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Partially fix PR20058: reduce compile time for loop unrolling with very high count by reducing calls to SE->forgetLoop
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212782 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -795,7 +795,8 @@ namespace llvm {
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/// forgetLoop - This method should be called by the client when it has
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/// changed a loop in a way that may effect ScalarEvolution's ability to
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/// compute a trip count, or if the loop is deleted.
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/// compute a trip count, or if the loop is deleted. This call is
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/// potentially expensive for large loop bodies.
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void forgetLoop(const Loop *L);
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/// forgetValue - This method should be called by the client when it has
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@ -17,6 +17,7 @@
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/UnrollLoop.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopIterator.h"
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@ -64,10 +65,15 @@ static inline void RemapInstruction(Instruction *I,
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/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it
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/// only has one predecessor, and that predecessor only has one successor.
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/// The LoopInfo Analysis that is passed will be kept consistent.
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/// Returns the new combined block.
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static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI,
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LPPassManager *LPM) {
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/// The LoopInfo Analysis that is passed will be kept consistent. If folding is
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/// successful references to the containing loop must be removed from
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/// ScalarEvolution by calling ScalarEvolution::forgetLoop because SE may have
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/// references to the eliminated BB. The argument ForgottenLoops contains a set
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/// of loops that have already been forgotten to prevent redundant, expensive
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/// calls to ScalarEvolution::forgetLoop. Returns the new combined block.
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static BasicBlock *
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FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI, LPPassManager *LPM,
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SmallPtrSetImpl<Loop *> &ForgottenLoops) {
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// Merge basic blocks into their predecessor if there is only one distinct
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// pred, and if there is only one distinct successor of the predecessor, and
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// if there are no PHI nodes.
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@ -104,8 +110,10 @@ static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI,
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// ScalarEvolution holds references to loop exit blocks.
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if (LPM) {
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if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>()) {
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if (Loop *L = LI->getLoopFor(BB))
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SE->forgetLoop(L);
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if (Loop *L = LI->getLoopFor(BB)) {
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if (ForgottenLoops.insert(L))
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SE->forgetLoop(L);
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}
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}
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}
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LI->removeBlock(BB);
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@ -423,11 +431,13 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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}
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// Merge adjacent basic blocks, if possible.
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SmallPtrSet<Loop *, 4> ForgottenLoops;
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for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
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BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
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if (Term->isUnconditional()) {
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BasicBlock *Dest = Term->getSuccessor(0);
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if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM))
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if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM,
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ForgottenLoops))
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std::replace(Latches.begin(), Latches.end(), Dest, Fold);
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}
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}
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