[llvm] r314934 - [LoopDeletion] Move deleteDeadLoop to to LoopUtils. NFC
Davide Italiano via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 4 14:13:52 PDT 2017
Thanks. Are you planning to introduce new consumers?
On Wed, Oct 4, 2017 at 1:42 PM, Marcello Maggioni via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: mggm
> Date: Wed Oct 4 13:42:46 2017
> New Revision: 314934
>
> URL: http://llvm.org/viewvc/llvm-project?rev=314934&view=rev
> Log:
> [LoopDeletion] Move deleteDeadLoop to to LoopUtils. NFC
>
> Modified:
> llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
> llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp
> llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
>
> Modified: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h?rev=314934&r1=314933&r2=314934&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h (original)
> +++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h Wed Oct 4 13:42:46 2017
> @@ -439,6 +439,20 @@ bool hoistRegion(DomTreeNode *, AliasAna
> 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
>
> Modified: llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp?rev=314934&r1=314933&r2=314934&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp Wed Oct 4 13:42:46 2017
> @@ -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 deleteLoopIfDe
> 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 deleteLoopIfDe
> }
>
> 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) {
>
> Modified: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp?rev=314934&r1=314933&r2=314934&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp Wed Oct 4 13:42:46 2017
> @@ -1137,6 +1137,128 @@ llvm::collectChildrenInLoop(DomTreeNode
> 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,
>
>
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--
Davide
"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare
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