forked from OSchip/llvm-project
Make processInstruction from LCSSA.cpp externally available.
Summary: When a pass tries to keep LCSSA form it's often convenient to be able to update LCSSA for a set of instructions rather than for the entire loop. This patch makes the processInstruction from LCSSA externally available under a name formLCSSAForInstruction. Reviewers: chandlerc, sanjoy, hfinkel Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D22378 llvm-svn: 275613
This commit is contained in:
Michael Zolotukhin
parent
3cbf3f1f59
commit
a78937afb2
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@ -323,6 +323,20 @@ private:
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BasicBlock *InsertPreheaderForLoop(Loop *L, DominatorTree *DT, LoopInfo *LI,
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bool PreserveLCSSA);
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/// Ensures LCSSA form for every instruction from the Worklist in the scope of
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/// innermost containing loop.
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///
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/// For the given instruction which have uses outside of the loop, an LCSSA PHI
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/// node is inserted and the uses outside the loop are rewritten to use this
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/// node.
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///
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/// LoopInfo and DominatorTree are required and, since the routine makes no
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/// changes to CFG, preserved.
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///
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/// Returns true if any modifications are made.
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bool formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
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DominatorTree &DT, LoopInfo &LI);
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/// \brief Put loop into LCSSA form.
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///
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/// Looks at all instructions in the loop which have uses outside of the
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@ -57,148 +57,153 @@ static bool isExitBlock(BasicBlock *BB,
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return find(ExitBlocks, BB) != ExitBlocks.end();
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}
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/// Given an instruction in the loop, check to see if it has any uses that are
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/// outside the current loop. If so, insert LCSSA PHI nodes and rewrite the
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/// uses.
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static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
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const SmallVectorImpl<BasicBlock *> &ExitBlocks,
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PredIteratorCache &PredCache, LoopInfo *LI) {
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/// For every instruction from the worklist, check to see if it has any uses
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/// that are outside the current loop. If so, insert LCSSA PHI nodes and
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/// rewrite the uses.
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bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
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DominatorTree &DT, LoopInfo &LI) {
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SmallVector<Use *, 16> UsesToRewrite;
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SmallVector<BasicBlock *, 8> ExitBlocks;
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PredIteratorCache PredCache;
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bool Changed = false;
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// Tokens cannot be used in PHI nodes, so we skip over them.
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// We can run into tokens which are live out of a loop with catchswitch
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// instructions in Windows EH if the catchswitch has one catchpad which
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// is inside the loop and another which is not.
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if (Inst.getType()->isTokenTy())
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return false;
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while (!Worklist.empty()) {
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UsesToRewrite.clear();
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ExitBlocks.clear();
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BasicBlock *InstBB = Inst.getParent();
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Instruction *I = Worklist.pop_back_val();
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BasicBlock *InstBB = I->getParent();
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Loop *L = LI.getLoopFor(InstBB);
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L->getExitBlocks(ExitBlocks);
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for (Use &U : Inst.uses()) {
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Instruction *User = cast<Instruction>(U.getUser());
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BasicBlock *UserBB = User->getParent();
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if (PHINode *PN = dyn_cast<PHINode>(User))
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UserBB = PN->getIncomingBlock(U);
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if (InstBB != UserBB && !L.contains(UserBB))
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UsesToRewrite.push_back(&U);
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}
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// If there are no uses outside the loop, exit with no change.
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if (UsesToRewrite.empty())
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return false;
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++NumLCSSA; // We are applying the transformation
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// Invoke instructions are special in that their result value is not available
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// along their unwind edge. The code below tests to see whether DomBB
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// dominates the value, so adjust DomBB to the normal destination block,
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// which is effectively where the value is first usable.
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BasicBlock *DomBB = Inst.getParent();
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if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
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DomBB = Inv->getNormalDest();
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DomTreeNode *DomNode = DT.getNode(DomBB);
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SmallVector<PHINode *, 16> AddedPHIs;
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SmallVector<PHINode *, 8> PostProcessPHIs;
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SSAUpdater SSAUpdate;
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SSAUpdate.Initialize(Inst.getType(), Inst.getName());
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// Insert the LCSSA phi's into all of the exit blocks dominated by the
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// value, and add them to the Phi's map.
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for (BasicBlock *ExitBB : ExitBlocks) {
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if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
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if (ExitBlocks.empty())
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continue;
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// If we already inserted something for this BB, don't reprocess it.
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if (SSAUpdate.HasValueForBlock(ExitBB))
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// Tokens cannot be used in PHI nodes, so we skip over them.
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// We can run into tokens which are live out of a loop with catchswitch
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// instructions in Windows EH if the catchswitch has one catchpad which
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// is inside the loop and another which is not.
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if (I->getType()->isTokenTy())
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continue;
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PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
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Inst.getName() + ".lcssa", &ExitBB->front());
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for (Use &U : I->uses()) {
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Instruction *User = cast<Instruction>(U.getUser());
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BasicBlock *UserBB = User->getParent();
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if (PHINode *PN = dyn_cast<PHINode>(User))
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UserBB = PN->getIncomingBlock(U);
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// Add inputs from inside the loop for this PHI.
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for (BasicBlock *Pred : PredCache.get(ExitBB)) {
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PN->addIncoming(&Inst, Pred);
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// If the exit block has a predecessor not within the loop, arrange for
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// the incoming value use corresponding to that predecessor to be
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// rewritten in terms of a different LCSSA PHI.
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if (!L.contains(Pred))
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UsesToRewrite.push_back(
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&PN->getOperandUse(PN->getOperandNumForIncomingValue(
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PN->getNumIncomingValues() - 1)));
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if (InstBB != UserBB && !L->contains(UserBB))
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UsesToRewrite.push_back(&U);
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}
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AddedPHIs.push_back(PN);
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// Remember that this phi makes the value alive in this block.
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SSAUpdate.AddAvailableValue(ExitBB, PN);
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// LoopSimplify might fail to simplify some loops (e.g. when indirect
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// branches are involved). In such situations, it might happen that an exit
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// for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
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// PHIs in such an exit block, we are also inserting PHIs into L2's header.
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// This could break LCSSA form for L2 because these inserted PHIs can also
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// have uses outside of L2. Remember all PHIs in such situation as to
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// revisit than later on. FIXME: Remove this if indirectbr support into
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// LoopSimplify gets improved.
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if (auto *OtherLoop = LI->getLoopFor(ExitBB))
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if (!L.contains(OtherLoop))
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PostProcessPHIs.push_back(PN);
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}
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// Rewrite all uses outside the loop in terms of the new PHIs we just
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// inserted.
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for (Use *UseToRewrite : UsesToRewrite) {
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// If this use is in an exit block, rewrite to use the newly inserted PHI.
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// This is required for correctness because SSAUpdate doesn't handle uses in
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// the same block. It assumes the PHI we inserted is at the end of the
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// block.
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Instruction *User = cast<Instruction>(UseToRewrite->getUser());
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BasicBlock *UserBB = User->getParent();
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if (PHINode *PN = dyn_cast<PHINode>(User))
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UserBB = PN->getIncomingBlock(*UseToRewrite);
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if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
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// Tell the VHs that the uses changed. This updates SCEV's caches.
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if (UseToRewrite->get()->hasValueHandle())
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ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
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UseToRewrite->set(&UserBB->front());
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// If there are no uses outside the loop, exit with no change.
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if (UsesToRewrite.empty())
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continue;
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++NumLCSSA; // We are applying the transformation
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// Invoke instructions are special in that their result value is not
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// available along their unwind edge. The code below tests to see whether
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// DomBB dominates the value, so adjust DomBB to the normal destination
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// block, which is effectively where the value is first usable.
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BasicBlock *DomBB = InstBB;
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if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
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DomBB = Inv->getNormalDest();
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DomTreeNode *DomNode = DT.getNode(DomBB);
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SmallVector<PHINode *, 16> AddedPHIs;
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SmallVector<PHINode *, 8> PostProcessPHIs;
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SSAUpdater SSAUpdate;
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SSAUpdate.Initialize(I->getType(), I->getName());
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// Insert the LCSSA phi's into all of the exit blocks dominated by the
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// value, and add them to the Phi's map.
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for (BasicBlock *ExitBB : ExitBlocks) {
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if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
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continue;
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// If we already inserted something for this BB, don't reprocess it.
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if (SSAUpdate.HasValueForBlock(ExitBB))
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continue;
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PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
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I->getName() + ".lcssa", &ExitBB->front());
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// Add inputs from inside the loop for this PHI.
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for (BasicBlock *Pred : PredCache.get(ExitBB)) {
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PN->addIncoming(I, Pred);
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// If the exit block has a predecessor not within the loop, arrange for
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// the incoming value use corresponding to that predecessor to be
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// rewritten in terms of a different LCSSA PHI.
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if (!L->contains(Pred))
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UsesToRewrite.push_back(
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&PN->getOperandUse(PN->getOperandNumForIncomingValue(
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PN->getNumIncomingValues() - 1)));
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}
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AddedPHIs.push_back(PN);
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// Remember that this phi makes the value alive in this block.
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SSAUpdate.AddAvailableValue(ExitBB, PN);
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// LoopSimplify might fail to simplify some loops (e.g. when indirect
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// branches are involved). In such situations, it might happen that an
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// exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we
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// create PHIs in such an exit block, we are also inserting PHIs into L2's
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// header. This could break LCSSA form for L2 because these inserted PHIs
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// can also have uses outside of L2. Remember all PHIs in such situation
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// as to revisit than later on. FIXME: Remove this if indirectbr support
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// into LoopSimplify gets improved.
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if (auto *OtherLoop = LI.getLoopFor(ExitBB))
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if (!L->contains(OtherLoop))
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PostProcessPHIs.push_back(PN);
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}
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// Otherwise, do full PHI insertion.
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SSAUpdate.RewriteUse(*UseToRewrite);
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// Rewrite all uses outside the loop in terms of the new PHIs we just
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// inserted.
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for (Use *UseToRewrite : UsesToRewrite) {
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// If this use is in an exit block, rewrite to use the newly inserted PHI.
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// This is required for correctness because SSAUpdate doesn't handle uses
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// in the same block. It assumes the PHI we inserted is at the end of the
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// block.
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Instruction *User = cast<Instruction>(UseToRewrite->getUser());
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BasicBlock *UserBB = User->getParent();
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if (PHINode *PN = dyn_cast<PHINode>(User))
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UserBB = PN->getIncomingBlock(*UseToRewrite);
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if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
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// Tell the VHs that the uses changed. This updates SCEV's caches.
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if (UseToRewrite->get()->hasValueHandle())
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ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
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UseToRewrite->set(&UserBB->front());
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continue;
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}
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// Otherwise, do full PHI insertion.
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SSAUpdate.RewriteUse(*UseToRewrite);
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}
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// Post process PHI instructions that were inserted into another disjoint
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// loop and update their exits properly.
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for (auto *PostProcessPN : PostProcessPHIs) {
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if (PostProcessPN->use_empty())
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continue;
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// Reprocess each PHI instruction.
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Worklist.push_back(PostProcessPN);
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}
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// Remove PHI nodes that did not have any uses rewritten.
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for (PHINode *PN : AddedPHIs)
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if (PN->use_empty())
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PN->eraseFromParent();
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Changed = true;
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}
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// Post process PHI instructions that were inserted into another disjoint loop
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// and update their exits properly.
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for (auto *I : PostProcessPHIs) {
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if (I->use_empty())
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continue;
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BasicBlock *PHIBB = I->getParent();
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Loop *OtherLoop = LI->getLoopFor(PHIBB);
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SmallVector<BasicBlock *, 8> EBs;
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OtherLoop->getExitBlocks(EBs);
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if (EBs.empty())
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continue;
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// Recurse and re-process each PHI instruction. FIXME: we should really
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// convert this entire thing to a worklist approach where we process a
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// vector of instructions...
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processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
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}
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// Remove PHI nodes that did not have any uses rewritten.
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for (PHINode *PN : AddedPHIs)
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if (PN->use_empty())
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PN->eraseFromParent();
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return true;
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return Changed;
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}
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/// Return true if the specified block dominates at least
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@ -224,10 +229,10 @@ bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
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if (ExitBlocks.empty())
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return false;
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PredIteratorCache PredCache;
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SmallVector<Instruction *, 8> Worklist;
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// Look at all the instructions in the loop, checking to see if they have uses
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// outside the loop. If so, rewrite those uses.
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// outside the loop. If so, put them into the worklist to rewrite those uses.
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for (BasicBlock *BB : L.blocks()) {
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// For large loops, avoid use-scanning by using dominance information: In
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// particular, if a block does not dominate any of the loop exits, then none
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@ -243,9 +248,10 @@ bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
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!isa<PHINode>(I.user_back())))
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continue;
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Changed |= processInstruction(L, I, DT, ExitBlocks, PredCache, LI);
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Worklist.push_back(&I);
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}
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}
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Changed = formLCSSAForInstructions(Worklist, DT, *LI);
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// If we modified the code, remove any caches about the loop from SCEV to
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// avoid dangling entries.
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