mirror of
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into their new header subdirectory: include/llvm/IR. This matches the directory structure of lib, and begins to correct a long standing point of file layout clutter in LLVM. There are still more header files to move here, but I wanted to handle them in separate commits to make tracking what files make sense at each layer easier. The only really questionable files here are the target intrinsic tablegen files. But that's a battle I'd rather not fight today. I've updated both CMake and Makefile build systems (I think, and my tests think, but I may have missed something). I've also re-sorted the includes throughout the project. I'll be committing updates to Clang, DragonEgg, and Polly momentarily. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171366 91177308-0d34-0410-b5e6-96231b3b80d8
458 lines
17 KiB
C++
458 lines
17 KiB
C++
//===-- UnrollLoop.cpp - Loop unrolling utilities -------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements some loop unrolling utilities. It does not define any
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// actual pass or policy, but provides a single function to perform loop
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// unrolling.
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//
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// The process of unrolling can produce extraneous basic blocks linked with
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// unconditional branches. This will be corrected in the future.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-unroll"
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#include "llvm/Transforms/Utils/UnrollLoop.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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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/SimplifyIndVar.h"
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using namespace llvm;
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// TODO: Should these be here or in LoopUnroll?
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STATISTIC(NumCompletelyUnrolled, "Number of loops completely unrolled");
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STATISTIC(NumUnrolled, "Number of loops unrolled (completely or otherwise)");
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/// RemapInstruction - Convert the instruction operands from referencing the
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/// current values into those specified by VMap.
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static inline void RemapInstruction(Instruction *I,
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ValueToValueMapTy &VMap) {
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for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
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Value *Op = I->getOperand(op);
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ValueToValueMapTy::iterator It = VMap.find(Op);
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if (It != VMap.end())
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I->setOperand(op, It->second);
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}
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if (PHINode *PN = dyn_cast<PHINode>(I)) {
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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ValueToValueMapTy::iterator It = VMap.find(PN->getIncomingBlock(i));
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if (It != VMap.end())
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PN->setIncomingBlock(i, cast<BasicBlock>(It->second));
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}
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}
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}
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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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// 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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BasicBlock *OnlyPred = BB->getSinglePredecessor();
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if (!OnlyPred) return 0;
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if (OnlyPred->getTerminator()->getNumSuccessors() != 1)
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return 0;
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DEBUG(dbgs() << "Merging: " << *BB << "into: " << *OnlyPred);
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// Resolve any PHI nodes at the start of the block. They are all
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// guaranteed to have exactly one entry if they exist, unless there are
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// multiple duplicate (but guaranteed to be equal) entries for the
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// incoming edges. This occurs when there are multiple edges from
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// OnlyPred to OnlySucc.
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FoldSingleEntryPHINodes(BB);
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// Delete the unconditional branch from the predecessor...
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OnlyPred->getInstList().pop_back();
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// Make all PHI nodes that referred to BB now refer to Pred as their
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// source...
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BB->replaceAllUsesWith(OnlyPred);
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// Move all definitions in the successor to the predecessor...
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OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
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std::string OldName = BB->getName();
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// Erase basic block from the function...
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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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}
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}
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LI->removeBlock(BB);
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BB->eraseFromParent();
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// Inherit predecessor's name if it exists...
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if (!OldName.empty() && !OnlyPred->hasName())
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OnlyPred->setName(OldName);
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return OnlyPred;
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}
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/// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
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/// if unrolling was successful, or false if the loop was unmodified. Unrolling
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/// can only fail when the loop's latch block is not terminated by a conditional
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/// branch instruction. However, if the trip count (and multiple) are not known,
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/// loop unrolling will mostly produce more code that is no faster.
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///
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/// TripCount is generally defined as the number of times the loop header
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/// executes. UnrollLoop relaxes the definition to permit early exits: here
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/// TripCount is the iteration on which control exits LatchBlock if no early
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/// exits were taken. Note that UnrollLoop assumes that the loop counter test
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/// terminates LatchBlock in order to remove unnecesssary instances of the
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/// test. In other words, control may exit the loop prior to TripCount
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/// iterations via an early branch, but control may not exit the loop from the
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/// LatchBlock's terminator prior to TripCount iterations.
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///
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/// Similarly, TripMultiple divides the number of times that the LatchBlock may
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/// execute without exiting the loop.
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///
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/// The LoopInfo Analysis that is passed will be kept consistent.
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///
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/// If a LoopPassManager is passed in, and the loop is fully removed, it will be
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/// removed from the LoopPassManager as well. LPM can also be NULL.
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///
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/// This utility preserves LoopInfo. If DominatorTree or ScalarEvolution are
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/// available it must also preserve those analyses.
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bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
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bool AllowRuntime, unsigned TripMultiple,
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LoopInfo *LI, LPPassManager *LPM) {
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BasicBlock *Preheader = L->getLoopPreheader();
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if (!Preheader) {
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DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
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return false;
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}
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BasicBlock *LatchBlock = L->getLoopLatch();
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if (!LatchBlock) {
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DEBUG(dbgs() << " Can't unroll; loop exit-block-insertion failed.\n");
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return false;
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}
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// Loops with indirectbr cannot be cloned.
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if (!L->isSafeToClone()) {
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DEBUG(dbgs() << " Can't unroll; Loop body cannot be cloned.\n");
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return false;
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}
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BasicBlock *Header = L->getHeader();
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BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->getTerminator());
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if (!BI || BI->isUnconditional()) {
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// The loop-rotate pass can be helpful to avoid this in many cases.
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DEBUG(dbgs() <<
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" Can't unroll; loop not terminated by a conditional branch.\n");
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return false;
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}
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if (Header->hasAddressTaken()) {
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// The loop-rotate pass can be helpful to avoid this in many cases.
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DEBUG(dbgs() <<
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" Won't unroll loop: address of header block is taken.\n");
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return false;
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}
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if (TripCount != 0)
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DEBUG(dbgs() << " Trip Count = " << TripCount << "\n");
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if (TripMultiple != 1)
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DEBUG(dbgs() << " Trip Multiple = " << TripMultiple << "\n");
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// Effectively "DCE" unrolled iterations that are beyond the tripcount
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// and will never be executed.
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if (TripCount != 0 && Count > TripCount)
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Count = TripCount;
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// Don't enter the unroll code if there is nothing to do. This way we don't
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// need to support "partial unrolling by 1".
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if (TripCount == 0 && Count < 2)
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return false;
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assert(Count > 0);
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assert(TripMultiple > 0);
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assert(TripCount == 0 || TripCount % TripMultiple == 0);
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// Are we eliminating the loop control altogether?
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bool CompletelyUnroll = Count == TripCount;
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// We assume a run-time trip count if the compiler cannot
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// figure out the loop trip count and the unroll-runtime
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// flag is specified.
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bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime);
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if (RuntimeTripCount && !UnrollRuntimeLoopProlog(L, Count, LI, LPM))
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return false;
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// Notify ScalarEvolution that the loop will be substantially changed,
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// if not outright eliminated.
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if (LPM) {
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ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>();
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if (SE)
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SE->forgetLoop(L);
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}
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// If we know the trip count, we know the multiple...
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unsigned BreakoutTrip = 0;
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if (TripCount != 0) {
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BreakoutTrip = TripCount % Count;
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TripMultiple = 0;
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} else {
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// Figure out what multiple to use.
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BreakoutTrip = TripMultiple =
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(unsigned)GreatestCommonDivisor64(Count, TripMultiple);
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}
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if (CompletelyUnroll) {
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DEBUG(dbgs() << "COMPLETELY UNROLLING loop %" << Header->getName()
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<< " with trip count " << TripCount << "!\n");
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} else {
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DEBUG(dbgs() << "UNROLLING loop %" << Header->getName()
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<< " by " << Count);
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if (TripMultiple == 0 || BreakoutTrip != TripMultiple) {
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DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip);
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} else if (TripMultiple != 1) {
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DEBUG(dbgs() << " with " << TripMultiple << " trips per branch");
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} else if (RuntimeTripCount) {
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DEBUG(dbgs() << " with run-time trip count");
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}
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DEBUG(dbgs() << "!\n");
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}
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std::vector<BasicBlock*> LoopBlocks = L->getBlocks();
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bool ContinueOnTrue = L->contains(BI->getSuccessor(0));
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BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue);
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// For the first iteration of the loop, we should use the precloned values for
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// PHI nodes. Insert associations now.
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ValueToValueMapTy LastValueMap;
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std::vector<PHINode*> OrigPHINode;
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for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
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OrigPHINode.push_back(cast<PHINode>(I));
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}
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std::vector<BasicBlock*> Headers;
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std::vector<BasicBlock*> Latches;
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Headers.push_back(Header);
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Latches.push_back(LatchBlock);
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// The current on-the-fly SSA update requires blocks to be processed in
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// reverse postorder so that LastValueMap contains the correct value at each
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// exit.
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LoopBlocksDFS DFS(L);
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DFS.perform(LI);
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// Stash the DFS iterators before adding blocks to the loop.
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LoopBlocksDFS::RPOIterator BlockBegin = DFS.beginRPO();
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LoopBlocksDFS::RPOIterator BlockEnd = DFS.endRPO();
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for (unsigned It = 1; It != Count; ++It) {
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std::vector<BasicBlock*> NewBlocks;
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for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
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ValueToValueMapTy VMap;
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BasicBlock *New = CloneBasicBlock(*BB, VMap, "." + Twine(It));
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Header->getParent()->getBasicBlockList().push_back(New);
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// Loop over all of the PHI nodes in the block, changing them to use the
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// incoming values from the previous block.
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if (*BB == Header)
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for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
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PHINode *NewPHI = cast<PHINode>(VMap[OrigPHINode[i]]);
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Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock);
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if (Instruction *InValI = dyn_cast<Instruction>(InVal))
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if (It > 1 && L->contains(InValI))
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InVal = LastValueMap[InValI];
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VMap[OrigPHINode[i]] = InVal;
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New->getInstList().erase(NewPHI);
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}
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// Update our running map of newest clones
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LastValueMap[*BB] = New;
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for (ValueToValueMapTy::iterator VI = VMap.begin(), VE = VMap.end();
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VI != VE; ++VI)
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LastValueMap[VI->first] = VI->second;
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L->addBasicBlockToLoop(New, LI->getBase());
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// Add phi entries for newly created values to all exit blocks.
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for (succ_iterator SI = succ_begin(*BB), SE = succ_end(*BB);
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SI != SE; ++SI) {
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if (L->contains(*SI))
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continue;
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *phi = dyn_cast<PHINode>(BBI); ++BBI) {
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Value *Incoming = phi->getIncomingValueForBlock(*BB);
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ValueToValueMapTy::iterator It = LastValueMap.find(Incoming);
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if (It != LastValueMap.end())
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Incoming = It->second;
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phi->addIncoming(Incoming, New);
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}
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}
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// Keep track of new headers and latches as we create them, so that
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// we can insert the proper branches later.
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if (*BB == Header)
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Headers.push_back(New);
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if (*BB == LatchBlock)
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Latches.push_back(New);
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NewBlocks.push_back(New);
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}
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// Remap all instructions in the most recent iteration
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for (unsigned i = 0; i < NewBlocks.size(); ++i)
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for (BasicBlock::iterator I = NewBlocks[i]->begin(),
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E = NewBlocks[i]->end(); I != E; ++I)
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::RemapInstruction(I, LastValueMap);
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}
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// Loop over the PHI nodes in the original block, setting incoming values.
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for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
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PHINode *PN = OrigPHINode[i];
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if (CompletelyUnroll) {
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PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
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Header->getInstList().erase(PN);
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}
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else if (Count > 1) {
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Value *InVal = PN->removeIncomingValue(LatchBlock, false);
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// If this value was defined in the loop, take the value defined by the
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// last iteration of the loop.
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if (Instruction *InValI = dyn_cast<Instruction>(InVal)) {
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if (L->contains(InValI))
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InVal = LastValueMap[InVal];
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}
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assert(Latches.back() == LastValueMap[LatchBlock] && "bad last latch");
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PN->addIncoming(InVal, Latches.back());
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}
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}
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// Now that all the basic blocks for the unrolled iterations are in place,
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// set up the branches to connect them.
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for (unsigned i = 0, e = Latches.size(); i != e; ++i) {
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// The original branch was replicated in each unrolled iteration.
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BranchInst *Term = cast<BranchInst>(Latches[i]->getTerminator());
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// The branch destination.
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unsigned j = (i + 1) % e;
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BasicBlock *Dest = Headers[j];
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bool NeedConditional = true;
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if (RuntimeTripCount && j != 0) {
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NeedConditional = false;
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}
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// For a complete unroll, make the last iteration end with a branch
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// to the exit block.
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if (CompletelyUnroll && j == 0) {
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Dest = LoopExit;
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NeedConditional = false;
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}
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// If we know the trip count or a multiple of it, we can safely use an
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// unconditional branch for some iterations.
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if (j != BreakoutTrip && (TripMultiple == 0 || j % TripMultiple != 0)) {
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NeedConditional = false;
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}
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if (NeedConditional) {
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// Update the conditional branch's successor for the following
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// iteration.
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Term->setSuccessor(!ContinueOnTrue, Dest);
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} else {
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// Remove phi operands at this loop exit
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if (Dest != LoopExit) {
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BasicBlock *BB = Latches[i];
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
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SI != SE; ++SI) {
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if (*SI == Headers[i])
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continue;
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for (BasicBlock::iterator BBI = (*SI)->begin();
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PHINode *Phi = dyn_cast<PHINode>(BBI); ++BBI) {
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Phi->removeIncomingValue(BB, false);
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}
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}
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}
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// Replace the conditional branch with an unconditional one.
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BranchInst::Create(Dest, Term);
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Term->eraseFromParent();
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}
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}
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// Merge adjacent basic blocks, if possible.
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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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std::replace(Latches.begin(), Latches.end(), Dest, Fold);
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}
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}
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if (LPM) {
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// FIXME: Reconstruct dom info, because it is not preserved properly.
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// Incrementally updating domtree after loop unrolling would be easy.
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if (DominatorTree *DT = LPM->getAnalysisIfAvailable<DominatorTree>())
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DT->runOnFunction(*L->getHeader()->getParent());
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// Simplify any new induction variables in the partially unrolled loop.
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ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>();
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if (SE && !CompletelyUnroll) {
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SmallVector<WeakVH, 16> DeadInsts;
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simplifyLoopIVs(L, SE, LPM, DeadInsts);
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// Aggressively clean up dead instructions that simplifyLoopIVs already
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// identified. Any remaining should be cleaned up below.
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while (!DeadInsts.empty())
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if (Instruction *Inst =
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dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
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RecursivelyDeleteTriviallyDeadInstructions(Inst);
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}
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}
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// At this point, the code is well formed. We now do a quick sweep over the
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// inserted code, doing constant propagation and dead code elimination as we
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// go.
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const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks();
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for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(),
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BBE = NewLoopBlocks.end(); BB != BBE; ++BB)
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for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ) {
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Instruction *Inst = I++;
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if (isInstructionTriviallyDead(Inst))
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(*BB)->getInstList().erase(Inst);
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else if (Value *V = SimplifyInstruction(Inst))
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if (LI->replacementPreservesLCSSAForm(Inst, V)) {
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Inst->replaceAllUsesWith(V);
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(*BB)->getInstList().erase(Inst);
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}
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}
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NumCompletelyUnrolled += CompletelyUnroll;
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++NumUnrolled;
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// Remove the loop from the LoopPassManager if it's completely removed.
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|
if (CompletelyUnroll && LPM != NULL)
|
|
LPM->deleteLoopFromQueue(L);
|
|
|
|
return true;
|
|
}
|