forked from OSchip/llvm-project
Extend ScalarEvolution's executesAtLeastOnce logic to be able to
continue past the first conditional branch when looking for a relevant test. This helps it avoid using MAX expressions in loop trip counts in more cases. llvm-svn: 54697
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@ -2709,66 +2709,68 @@ bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool isSigned,
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SCEV *LHS, SCEV *RHS) {
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BasicBlock *Preheader = L->getLoopPreheader();
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BasicBlock *PreheaderDest = L->getHeader();
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if (Preheader == 0) return false;
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BranchInst *LoopEntryPredicate =
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dyn_cast<BranchInst>(Preheader->getTerminator());
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if (!LoopEntryPredicate) return false;
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// Starting at the preheader, climb up the predecessor chain, as long as
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// there are unique predecessors, looking for a conditional branch that
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// protects the loop.
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//
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// This is a conservative apporoximation of a climb of the
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// control-dependence predecessors.
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// This might be a critical edge broken out. If the loop preheader ends in
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// an unconditional branch to the loop, check to see if the preheader has a
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// single predecessor, and if so, look for its terminator.
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while (LoopEntryPredicate->isUnconditional()) {
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PreheaderDest = Preheader;
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Preheader = Preheader->getSinglePredecessor();
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if (!Preheader) return false; // Multiple preds.
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LoopEntryPredicate =
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for (; Preheader; PreheaderDest = Preheader,
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Preheader = Preheader->getSinglePredecessor()) {
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BranchInst *LoopEntryPredicate =
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dyn_cast<BranchInst>(Preheader->getTerminator());
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if (!LoopEntryPredicate) return false;
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if (!LoopEntryPredicate ||
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LoopEntryPredicate->isUnconditional())
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continue;
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ICmpInst *ICI = dyn_cast<ICmpInst>(LoopEntryPredicate->getCondition());
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if (!ICI) continue;
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// Now that we found a conditional branch that dominates the loop, check to
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// see if it is the comparison we are looking for.
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Value *PreCondLHS = ICI->getOperand(0);
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Value *PreCondRHS = ICI->getOperand(1);
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ICmpInst::Predicate Cond;
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if (LoopEntryPredicate->getSuccessor(0) == PreheaderDest)
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Cond = ICI->getPredicate();
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else
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Cond = ICI->getInversePredicate();
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switch (Cond) {
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case ICmpInst::ICMP_UGT:
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if (isSigned) continue;
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std::swap(PreCondLHS, PreCondRHS);
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Cond = ICmpInst::ICMP_ULT;
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break;
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case ICmpInst::ICMP_SGT:
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if (!isSigned) continue;
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std::swap(PreCondLHS, PreCondRHS);
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Cond = ICmpInst::ICMP_SLT;
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break;
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case ICmpInst::ICMP_ULT:
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if (isSigned) continue;
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break;
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case ICmpInst::ICMP_SLT:
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if (!isSigned) continue;
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break;
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default:
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continue;
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}
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if (!PreCondLHS->getType()->isInteger()) continue;
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SCEVHandle PreCondLHSSCEV = getSCEV(PreCondLHS);
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SCEVHandle PreCondRHSSCEV = getSCEV(PreCondRHS);
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if ((LHS == PreCondLHSSCEV && RHS == PreCondRHSSCEV) ||
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(LHS == SE.getNotSCEV(PreCondRHSSCEV) &&
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RHS == SE.getNotSCEV(PreCondLHSSCEV)))
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return true;
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}
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ICmpInst *ICI = dyn_cast<ICmpInst>(LoopEntryPredicate->getCondition());
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if (!ICI) return false;
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// Now that we found a conditional branch that dominates the loop, check to
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// see if it is the comparison we are looking for.
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Value *PreCondLHS = ICI->getOperand(0);
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Value *PreCondRHS = ICI->getOperand(1);
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ICmpInst::Predicate Cond;
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if (LoopEntryPredicate->getSuccessor(0) == PreheaderDest)
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Cond = ICI->getPredicate();
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else
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Cond = ICI->getInversePredicate();
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switch (Cond) {
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case ICmpInst::ICMP_UGT:
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if (isSigned) return false;
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std::swap(PreCondLHS, PreCondRHS);
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Cond = ICmpInst::ICMP_ULT;
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break;
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case ICmpInst::ICMP_SGT:
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if (!isSigned) return false;
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std::swap(PreCondLHS, PreCondRHS);
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Cond = ICmpInst::ICMP_SLT;
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break;
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case ICmpInst::ICMP_ULT:
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if (isSigned) return false;
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break;
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case ICmpInst::ICMP_SLT:
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if (!isSigned) return false;
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break;
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default:
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return false;
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}
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if (!PreCondLHS->getType()->isInteger()) return false;
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SCEVHandle PreCondLHSSCEV = getSCEV(PreCondLHS);
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SCEVHandle PreCondRHSSCEV = getSCEV(PreCondRHS);
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return (LHS == PreCondLHSSCEV && RHS == PreCondRHSSCEV) ||
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(LHS == SE.getNotSCEV(PreCondRHSSCEV) &&
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RHS == SE.getNotSCEV(PreCondLHSSCEV));
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return false;
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}
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/// HowManyLessThans - Return the number of times a backedge containing the
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@ -0,0 +1,35 @@
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; RUN: llvm-as < %s | opt -scalar-evolution -analyze | grep {Loop bb3: ( -1 + %n) iterations!}
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; We don't want to use a max in the trip count expression in
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; this testcase.
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define void @foo(i32 %n, i32* %p, i32* %q) nounwind {
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entry:
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icmp sgt i32 %n, 0
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br i1 %0, label %bb, label %return
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bb:
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load i32* %q, align 4
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icmp eq i32 %1, 0
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br i1 %2, label %return, label %bb3.preheader
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bb3.preheader:
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br label %bb3
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bb3:
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%i.0 = phi i32 [ %7, %bb3 ], [ 0, %bb3.preheader ]
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getelementptr i32* %p, i32 %i.0
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load i32* %3, align 4
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add i32 %4, 1
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getelementptr i32* %p, i32 %i.0
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store i32 %5, i32* %6, align 4
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add i32 %i.0, 1
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icmp slt i32 %7, %n
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br i1 %8, label %bb3, label %return.loopexit
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return.loopexit:
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br label %return
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return:
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ret void
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}
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