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Partially fix PR20058: reduce compile time for loop unrolling with very high count by reducing calls to SE->forgetLoop

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212782 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Mark Heffernan 2014-07-10 23:30:06 +00:00
parent eb2fff64dd
commit 9853f94520
2 changed files with 19 additions and 8 deletions
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3
include/llvm/Analysis/ScalarEvolution.h
View File

@ -795,7 +795,8 @@ namespace llvm {
/// forgetLoop - This method should be called by the client when it has
/// changed a loop in a way that may effect ScalarEvolution's ability to
/// compute a trip count, or if the loop is deleted.
/// compute a trip count, or if the loop is deleted. This call is
/// potentially expensive for large loop bodies.
void forgetLoop(const Loop *L);
/// forgetValue - This method should be called by the client when it has

24
lib/Transforms/Utils/LoopUnroll.cpp
View File

@ -17,6 +17,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/UnrollLoop.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopIterator.h"
@ -64,10 +65,15 @@ static inline void RemapInstruction(Instruction *I,
/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it
/// only has one predecessor, and that predecessor only has one successor.
/// The LoopInfo Analysis that is passed will be kept consistent.
/// Returns the new combined block.
static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI,
LPPassManager *LPM) {
/// The LoopInfo Analysis that is passed will be kept consistent. If folding is
/// successful references to the containing loop must be removed from
/// ScalarEvolution by calling ScalarEvolution::forgetLoop because SE may have
/// references to the eliminated BB. The argument ForgottenLoops contains a set
/// of loops that have already been forgotten to prevent redundant, expensive
/// calls to ScalarEvolution::forgetLoop. Returns the new combined block.
static BasicBlock *
FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI, LPPassManager *LPM,
SmallPtrSetImpl<Loop *> &ForgottenLoops) {
// Merge basic blocks into their predecessor if there is only one distinct
// pred, and if there is only one distinct successor of the predecessor, and
// if there are no PHI nodes.
@ -104,8 +110,10 @@ static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI,
// ScalarEvolution holds references to loop exit blocks.
if (LPM) {
if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>()) {
if (Loop *L = LI->getLoopFor(BB))
SE->forgetLoop(L);
if (Loop *L = LI->getLoopFor(BB)) {
if (ForgottenLoops.insert(L))
SE->forgetLoop(L);
}
}
}
LI->removeBlock(BB);
@ -423,11 +431,13 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
}
// Merge adjacent basic blocks, if possible.
SmallPtrSet<Loop *, 4> ForgottenLoops;
for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
if (Term->isUnconditional()) {
BasicBlock *Dest = Term->getSuccessor(0);
if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM))
if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI, LPM,
ForgottenLoops))
std::replace(Latches.begin(), Latches.end(), Dest, Fold);
}
}