[llvm-commits] [llvm] r83748 - /llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
Chris Lattner
sabre at nondot.org
Sat Oct 10 19:53:37 PDT 2009
Author: lattner
Date: Sat Oct 10 21:53:37 2009
New Revision: 83748
URL: http://llvm.org/viewvc/llvm-project?rev=83748&view=rev
Log:
rewrite LCSSA to use SSAUpdate, to only return true if it modifies
the IR, and to implement the FIXME'd optimization.
Modified:
llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
Modified: llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LCSSA.cpp?rev=83748&r1=83747&r2=83748&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LCSSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LCSSA.cpp Sat Oct 10 21:53:37 2009
@@ -33,22 +33,19 @@
#include "llvm/Pass.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/PredIteratorCache.h"
-#include <map>
using namespace llvm;
STATISTIC(NumLCSSA, "Number of live out of a loop variables");
namespace {
- struct VISIBILITY_HIDDEN LCSSA : public LoopPass {
+ struct LCSSA : public LoopPass {
static char ID; // Pass identification, replacement for typeid
LCSSA() : LoopPass(&ID) {}
@@ -83,8 +80,8 @@
AU.addPreserved<DominanceFrontier>();
}
private:
- void ProcessInstruction(Instruction* Instr,
- const SmallVector<BasicBlock*, 8>& exitBlocks);
+ bool ProcessInstruction(Instruction *Inst,
+ const SmallVectorImpl<BasicBlock*> &ExitBlocks);
/// verifyAnalysis() - Verify loop nest.
virtual void verifyAnalysis() const {
@@ -92,12 +89,6 @@
assert(L->isLCSSAForm() && "LCSSA form not preserved!");
}
- void getLoopValuesUsedOutsideLoop(Loop *L,
- SmallVectorImpl<Instruction*> &AffectedValues);
-
- Value *GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
- DenseMap<DomTreeNode*, Value*> &Phis);
-
/// inLoop - returns true if the given block is within the current loop
bool inLoop(BasicBlock *B) const {
return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
@@ -111,178 +102,163 @@
Pass *llvm::createLCSSAPass() { return new LCSSA(); }
const PassInfo *const llvm::LCSSAID = &X;
+
+/// BlockDominatesAnExit - Return true if the specified block dominates at least
+/// one of the blocks in the specified list.
+static bool BlockDominatesAnExit(BasicBlock *BB,
+ const SmallVectorImpl<BasicBlock*> &ExitBlocks,
+ DominatorTree *DT) {
+ DomTreeNode *DomNode = DT->getNode(BB);
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (DT->dominates(DomNode, DT->getNode(ExitBlocks[i])))
+ return true;
+
+ return false;
+}
+
+
/// runOnFunction - Process all loops in the function, inner-most out.
-bool LCSSA::runOnLoop(Loop *l, LPPassManager &LPM) {
- L = l;
- PredCache.clear();
+bool LCSSA::runOnLoop(Loop *TheLoop, LPPassManager &LPM) {
+ L = TheLoop;
LI = &LPM.getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
+ // Get the set of exiting blocks.
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ L->getExitBlocks(ExitBlocks);
+
+ if (ExitBlocks.empty())
+ return false;
+
// Speed up queries by creating a sorted vector of blocks.
LoopBlocks.clear();
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
array_pod_sort(LoopBlocks.begin(), LoopBlocks.end());
- SmallVector<Instruction*, 16> AffectedValues;
- getLoopValuesUsedOutsideLoop(L, AffectedValues);
-
- // If no values are affected, we can save a lot of work, since we know that
- // nothing will be changed.
- if (AffectedValues.empty())
- return false;
-
- SmallVector<BasicBlock*, 8> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
+ // Look at all the instructions in the loop, checking to see if they have uses
+ // outside the loop. If so, rewrite those uses.
+ bool MadeChange = false;
- // Iterate over all affected values for this loop and insert Phi nodes
- // for them in the appropriate exit blocks.
- for (SmallVectorImpl<Instruction*>::iterator I = AffectedValues.begin(),
- E = AffectedValues.end(); I != E; ++I)
- ProcessInstruction(*I, ExitBlocks);
+ for (Loop::block_iterator BBI = L->block_begin(), E = L->block_end();
+ BBI != E; ++BBI) {
+ BasicBlock *BB = *BBI;
+
+ // For large loops, avoid use-scanning by using dominance information: In
+ // particular, if a block does not dominate any of the loop exits, then none
+ // of the values defined in the block could be used outside the loop.
+ if (!BlockDominatesAnExit(BB, ExitBlocks, DT))
+ continue;
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end();
+ I != E; ++I) {
+ // Reject two common cases fast: instructions with no uses (like stores)
+ // and instructions with one use that is in the same block as this.
+ if (I->use_empty() ||
+ (I->hasOneUse() && I->use_back()->getParent() == BB &&
+ !isa<PHINode>(I->use_back())))
+ continue;
+
+ MadeChange |= ProcessInstruction(I, ExitBlocks);
+ }
+ }
assert(L->isLCSSAForm());
-
- return true;
-}
+ PredCache.clear();
-/// processInstruction - Given a live-out instruction, insert LCSSA Phi nodes,
-/// eliminate all out-of-loop uses.
-void LCSSA::ProcessInstruction(Instruction *Instr,
- const SmallVector<BasicBlock*, 8> &ExitBlocks) {
- ++NumLCSSA; // We are applying the transformation
+ return MadeChange;
+}
- // Keep track of the blocks that have the value available already.
- DenseMap<DomTreeNode*, Value*> Phis;
+/// isExitBlock - Return true if the specified block is in the list.
+static bool isExitBlock(BasicBlock *BB,
+ const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (ExitBlocks[i] == BB)
+ return true;
+ return false;
+}
- BasicBlock *DomBB = Instr->getParent();
+/// ProcessInstruction - Given an instruction in the loop, check to see if it
+/// has any uses that are outside the current loop. If so, insert LCSSA PHI
+/// nodes and rewrite the uses.
+bool LCSSA::ProcessInstruction(Instruction *Inst,
+ const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
+ SmallVector<Use*, 16> UsesToRewrite;
+
+ BasicBlock *InstBB = Inst->getParent();
+
+ for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
+ UI != E; ++UI) {
+ BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(*UI))
+ UserBB = PN->getIncomingBlock(UI);
+
+ if (InstBB != UserBB && !inLoop(UserBB))
+ UsesToRewrite.push_back(&UI.getUse());
+ }
+
+ // If there are no uses outside the loop, exit with no change.
+ if (UsesToRewrite.empty()) return false;
+
+ ++NumLCSSA; // We are applying the transformation
// Invoke instructions are special in that their result value is not available
// along their unwind edge. The code below tests to see whether DomBB dominates
// the value, so adjust DomBB to the normal destination block, which is
// effectively where the value is first usable.
- if (InvokeInst *Inv = dyn_cast<InvokeInst>(Instr))
+ BasicBlock *DomBB = Inst->getParent();
+ if (InvokeInst *Inv = dyn_cast<InvokeInst>(Inst))
DomBB = Inv->getNormalDest();
DomTreeNode *DomNode = DT->getNode(DomBB);
- // Insert the LCSSA phi's into the exit blocks (dominated by the value), and
- // add them to the Phi's map.
- for (SmallVector<BasicBlock*, 8>::const_iterator BBI = ExitBlocks.begin(),
+ SSAUpdater SSAUpdate;
+ SSAUpdate.Initialize(Inst);
+
+ // Insert the LCSSA phi's into all of the exit blocks dominated by the
+ // value., and add them to the Phi's map.
+ for (SmallVectorImpl<BasicBlock*>::const_iterator BBI = ExitBlocks.begin(),
BBE = ExitBlocks.end(); BBI != BBE; ++BBI) {
- BasicBlock *BB = *BBI;
- DomTreeNode *ExitBBNode = DT->getNode(BB);
- Value *&Phi = Phis[ExitBBNode];
- if (!Phi && DT->dominates(DomNode, ExitBBNode)) {
- PHINode *PN = PHINode::Create(Instr->getType(), Instr->getName()+".lcssa",
- BB->begin());
- PN->reserveOperandSpace(PredCache.GetNumPreds(BB));
-
- // Remember that this phi makes the value alive in this block.
- Phi = PN;
-
- // Add inputs from inside the loop for this PHI.
- for (BasicBlock** PI = PredCache.GetPreds(BB); *PI; ++PI)
- PN->addIncoming(Instr, *PI);
- }
+ BasicBlock *ExitBB = *BBI;
+ if (!DT->dominates(DomNode, DT->getNode(ExitBB))) continue;
+
+ // If we already inserted something for this BB, don't reprocess it.
+ if (SSAUpdate.HasValueForBlock(ExitBB)) continue;
+
+ PHINode *PN = PHINode::Create(Inst->getType(), Inst->getName()+".lcssa",
+ ExitBB->begin());
+ PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB));
+
+ // Add inputs from inside the loop for this PHI.
+ for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI)
+ PN->addIncoming(Inst, *PI);
+
+ // Remember that this phi makes the value alive in this block.
+ SSAUpdate.AddAvailableValue(ExitBB, PN);
}
-
- // Record all uses of Instr outside the loop. We need to rewrite these. The
- // LCSSA phis won't be included because they use the value in the loop.
- for (Value::use_iterator UI = Instr->use_begin(), E = Instr->use_end();
- UI != E;) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (PHINode *P = dyn_cast<PHINode>(*UI))
- UserBB = P->getIncomingBlock(UI);
-
- // If the user is in the loop, don't rewrite it!
- if (UserBB == Instr->getParent() || inLoop(UserBB)) {
- ++UI;
+ // Rewrite all uses outside the loop in terms of the new PHIs we just
+ // inserted.
+ for (unsigned i = 0, e = UsesToRewrite.size(); i != e; ++i) {
+ // If this use is in an exit block, rewrite to use the newly inserted PHI.
+ // This is required for correctness because SSAUpdate doesn't handle uses in
+ // the same block. It assumes the PHI we inserted is at the end of the
+ // block.
+ Instruction *User = cast<Instruction>(UsesToRewrite[i]->getUser());
+ BasicBlock *UserBB = User->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(User))
+ UserBB = PN->getIncomingBlock(*UsesToRewrite[i]);
+
+ if (isa<PHINode>(UserBB->begin()) &&
+ isExitBlock(UserBB, ExitBlocks)) {
+ UsesToRewrite[i]->set(UserBB->begin());
continue;
}
- // Otherwise, patch up uses of the value with the appropriate LCSSA Phi,
- // inserting PHI nodes into join points where needed.
- Value *Val = GetValueForBlock(DT->getNode(UserBB), Instr, Phis);
-
- // Preincrement the iterator to avoid invalidating it when we change the
- // value.
- Use &U = UI.getUse();
- ++UI;
- U.set(Val);
+ // Otherwise, do full PHI insertion.
+ SSAUpdate.RewriteUse(*UsesToRewrite[i]);
}
-}
-
-/// getLoopValuesUsedOutsideLoop - Return any values defined in the loop that
-/// are used by instructions outside of it.
-void LCSSA::getLoopValuesUsedOutsideLoop(Loop *L,
- SmallVectorImpl<Instruction*> &AffectedValues) {
- // FIXME: For large loops, we may be able to avoid a lot of use-scanning
- // by using dominance information. In particular, if a block does not
- // dominate any of the loop exits, then none of the values defined in the
- // block could be used outside the loop.
- for (Loop::block_iterator BB = L->block_begin(), BE = L->block_end();
- BB != BE; ++BB) {
- for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
- for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (PHINode *PN = dyn_cast<PHINode>(*UI))
- UserBB = PN->getIncomingBlock(UI);
-
- if (*BB != UserBB && !inLoop(UserBB)) {
- AffectedValues.push_back(I);
- break;
- }
- }
- }
-}
-
-/// GetValueForBlock - Get the value to use within the specified basic block.
-/// available values are in Phis.
-Value *LCSSA::GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
- DenseMap<DomTreeNode*, Value*> &Phis) {
- // If there is no dominator info for this BB, it is unreachable.
- if (BB == 0)
- return UndefValue::get(OrigInst->getType());
-
- // If we have already computed this value, return the previously computed val.
- if (Phis.count(BB)) return Phis[BB];
-
- DomTreeNode *IDom = BB->getIDom();
-
- // Otherwise, there are two cases: we either have to insert a PHI node or we
- // don't. We need to insert a PHI node if this block is not dominated by one
- // of the exit nodes from the loop (the loop could have multiple exits, and
- // though the value defined *inside* the loop dominated all its uses, each
- // exit by itself may not dominate all the uses).
- //
- // The simplest way to check for this condition is by checking to see if the
- // idom is in the loop. If so, we *know* that none of the exit blocks
- // dominate this block. Note that we *know* that the block defining the
- // original instruction is in the idom chain, because if it weren't, then the
- // original value didn't dominate this use.
- if (!inLoop(IDom->getBlock())) {
- // Idom is not in the loop, we must still be "below" the exit block and must
- // be fully dominated by the value live in the idom.
- Value* val = GetValueForBlock(IDom, OrigInst, Phis);
- Phis.insert(std::make_pair(BB, val));
- return val;
- }
-
- BasicBlock *BBN = BB->getBlock();
- // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
- // now, then get values to fill in the incoming values for the PHI.
- PHINode *PN = PHINode::Create(OrigInst->getType(),
- OrigInst->getName() + ".lcssa", BBN->begin());
- PN->reserveOperandSpace(PredCache.GetNumPreds(BBN));
- Phis.insert(std::make_pair(BB, PN));
-
- // Fill in the incoming values for the block.
- for (BasicBlock **PI = PredCache.GetPreds(BBN); *PI; ++PI)
- PN->addIncoming(GetValueForBlock(DT->getNode(*PI), OrigInst, Phis), *PI);
- return PN;
+ return true;
}
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