLHS()), SE.getSCEV(RHS)); } const SCEV *visitAddExpr(const SCEVAddExpr *E) { SmallVector NewOps;