mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-29 13:29:28 +00:00
function and a FunctionPass. This has many benefits. The motivating use case was to be able to compute function analysis passes *after* running LoopSimplify (to avoid invalidating them) and then to run other passes which require LoopSimplify. Specifically passes like unrolling and vectorization are critical to wire up to BranchProbabilityInfo and BlockFrequencyInfo so that they can be profile aware. For the LoopVectorize pass the only things in the way are LoopSimplify and LCSSA. This fixes LoopSimplify and LCSSA is next on my list. There are also a bunch of other benefits of doing this: - It is now very feasible to make more passes *preserve* LoopSimplify because they can simply run it after changing a loop. Because subsequence passes can assume LoopSimplify is preserved we can reduce the runs of this pass to the times when we actually mutate a loop structure. - The new pass manager should be able to more easily support loop passes factored in this way. - We can at long, long last observe that LoopSimplify is preserved across SCEV. This *halves* the number of times we run LoopSimplify!!! Now, getting here wasn't trivial. First off, the interfaces used by LoopSimplify are all over the map regarding how analysis are updated. We end up with weird "pass" parameters as a consequence. I'll try to clean at least some of this up later -- I'll have to have it all clean for the new pass manager. Next up I discovered a really frustrating bug. LoopUnroll *claims* to preserve LoopSimplify. That's actually a lie. But the way the LoopPassManager ends up running the passes, it always ran LoopSimplify on the unrolled-into loop, rectifying this oversight before any verification could kick in and point out that in fact nothing was preserved. So I've added code to the unroller to *actually* simplify the surrounding loop when it succeeds at unrolling. The only functional change in the test suite is that we now catch a case that was previously missed because SCEV and other loop transforms see their containing loops as simplified and thus don't miss some opportunities. One test case has been converted to check that we catch this case rather than checking that we miss it but at least don't get the wrong answer. Note that I have #if-ed out all of the verification logic in LoopSimplify! This is a temporary workaround while extracting these bits from the LoopPassManager. Currently, there is no way to have a pass in the LoopPassManager which preserves LoopSimplify along with one which does not. The LPM will try to verify on each loop in the nest that LoopSimplify holds but the now-Function-pass cannot distinguish what loop is being verified and so must try to verify all of them. The inner most loop is clearly no longer simplified as there is a pass which didn't even *attempt* to preserve it. =/ Once I get LCSSA out (and maybe LoopVectorize and some other fixes) I'll be able to re-enable this check and catch any places where we are still failing to preserve LoopSimplify. If this causes problems I can back this out and try to commit *all* of this at once, but so far this seems to work and allow much more incremental progress. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199884 91177308-0d34-0410-b5e6-96231b3b80d8
858 lines
32 KiB
C++
858 lines
32 KiB
C++
//===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass performs several transformations to transform natural loops into a
|
|
// simpler form, which makes subsequent analyses and transformations simpler and
|
|
// more effective.
|
|
//
|
|
// Loop pre-header insertion guarantees that there is a single, non-critical
|
|
// entry edge from outside of the loop to the loop header. This simplifies a
|
|
// number of analyses and transformations, such as LICM.
|
|
//
|
|
// Loop exit-block insertion guarantees that all exit blocks from the loop
|
|
// (blocks which are outside of the loop that have predecessors inside of the
|
|
// loop) only have predecessors from inside of the loop (and are thus dominated
|
|
// by the loop header). This simplifies transformations such as store-sinking
|
|
// that are built into LICM.
|
|
//
|
|
// This pass also guarantees that loops will have exactly one backedge.
|
|
//
|
|
// Indirectbr instructions introduce several complications. If the loop
|
|
// contains or is entered by an indirectbr instruction, it may not be possible
|
|
// to transform the loop and make these guarantees. Client code should check
|
|
// that these conditions are true before relying on them.
|
|
//
|
|
// Note that the simplifycfg pass will clean up blocks which are split out but
|
|
// end up being unnecessary, so usage of this pass should not pessimize
|
|
// generated code.
|
|
//
|
|
// This pass obviously modifies the CFG, but updates loop information and
|
|
// dominator information.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#define DEBUG_TYPE "loop-simplify"
|
|
#include "llvm/Transforms/Scalar.h"
|
|
#include "llvm/ADT/DepthFirstIterator.h"
|
|
#include "llvm/ADT/SetOperations.h"
|
|
#include "llvm/ADT/SetVector.h"
|
|
#include "llvm/ADT/SmallVector.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Analysis/DependenceAnalysis.h"
|
|
#include "llvm/Analysis/InstructionSimplify.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/ScalarEvolution.h"
|
|
#include "llvm/IR/Constants.h"
|
|
#include "llvm/IR/Dominators.h"
|
|
#include "llvm/IR/Function.h"
|
|
#include "llvm/IR/Instructions.h"
|
|
#include "llvm/IR/IntrinsicInst.h"
|
|
#include "llvm/IR/LLVMContext.h"
|
|
#include "llvm/IR/Type.h"
|
|
#include "llvm/Support/CFG.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Transforms/Utils/LoopUtils.h"
|
|
using namespace llvm;
|
|
|
|
STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
|
|
STATISTIC(NumNested , "Number of nested loops split out");
|
|
|
|
// If the block isn't already, move the new block to right after some 'outside
|
|
// block' block. This prevents the preheader from being placed inside the loop
|
|
// body, e.g. when the loop hasn't been rotated.
|
|
static void placeSplitBlockCarefully(BasicBlock *NewBB,
|
|
SmallVectorImpl<BasicBlock *> &SplitPreds,
|
|
Loop *L) {
|
|
// Check to see if NewBB is already well placed.
|
|
Function::iterator BBI = NewBB; --BBI;
|
|
for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
|
|
if (&*BBI == SplitPreds[i])
|
|
return;
|
|
}
|
|
|
|
// If it isn't already after an outside block, move it after one. This is
|
|
// always good as it makes the uncond branch from the outside block into a
|
|
// fall-through.
|
|
|
|
// Figure out *which* outside block to put this after. Prefer an outside
|
|
// block that neighbors a BB actually in the loop.
|
|
BasicBlock *FoundBB = 0;
|
|
for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
|
|
Function::iterator BBI = SplitPreds[i];
|
|
if (++BBI != NewBB->getParent()->end() &&
|
|
L->contains(BBI)) {
|
|
FoundBB = SplitPreds[i];
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If our heuristic for a *good* bb to place this after doesn't find
|
|
// anything, just pick something. It's likely better than leaving it within
|
|
// the loop.
|
|
if (!FoundBB)
|
|
FoundBB = SplitPreds[0];
|
|
NewBB->moveAfter(FoundBB);
|
|
}
|
|
|
|
/// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
|
|
/// preheader, this method is called to insert one. This method has two phases:
|
|
/// preheader insertion and analysis updating.
|
|
///
|
|
BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) {
|
|
BasicBlock *Header = L->getHeader();
|
|
|
|
// Compute the set of predecessors of the loop that are not in the loop.
|
|
SmallVector<BasicBlock*, 8> OutsideBlocks;
|
|
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
|
|
PI != PE; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
if (!L->contains(P)) { // Coming in from outside the loop?
|
|
// If the loop is branched to from an indirect branch, we won't
|
|
// be able to fully transform the loop, because it prohibits
|
|
// edge splitting.
|
|
if (isa<IndirectBrInst>(P->getTerminator())) return 0;
|
|
|
|
// Keep track of it.
|
|
OutsideBlocks.push_back(P);
|
|
}
|
|
}
|
|
|
|
// Split out the loop pre-header.
|
|
BasicBlock *PreheaderBB;
|
|
if (!Header->isLandingPad()) {
|
|
PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader",
|
|
PP);
|
|
} else {
|
|
SmallVector<BasicBlock*, 2> NewBBs;
|
|
SplitLandingPadPredecessors(Header, OutsideBlocks, ".preheader",
|
|
".split-lp", PP, NewBBs);
|
|
PreheaderBB = NewBBs[0];
|
|
}
|
|
|
|
PreheaderBB->getTerminator()->setDebugLoc(
|
|
Header->getFirstNonPHI()->getDebugLoc());
|
|
DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
|
|
<< PreheaderBB->getName() << "\n");
|
|
|
|
// Make sure that NewBB is put someplace intelligent, which doesn't mess up
|
|
// code layout too horribly.
|
|
placeSplitBlockCarefully(PreheaderBB, OutsideBlocks, L);
|
|
|
|
return PreheaderBB;
|
|
}
|
|
|
|
/// \brief Ensure that the loop preheader dominates all exit blocks.
|
|
///
|
|
/// This method is used to split exit blocks that have predecessors outside of
|
|
/// the loop.
|
|
static BasicBlock *rewriteLoopExitBlock(Loop *L, BasicBlock *Exit, Pass *PP) {
|
|
SmallVector<BasicBlock*, 8> LoopBlocks;
|
|
for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) {
|
|
BasicBlock *P = *I;
|
|
if (L->contains(P)) {
|
|
// Don't do this if the loop is exited via an indirect branch.
|
|
if (isa<IndirectBrInst>(P->getTerminator())) return 0;
|
|
|
|
LoopBlocks.push_back(P);
|
|
}
|
|
}
|
|
|
|
assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
|
|
BasicBlock *NewExitBB = 0;
|
|
|
|
if (Exit->isLandingPad()) {
|
|
SmallVector<BasicBlock*, 2> NewBBs;
|
|
SplitLandingPadPredecessors(Exit, ArrayRef<BasicBlock*>(&LoopBlocks[0],
|
|
LoopBlocks.size()),
|
|
".loopexit", ".nonloopexit",
|
|
PP, NewBBs);
|
|
NewExitBB = NewBBs[0];
|
|
} else {
|
|
NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", PP);
|
|
}
|
|
|
|
DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
|
|
<< NewExitBB->getName() << "\n");
|
|
return NewExitBB;
|
|
}
|
|
|
|
/// Add the specified block, and all of its predecessors, to the specified set,
|
|
/// if it's not already in there. Stop predecessor traversal when we reach
|
|
/// StopBlock.
|
|
static void addBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
|
|
std::set<BasicBlock*> &Blocks) {
|
|
SmallVector<BasicBlock *, 8> Worklist;
|
|
Worklist.push_back(InputBB);
|
|
do {
|
|
BasicBlock *BB = Worklist.pop_back_val();
|
|
if (Blocks.insert(BB).second && BB != StopBlock)
|
|
// If BB is not already processed and it is not a stop block then
|
|
// insert its predecessor in the work list
|
|
for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
|
|
BasicBlock *WBB = *I;
|
|
Worklist.push_back(WBB);
|
|
}
|
|
} while (!Worklist.empty());
|
|
}
|
|
|
|
/// \brief The first part of loop-nestification is to find a PHI node that tells
|
|
/// us how to partition the loops.
|
|
static PHINode *findPHIToPartitionLoops(Loop *L, AliasAnalysis *AA,
|
|
DominatorTree *DT) {
|
|
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
++I;
|
|
if (Value *V = SimplifyInstruction(PN, 0, 0, DT)) {
|
|
// This is a degenerate PHI already, don't modify it!
|
|
PN->replaceAllUsesWith(V);
|
|
if (AA) AA->deleteValue(PN);
|
|
PN->eraseFromParent();
|
|
continue;
|
|
}
|
|
|
|
// Scan this PHI node looking for a use of the PHI node by itself.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingValue(i) == PN &&
|
|
L->contains(PN->getIncomingBlock(i)))
|
|
// We found something tasty to remove.
|
|
return PN;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/// \brief If this loop has multiple backedges, try to pull one of them out into
|
|
/// a nested loop.
|
|
///
|
|
/// This is important for code that looks like
|
|
/// this:
|
|
///
|
|
/// Loop:
|
|
/// ...
|
|
/// br cond, Loop, Next
|
|
/// ...
|
|
/// br cond2, Loop, Out
|
|
///
|
|
/// To identify this common case, we look at the PHI nodes in the header of the
|
|
/// loop. PHI nodes with unchanging values on one backedge correspond to values
|
|
/// that change in the "outer" loop, but not in the "inner" loop.
|
|
///
|
|
/// If we are able to separate out a loop, return the new outer loop that was
|
|
/// created.
|
|
///
|
|
static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
|
|
AliasAnalysis *AA, DominatorTree *DT,
|
|
LoopInfo *LI, ScalarEvolution *SE, Pass *PP) {
|
|
// Don't try to separate loops without a preheader.
|
|
if (!Preheader)
|
|
return 0;
|
|
|
|
// The header is not a landing pad; preheader insertion should ensure this.
|
|
assert(!L->getHeader()->isLandingPad() &&
|
|
"Can't insert backedge to landing pad");
|
|
|
|
PHINode *PN = findPHIToPartitionLoops(L, AA, DT);
|
|
if (PN == 0) return 0; // No known way to partition.
|
|
|
|
// Pull out all predecessors that have varying values in the loop. This
|
|
// handles the case when a PHI node has multiple instances of itself as
|
|
// arguments.
|
|
SmallVector<BasicBlock*, 8> OuterLoopPreds;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
if (PN->getIncomingValue(i) != PN ||
|
|
!L->contains(PN->getIncomingBlock(i))) {
|
|
// We can't split indirectbr edges.
|
|
if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
|
|
return 0;
|
|
OuterLoopPreds.push_back(PN->getIncomingBlock(i));
|
|
}
|
|
}
|
|
DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
|
|
|
|
// If ScalarEvolution is around and knows anything about values in
|
|
// this loop, tell it to forget them, because we're about to
|
|
// substantially change it.
|
|
if (SE)
|
|
SE->forgetLoop(L);
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *NewBB =
|
|
SplitBlockPredecessors(Header, OuterLoopPreds, ".outer", PP);
|
|
|
|
// Make sure that NewBB is put someplace intelligent, which doesn't mess up
|
|
// code layout too horribly.
|
|
placeSplitBlockCarefully(NewBB, OuterLoopPreds, L);
|
|
|
|
// Create the new outer loop.
|
|
Loop *NewOuter = new Loop();
|
|
|
|
// Change the parent loop to use the outer loop as its child now.
|
|
if (Loop *Parent = L->getParentLoop())
|
|
Parent->replaceChildLoopWith(L, NewOuter);
|
|
else
|
|
LI->changeTopLevelLoop(L, NewOuter);
|
|
|
|
// L is now a subloop of our outer loop.
|
|
NewOuter->addChildLoop(L);
|
|
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
NewOuter->addBlockEntry(*I);
|
|
|
|
// Now reset the header in L, which had been moved by
|
|
// SplitBlockPredecessors for the outer loop.
|
|
L->moveToHeader(Header);
|
|
|
|
// Determine which blocks should stay in L and which should be moved out to
|
|
// the Outer loop now.
|
|
std::set<BasicBlock*> BlocksInL;
|
|
for (pred_iterator PI=pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
if (DT->dominates(Header, P))
|
|
addBlockAndPredsToSet(P, Header, BlocksInL);
|
|
}
|
|
|
|
// Scan all of the loop children of L, moving them to OuterLoop if they are
|
|
// not part of the inner loop.
|
|
const std::vector<Loop*> &SubLoops = L->getSubLoops();
|
|
for (size_t I = 0; I != SubLoops.size(); )
|
|
if (BlocksInL.count(SubLoops[I]->getHeader()))
|
|
++I; // Loop remains in L
|
|
else
|
|
NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
|
|
|
|
// Now that we know which blocks are in L and which need to be moved to
|
|
// OuterLoop, move any blocks that need it.
|
|
for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
|
|
BasicBlock *BB = L->getBlocks()[i];
|
|
if (!BlocksInL.count(BB)) {
|
|
// Move this block to the parent, updating the exit blocks sets
|
|
L->removeBlockFromLoop(BB);
|
|
if ((*LI)[BB] == L)
|
|
LI->changeLoopFor(BB, NewOuter);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
return NewOuter;
|
|
}
|
|
|
|
/// \brief This method is called when the specified loop has more than one
|
|
/// backedge in it.
|
|
///
|
|
/// If this occurs, revector all of these backedges to target a new basic block
|
|
/// and have that block branch to the loop header. This ensures that loops
|
|
/// have exactly one backedge.
|
|
static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
|
|
AliasAnalysis *AA,
|
|
DominatorTree *DT, LoopInfo *LI) {
|
|
assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
|
|
|
|
// Get information about the loop
|
|
BasicBlock *Header = L->getHeader();
|
|
Function *F = Header->getParent();
|
|
|
|
// Unique backedge insertion currently depends on having a preheader.
|
|
if (!Preheader)
|
|
return 0;
|
|
|
|
// The header is not a landing pad; preheader insertion should ensure this.
|
|
assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
|
|
|
|
// Figure out which basic blocks contain back-edges to the loop header.
|
|
std::vector<BasicBlock*> BackedgeBlocks;
|
|
for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I){
|
|
BasicBlock *P = *I;
|
|
|
|
// Indirectbr edges cannot be split, so we must fail if we find one.
|
|
if (isa<IndirectBrInst>(P->getTerminator()))
|
|
return 0;
|
|
|
|
if (P != Preheader) BackedgeBlocks.push_back(P);
|
|
}
|
|
|
|
// Create and insert the new backedge block...
|
|
BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
|
|
Header->getName()+".backedge", F);
|
|
BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
|
|
|
|
DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block "
|
|
<< BEBlock->getName() << "\n");
|
|
|
|
// Move the new backedge block to right after the last backedge block.
|
|
Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
|
|
F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
|
|
|
|
// Now that the block has been inserted into the function, create PHI nodes in
|
|
// the backedge block which correspond to any PHI nodes in the header block.
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
PHINode *NewPN = PHINode::Create(PN->getType(), BackedgeBlocks.size(),
|
|
PN->getName()+".be", BETerminator);
|
|
if (AA) AA->copyValue(PN, NewPN);
|
|
|
|
// Loop over the PHI node, moving all entries except the one for the
|
|
// preheader over to the new PHI node.
|
|
unsigned PreheaderIdx = ~0U;
|
|
bool HasUniqueIncomingValue = true;
|
|
Value *UniqueValue = 0;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *IBB = PN->getIncomingBlock(i);
|
|
Value *IV = PN->getIncomingValue(i);
|
|
if (IBB == Preheader) {
|
|
PreheaderIdx = i;
|
|
} else {
|
|
NewPN->addIncoming(IV, IBB);
|
|
if (HasUniqueIncomingValue) {
|
|
if (UniqueValue == 0)
|
|
UniqueValue = IV;
|
|
else if (UniqueValue != IV)
|
|
HasUniqueIncomingValue = false;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Delete all of the incoming values from the old PN except the preheader's
|
|
assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
|
|
if (PreheaderIdx != 0) {
|
|
PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
|
|
PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
|
|
}
|
|
// Nuke all entries except the zero'th.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
|
|
PN->removeIncomingValue(e-i, false);
|
|
|
|
// Finally, add the newly constructed PHI node as the entry for the BEBlock.
|
|
PN->addIncoming(NewPN, BEBlock);
|
|
|
|
// As an optimization, if all incoming values in the new PhiNode (which is a
|
|
// subset of the incoming values of the old PHI node) have the same value,
|
|
// eliminate the PHI Node.
|
|
if (HasUniqueIncomingValue) {
|
|
NewPN->replaceAllUsesWith(UniqueValue);
|
|
if (AA) AA->deleteValue(NewPN);
|
|
BEBlock->getInstList().erase(NewPN);
|
|
}
|
|
}
|
|
|
|
// Now that all of the PHI nodes have been inserted and adjusted, modify the
|
|
// backedge blocks to just to the BEBlock instead of the header.
|
|
for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
|
|
TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
|
|
for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
|
|
if (TI->getSuccessor(Op) == Header)
|
|
TI->setSuccessor(Op, BEBlock);
|
|
}
|
|
|
|
//===--- Update all analyses which we must preserve now -----------------===//
|
|
|
|
// Update Loop Information - we know that this block is now in the current
|
|
// loop and all parent loops.
|
|
L->addBasicBlockToLoop(BEBlock, LI->getBase());
|
|
|
|
// Update dominator information
|
|
DT->splitBlock(BEBlock);
|
|
|
|
return BEBlock;
|
|
}
|
|
|
|
/// \brief Simplify one loop and queue further loops for simplification.
|
|
///
|
|
/// FIXME: Currently this accepts both lots of analyses that it uses and a raw
|
|
/// Pass pointer. The Pass pointer is used by numerous utilities to update
|
|
/// specific analyses. Rather than a pass it would be much cleaner and more
|
|
/// explicit if they accepted the analysis directly and then updated it.
|
|
static bool simplifyOneLoop(Loop *L, SmallVectorImpl<Loop *> &Worklist,
|
|
AliasAnalysis *AA, DominatorTree *DT, LoopInfo *LI,
|
|
ScalarEvolution *SE, Pass *PP) {
|
|
bool Changed = false;
|
|
ReprocessLoop:
|
|
|
|
// Check to see that no blocks (other than the header) in this loop have
|
|
// predecessors that are not in the loop. This is not valid for natural
|
|
// loops, but can occur if the blocks are unreachable. Since they are
|
|
// unreachable we can just shamelessly delete those CFG edges!
|
|
for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
|
|
BB != E; ++BB) {
|
|
if (*BB == L->getHeader()) continue;
|
|
|
|
SmallPtrSet<BasicBlock*, 4> BadPreds;
|
|
for (pred_iterator PI = pred_begin(*BB),
|
|
PE = pred_end(*BB); PI != PE; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
if (!L->contains(P))
|
|
BadPreds.insert(P);
|
|
}
|
|
|
|
// Delete each unique out-of-loop (and thus dead) predecessor.
|
|
for (SmallPtrSet<BasicBlock*, 4>::iterator I = BadPreds.begin(),
|
|
E = BadPreds.end(); I != E; ++I) {
|
|
|
|
DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor "
|
|
<< (*I)->getName() << "\n");
|
|
|
|
// Inform each successor of each dead pred.
|
|
for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
|
|
(*SI)->removePredecessor(*I);
|
|
// Zap the dead pred's terminator and replace it with unreachable.
|
|
TerminatorInst *TI = (*I)->getTerminator();
|
|
TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
|
|
(*I)->getTerminator()->eraseFromParent();
|
|
new UnreachableInst((*I)->getContext(), *I);
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// If there are exiting blocks with branches on undef, resolve the undef in
|
|
// the direction which will exit the loop. This will help simplify loop
|
|
// trip count computations.
|
|
SmallVector<BasicBlock*, 8> ExitingBlocks;
|
|
L->getExitingBlocks(ExitingBlocks);
|
|
for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
|
|
E = ExitingBlocks.end(); I != E; ++I)
|
|
if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator()))
|
|
if (BI->isConditional()) {
|
|
if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {
|
|
|
|
DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in "
|
|
<< (*I)->getName() << "\n");
|
|
|
|
BI->setCondition(ConstantInt::get(Cond->getType(),
|
|
!L->contains(BI->getSuccessor(0))));
|
|
|
|
// This may make the loop analyzable, force SCEV recomputation.
|
|
if (SE)
|
|
SE->forgetLoop(L);
|
|
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// Does the loop already have a preheader? If so, don't insert one.
|
|
BasicBlock *Preheader = L->getLoopPreheader();
|
|
if (!Preheader) {
|
|
Preheader = InsertPreheaderForLoop(L, PP);
|
|
if (Preheader) {
|
|
++NumInserted;
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// Next, check to make sure that all exit nodes of the loop only have
|
|
// predecessors that are inside of the loop. This check guarantees that the
|
|
// loop preheader/header will dominate the exit blocks. If the exit block has
|
|
// predecessors from outside of the loop, split the edge now.
|
|
SmallVector<BasicBlock*, 8> ExitBlocks;
|
|
L->getExitBlocks(ExitBlocks);
|
|
|
|
SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
|
|
ExitBlocks.end());
|
|
for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
|
|
E = ExitBlockSet.end(); I != E; ++I) {
|
|
BasicBlock *ExitBlock = *I;
|
|
for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
|
|
PI != PE; ++PI)
|
|
// Must be exactly this loop: no subloops, parent loops, or non-loop preds
|
|
// allowed.
|
|
if (!L->contains(*PI)) {
|
|
if (rewriteLoopExitBlock(L, ExitBlock, PP)) {
|
|
++NumInserted;
|
|
Changed = true;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
// If the header has more than two predecessors at this point (from the
|
|
// preheader and from multiple backedges), we must adjust the loop.
|
|
BasicBlock *LoopLatch = L->getLoopLatch();
|
|
if (!LoopLatch) {
|
|
// If this is really a nested loop, rip it out into a child loop. Don't do
|
|
// this for loops with a giant number of backedges, just factor them into a
|
|
// common backedge instead.
|
|
if (L->getNumBackEdges() < 8) {
|
|
if (Loop *OuterL = separateNestedLoop(L, Preheader, AA, DT, LI, SE, PP)) {
|
|
++NumNested;
|
|
// Enqueue the outer loop as it should be processed next in our
|
|
// depth-first nest walk.
|
|
Worklist.push_back(OuterL);
|
|
|
|
// This is a big restructuring change, reprocess the whole loop.
|
|
Changed = true;
|
|
// GCC doesn't tail recursion eliminate this.
|
|
// FIXME: It isn't clear we can't rely on LLVM to TRE this.
|
|
goto ReprocessLoop;
|
|
}
|
|
}
|
|
|
|
// If we either couldn't, or didn't want to, identify nesting of the loops,
|
|
// insert a new block that all backedges target, then make it jump to the
|
|
// loop header.
|
|
LoopLatch = insertUniqueBackedgeBlock(L, Preheader, AA, DT, LI);
|
|
if (LoopLatch) {
|
|
++NumInserted;
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// Scan over the PHI nodes in the loop header. Since they now have only two
|
|
// incoming values (the loop is canonicalized), we may have simplified the PHI
|
|
// down to 'X = phi [X, Y]', which should be replaced with 'Y'.
|
|
PHINode *PN;
|
|
for (BasicBlock::iterator I = L->getHeader()->begin();
|
|
(PN = dyn_cast<PHINode>(I++)); )
|
|
if (Value *V = SimplifyInstruction(PN, 0, 0, DT)) {
|
|
if (AA) AA->deleteValue(PN);
|
|
if (SE) SE->forgetValue(PN);
|
|
PN->replaceAllUsesWith(V);
|
|
PN->eraseFromParent();
|
|
}
|
|
|
|
// If this loop has multiple exits and the exits all go to the same
|
|
// block, attempt to merge the exits. This helps several passes, such
|
|
// as LoopRotation, which do not support loops with multiple exits.
|
|
// SimplifyCFG also does this (and this code uses the same utility
|
|
// function), however this code is loop-aware, where SimplifyCFG is
|
|
// not. That gives it the advantage of being able to hoist
|
|
// loop-invariant instructions out of the way to open up more
|
|
// opportunities, and the disadvantage of having the responsibility
|
|
// to preserve dominator information.
|
|
bool UniqueExit = true;
|
|
if (!ExitBlocks.empty())
|
|
for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
|
|
if (ExitBlocks[i] != ExitBlocks[0]) {
|
|
UniqueExit = false;
|
|
break;
|
|
}
|
|
if (UniqueExit) {
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
|
|
BasicBlock *ExitingBlock = ExitingBlocks[i];
|
|
if (!ExitingBlock->getSinglePredecessor()) continue;
|
|
BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
|
|
if (!BI || !BI->isConditional()) continue;
|
|
CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
|
|
if (!CI || CI->getParent() != ExitingBlock) continue;
|
|
|
|
// Attempt to hoist out all instructions except for the
|
|
// comparison and the branch.
|
|
bool AllInvariant = true;
|
|
bool AnyInvariant = false;
|
|
for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
|
|
Instruction *Inst = I++;
|
|
// Skip debug info intrinsics.
|
|
if (isa<DbgInfoIntrinsic>(Inst))
|
|
continue;
|
|
if (Inst == CI)
|
|
continue;
|
|
if (!L->makeLoopInvariant(Inst, AnyInvariant,
|
|
Preheader ? Preheader->getTerminator() : 0)) {
|
|
AllInvariant = false;
|
|
break;
|
|
}
|
|
}
|
|
if (AnyInvariant) {
|
|
Changed = true;
|
|
// The loop disposition of all SCEV expressions that depend on any
|
|
// hoisted values have also changed.
|
|
if (SE)
|
|
SE->forgetLoopDispositions(L);
|
|
}
|
|
if (!AllInvariant) continue;
|
|
|
|
// The block has now been cleared of all instructions except for
|
|
// a comparison and a conditional branch. SimplifyCFG may be able
|
|
// to fold it now.
|
|
if (!FoldBranchToCommonDest(BI)) continue;
|
|
|
|
// Success. The block is now dead, so remove it from the loop,
|
|
// update the dominator tree and delete it.
|
|
DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block "
|
|
<< ExitingBlock->getName() << "\n");
|
|
|
|
// Notify ScalarEvolution before deleting this block. Currently assume the
|
|
// parent loop doesn't change (spliting edges doesn't count). If blocks,
|
|
// CFG edges, or other values in the parent loop change, then we need call
|
|
// to forgetLoop() for the parent instead.
|
|
if (SE)
|
|
SE->forgetLoop(L);
|
|
|
|
assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
|
|
Changed = true;
|
|
LI->removeBlock(ExitingBlock);
|
|
|
|
DomTreeNode *Node = DT->getNode(ExitingBlock);
|
|
const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
|
|
Node->getChildren();
|
|
while (!Children.empty()) {
|
|
DomTreeNode *Child = Children.front();
|
|
DT->changeImmediateDominator(Child, Node->getIDom());
|
|
}
|
|
DT->eraseNode(ExitingBlock);
|
|
|
|
BI->getSuccessor(0)->removePredecessor(ExitingBlock);
|
|
BI->getSuccessor(1)->removePredecessor(ExitingBlock);
|
|
ExitingBlock->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool llvm::simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
|
|
AliasAnalysis *AA, ScalarEvolution *SE) {
|
|
bool Changed = false;
|
|
|
|
// Worklist maintains our depth-first queue of loops in this nest to process.
|
|
SmallVector<Loop *, 4> Worklist;
|
|
Worklist.push_back(L);
|
|
|
|
// Walk the worklist from front to back, pushing newly found sub loops onto
|
|
// the back. This will let us process loops from back to front in depth-first
|
|
// order. We can use this simple process because loops form a tree.
|
|
for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
|
|
Loop *L2 = Worklist[Idx];
|
|
for (Loop::iterator I = L2->begin(), E = L2->end(); I != E; ++I)
|
|
Worklist.push_back(*I);
|
|
}
|
|
|
|
while (!Worklist.empty())
|
|
Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, AA, DT, LI, SE, PP);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
namespace {
|
|
struct LoopSimplify : public FunctionPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
LoopSimplify() : FunctionPass(ID) {
|
|
initializeLoopSimplifyPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
// AA - If we have an alias analysis object to update, this is it, otherwise
|
|
// this is null.
|
|
AliasAnalysis *AA;
|
|
DominatorTree *DT;
|
|
LoopInfo *LI;
|
|
ScalarEvolution *SE;
|
|
|
|
virtual bool runOnFunction(Function &F);
|
|
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
|
|
// We need loop information to identify the loops...
|
|
AU.addRequired<DominatorTreeWrapperPass>();
|
|
AU.addPreserved<DominatorTreeWrapperPass>();
|
|
|
|
AU.addRequired<LoopInfo>();
|
|
AU.addPreserved<LoopInfo>();
|
|
|
|
AU.addPreserved<AliasAnalysis>();
|
|
AU.addPreserved<ScalarEvolution>();
|
|
AU.addPreserved<DependenceAnalysis>();
|
|
AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
|
|
}
|
|
|
|
/// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
|
|
void verifyAnalysis() const;
|
|
|
|
private:
|
|
bool ProcessLoop(Loop *L);
|
|
BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
|
|
Loop *SeparateNestedLoop(Loop *L, BasicBlock *Preheader);
|
|
BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
|
|
};
|
|
}
|
|
|
|
char LoopSimplify::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(LoopSimplify, "loop-simplify",
|
|
"Canonicalize natural loops", true, false)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
|
|
INITIALIZE_PASS_END(LoopSimplify, "loop-simplify",
|
|
"Canonicalize natural loops", true, false)
|
|
|
|
// Publicly exposed interface to pass...
|
|
char &llvm::LoopSimplifyID = LoopSimplify::ID;
|
|
Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
|
|
|
|
/// runOnLoop - Run down all loops in the CFG (recursively, but we could do
|
|
/// it in any convenient order) inserting preheaders...
|
|
///
|
|
bool LoopSimplify::runOnFunction(Function &F) {
|
|
bool Changed = false;
|
|
AA = getAnalysisIfAvailable<AliasAnalysis>();
|
|
LI = &getAnalysis<LoopInfo>();
|
|
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
SE = getAnalysisIfAvailable<ScalarEvolution>();
|
|
|
|
// Simplify each loop nest in the function.
|
|
for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
|
|
Changed |= simplifyLoop(*I, DT, LI, this, AA, SE);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
// FIXME: Restore this code when we re-enable verification in verifyAnalysis
|
|
// below.
|
|
#if 0
|
|
static void verifyLoop(Loop *L) {
|
|
// Verify subloops.
|
|
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
|
|
verifyLoop(*I);
|
|
|
|
// It used to be possible to just assert L->isLoopSimplifyForm(), however
|
|
// with the introduction of indirectbr, there are now cases where it's
|
|
// not possible to transform a loop as necessary. We can at least check
|
|
// that there is an indirectbr near any time there's trouble.
|
|
|
|
// Indirectbr can interfere with preheader and unique backedge insertion.
|
|
if (!L->getLoopPreheader() || !L->getLoopLatch()) {
|
|
bool HasIndBrPred = false;
|
|
for (pred_iterator PI = pred_begin(L->getHeader()),
|
|
PE = pred_end(L->getHeader()); PI != PE; ++PI)
|
|
if (isa<IndirectBrInst>((*PI)->getTerminator())) {
|
|
HasIndBrPred = true;
|
|
break;
|
|
}
|
|
assert(HasIndBrPred &&
|
|
"LoopSimplify has no excuse for missing loop header info!");
|
|
(void)HasIndBrPred;
|
|
}
|
|
|
|
// Indirectbr can interfere with exit block canonicalization.
|
|
if (!L->hasDedicatedExits()) {
|
|
bool HasIndBrExiting = false;
|
|
SmallVector<BasicBlock*, 8> ExitingBlocks;
|
|
L->getExitingBlocks(ExitingBlocks);
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
|
|
if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
|
|
HasIndBrExiting = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
assert(HasIndBrExiting &&
|
|
"LoopSimplify has no excuse for missing exit block info!");
|
|
(void)HasIndBrExiting;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
void LoopSimplify::verifyAnalysis() const {
|
|
// FIXME: This routine is being called mid-way through the loop pass manager
|
|
// as loop passes destroy this analysis. That's actually fine, but we have no
|
|
// way of expressing that here. Once all of the passes that destroy this are
|
|
// hoisted out of the loop pass manager we can add back verification here.
|
|
#if 0
|
|
for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
|
|
verifyLoop(*I);
|
|
#endif
|
|
}
|