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[LoopDeletion] Move deleteDeadLoop to to LoopUtils. NFC

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llvm-svn: 314934
This commit is contained in:
Marcello Maggioni 2017-10-04 20:42:46 +00:00
parent e01aed9846
commit e3a4a32d00
3 changed files with 138 additions and 134 deletions
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14
include/llvm/Transforms/Utils/LoopUtils.h
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@ -439,6 +439,20 @@ bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
TargetLibraryInfo *, Loop *, AliasSetTracker *,
LoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
/// This function deletes dead loops. The caller of this function needs to
/// guarantee that the loop is infact dead.
/// The function requires a bunch or prerequisites to be present:
/// - The loop needs to be in LCSSA form
/// - The loop needs to have a Preheader
/// - A unique dedicated exit block must exist
///
/// This also updates the relevant analysis information in \p DT, \p SE, and \p
/// LI if pointers to those are provided.
/// It also updates the loop PM if an updater struct is provided.
void deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
LoopInfo *LI);
/// \brief Try to promote memory values to scalars by sinking stores out of
/// the loop and moving loads to before the loop. We do this by looping over
/// the stores in the loop, looking for stores to Must pointers which are

136
lib/Transforms/Scalar/LoopDeletion.cpp
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@ -30,21 +30,6 @@ using namespace llvm;
STATISTIC(NumDeleted, "Number of loops deleted");
/// This function deletes dead loops. The caller of this function needs to
/// guarantee that the loop is infact dead. Here we handle two kinds of dead
/// loop. The first kind (\p isLoopDead) is where only invariant values from
/// within the loop are used outside of it. The second kind (\p
/// isLoopNeverExecuted) is where the loop is provably never executed. We can
/// always remove never executed loops since they will not cause any difference
/// to program behaviour.
///
/// This also updates the relevant analysis information in \p DT, \p SE, and \p
/// LI. It also updates the loop PM if an updater struct is provided.
// TODO: This function will be used by loop-simplifyCFG as well. So, move this
// to LoopUtils.cpp
static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
LoopInfo &LI);
enum class LoopDeletionResult {
Unmodified,
Modified,
@ -183,7 +168,7 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
P->setIncomingValue(i, UndefValue::get(P->getType()));
BI++;
}
deleteDeadLoop(L, DT, SE, LI);
deleteDeadLoop(L, &DT, &SE, &LI);
++NumDeleted;
return LoopDeletionResult::Deleted;
}
@ -219,129 +204,12 @@ static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
}
DEBUG(dbgs() << "Loop is invariant, delete it!");
deleteDeadLoop(L, DT, SE, LI);
deleteDeadLoop(L, &DT, &SE, &LI);
++NumDeleted;
return LoopDeletionResult::Deleted;
}
static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
LoopInfo &LI) {
assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
auto *Preheader = L->getLoopPreheader();
assert(Preheader && "Preheader should exist!");
// Now that we know the removal is safe, remove the loop by changing the
// branch from the preheader to go to the single exit block.
//
// Because we're deleting a large chunk of code at once, the sequence in which
// we remove things is very important to avoid invalidation issues.
// Tell ScalarEvolution that the loop is deleted. Do this before
// deleting the loop so that ScalarEvolution can look at the loop
// to determine what it needs to clean up.
SE.forgetLoop(L);
auto *ExitBlock = L->getUniqueExitBlock();
assert(ExitBlock && "Should have a unique exit block!");
assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
auto *OldBr = dyn_cast<BranchInst>(Preheader->getTerminator());
assert(OldBr && "Preheader must end with a branch");
assert(OldBr->isUnconditional() && "Preheader must have a single successor");
// Connect the preheader to the exit block. Keep the old edge to the header
// around to perform the dominator tree update in two separate steps
// -- #1 insertion of the edge preheader -> exit and #2 deletion of the edge
// preheader -> header.
//
//
// 0. Preheader 1. Preheader 2. Preheader
// | | | |
// V | V |
// Header <--\ | Header <--\ | Header <--\
// | | | | | | | | | | |
// | V | | | V | | | V |
// | Body --/ | | Body --/ | | Body --/
// V V V V V
// Exit Exit Exit
//
// By doing this is two separate steps we can perform the dominator tree
// update without using the batch update API.
//
// Even when the loop is never executed, we cannot remove the edge from the
// source block to the exit block. Consider the case where the unexecuted loop
// branches back to an outer loop. If we deleted the loop and removed the edge
// coming to this inner loop, this will break the outer loop structure (by
// deleting the backedge of the outer loop). If the outer loop is indeed a
// non-loop, it will be deleted in a future iteration of loop deletion pass.
IRBuilder<> Builder(OldBr);
Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
// Remove the old branch. The conditional branch becomes a new terminator.
OldBr->eraseFromParent();
// Update the dominator tree by informing it about the new edge from the
// preheader to the exit.
DT.insertEdge(Preheader, ExitBlock);
// Rewrite phis in the exit block to get their inputs from the Preheader
// instead of the exiting block.
BasicBlock::iterator BI = ExitBlock->begin();
while (PHINode *P = dyn_cast<PHINode>(BI)) {
// Set the zero'th element of Phi to be from the preheader and remove all
// other incoming values. Given the loop has dedicated exits, all other
// incoming values must be from the exiting blocks.
int PredIndex = 0;
P->setIncomingBlock(PredIndex, Preheader);
// Removes all incoming values from all other exiting blocks (including
// duplicate values from an exiting block).
// Nuke all entries except the zero'th entry which is the preheader entry.
// NOTE! We need to remove Incoming Values in the reverse order as done
// below, to keep the indices valid for deletion (removeIncomingValues
// updates getNumIncomingValues and shifts all values down into the operand
// being deleted).
for (unsigned i = 0, e = P->getNumIncomingValues() - 1; i != e; ++i)
P->removeIncomingValue(e-i, false);
assert((P->getNumIncomingValues() == 1 &&
P->getIncomingBlock(PredIndex) == Preheader) &&
"Should have exactly one value and that's from the preheader!");
++BI;
}
// Disconnect the loop body by branching directly to its exit.
Builder.SetInsertPoint(Preheader->getTerminator());
Builder.CreateBr(ExitBlock);
// Remove the old branch.
Preheader->getTerminator()->eraseFromParent();
// Inform the dominator tree about the removed edge.
DT.deleteEdge(Preheader, L->getHeader());
// Remove the block from the reference counting scheme, so that we can
// delete it freely later.
for (auto *Block : L->blocks())
Block->dropAllReferences();
// Erase the instructions and the blocks without having to worry
// about ordering because we already dropped the references.
// NOTE: This iteration is safe because erasing the block does not remove its
// entry from the loop's block list. We do that in the next section.
for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end();
LI != LE; ++LI)
(*LI)->eraseFromParent();
// Finally, the blocks from loopinfo. This has to happen late because
// otherwise our loop iterators won't work.
SmallPtrSet<BasicBlock *, 8> blocks;
blocks.insert(L->block_begin(), L->block_end());
for (BasicBlock *BB : blocks)
LI.removeBlock(BB);
// The last step is to update LoopInfo now that we've eliminated this loop.
LI.erase(L);
}
PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &Updater) {

122
lib/Transforms/Utils/LoopUtils.cpp
View File

@ -1137,6 +1137,128 @@ llvm::collectChildrenInLoop(DomTreeNode *N, const Loop *CurLoop) {
return Worklist;
}
void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT = nullptr,
ScalarEvolution *SE = nullptr,
LoopInfo *LI = nullptr) {
assert(!DT || L->isLCSSAForm(*DT) && "Expected LCSSA!");
auto *Preheader = L->getLoopPreheader();
assert(Preheader && "Preheader should exist!");
// Now that we know the removal is safe, remove the loop by changing the
// branch from the preheader to go to the single exit block.
//
// Because we're deleting a large chunk of code at once, the sequence in which
// we remove things is very important to avoid invalidation issues.
// Tell ScalarEvolution that the loop is deleted. Do this before
// deleting the loop so that ScalarEvolution can look at the loop
// to determine what it needs to clean up.
if (SE)
SE->forgetLoop(L);
auto *ExitBlock = L->getUniqueExitBlock();
assert(ExitBlock && "Should have a unique exit block!");
assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
auto *OldBr = dyn_cast<BranchInst>(Preheader->getTerminator());
assert(OldBr && "Preheader must end with a branch");
assert(OldBr->isUnconditional() && "Preheader must have a single successor");
// Connect the preheader to the exit block. Keep the old edge to the header
// around to perform the dominator tree update in two separate steps
// -- #1 insertion of the edge preheader -> exit and #2 deletion of the edge
// preheader -> header.
//
//
// 0. Preheader 1. Preheader 2. Preheader
// | | | |
// V | V |
// Header <--\ | Header <--\ | Header <--\
// | | | | | | | | | | |
// | V | | | V | | | V |
// | Body --/ | | Body --/ | | Body --/
// V V V V V
// Exit Exit Exit
//
// By doing this is two separate steps we can perform the dominator tree
// update without using the batch update API.
//
// Even when the loop is never executed, we cannot remove the edge from the
// source block to the exit block. Consider the case where the unexecuted loop
// branches back to an outer loop. If we deleted the loop and removed the edge
// coming to this inner loop, this will break the outer loop structure (by
// deleting the backedge of the outer loop). If the outer loop is indeed a
// non-loop, it will be deleted in a future iteration of loop deletion pass.
IRBuilder<> Builder(OldBr);
Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
// Remove the old branch. The conditional branch becomes a new terminator.
OldBr->eraseFromParent();
// Rewrite phis in the exit block to get their inputs from the Preheader
// instead of the exiting block.
BasicBlock::iterator BI = ExitBlock->begin();
while (PHINode *P = dyn_cast<PHINode>(BI)) {
// Set the zero'th element of Phi to be from the preheader and remove all
// other incoming values. Given the loop has dedicated exits, all other
// incoming values must be from the exiting blocks.
int PredIndex = 0;
P->setIncomingBlock(PredIndex, Preheader);
// Removes all incoming values from all other exiting blocks (including
// duplicate values from an exiting block).
// Nuke all entries except the zero'th entry which is the preheader entry.
// NOTE! We need to remove Incoming Values in the reverse order as done
// below, to keep the indices valid for deletion (removeIncomingValues
// updates getNumIncomingValues and shifts all values down into the operand
// being deleted).
for (unsigned i = 0, e = P->getNumIncomingValues() - 1; i != e; ++i)
P->removeIncomingValue(e - i, false);
assert((P->getNumIncomingValues() == 1 &&
P->getIncomingBlock(PredIndex) == Preheader) &&
"Should have exactly one value and that's from the preheader!");
++BI;
}
// Disconnect the loop body by branching directly to its exit.
Builder.SetInsertPoint(Preheader->getTerminator());
Builder.CreateBr(ExitBlock);
// Remove the old branch.
Preheader->getTerminator()->eraseFromParent();
if (DT) {
// Update the dominator tree by informing it about the new edge from the
// preheader to the exit.
DT->insertEdge(Preheader, ExitBlock);
// Inform the dominator tree about the removed edge.
DT->deleteEdge(Preheader, L->getHeader());
}
// Remove the block from the reference counting scheme, so that we can
// delete it freely later.
for (auto *Block : L->blocks())
Block->dropAllReferences();
if (LI) {
// Erase the instructions and the blocks without having to worry
// about ordering because we already dropped the references.
// NOTE: This iteration is safe because erasing the block does not remove
// its entry from the loop's block list. We do that in the next section.
for (Loop::block_iterator LpI = L->block_begin(), LpE = L->block_end();
LpI != LpE; ++LpI)
(*LpI)->eraseFromParent();
// Finally, the blocks from loopinfo. This has to happen late because
// otherwise our loop iterators won't work.
SmallPtrSet<BasicBlock *, 8> blocks;
blocks.insert(L->block_begin(), L->block_end());
for (BasicBlock *BB : blocks)
LI->removeBlock(BB);
// The last step is to update LoopInfo now that we've eliminated this loop.
LI->erase(L);
}
}
/// Returns true if the instruction in a loop is guaranteed to execute at least
/// once.
bool llvm::isGuaranteedToExecute(const Instruction &Inst,