return find(ExitBlocks, BB) != ExitBlocks.end();
}
-/// 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.
-static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
- const SmallVectorImpl<BasicBlock *> &ExitBlocks,
- PredIteratorCache &PredCache, LoopInfo *LI) {
+/// For every instruction from the worklist, 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 llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
+ DominatorTree &DT, LoopInfo &LI) {
SmallVector<Use *, 16> UsesToRewrite;
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ PredIteratorCache PredCache;
+ bool Changed = false;
- // Tokens cannot be used in PHI nodes, so we skip over them.
- // We can run into tokens which are live out of a loop with catchswitch
- // instructions in Windows EH if the catchswitch has one catchpad which
- // is inside the loop and another which is not.
- if (Inst.getType()->isTokenTy())
- return false;
+ while (!Worklist.empty()) {
+ UsesToRewrite.clear();
+ ExitBlocks.clear();
- BasicBlock *InstBB = Inst.getParent();
+ Instruction *I = Worklist.pop_back_val();
+ BasicBlock *InstBB = I->getParent();
+ Loop *L = LI.getLoopFor(InstBB);
+ L->getExitBlocks(ExitBlocks);
- for (Use &U : Inst.uses()) {
- Instruction *User = cast<Instruction>(U.getUser());
- BasicBlock *UserBB = User->getParent();
- if (PHINode *PN = dyn_cast<PHINode>(User))
- UserBB = PN->getIncomingBlock(U);
+ if (ExitBlocks.empty())
+ continue;
- if (InstBB != UserBB && !L.contains(UserBB))
- UsesToRewrite.push_back(&U);
- }
+ // Tokens cannot be used in PHI nodes, so we skip over them.
+ // We can run into tokens which are live out of a loop with catchswitch
+ // instructions in Windows EH if the catchswitch has one catchpad which
+ // is inside the loop and another which is not.
+ if (I->getType()->isTokenTy())
+ continue;
- // If there are no uses outside the loop, exit with no change.
- if (UsesToRewrite.empty())
- return false;
+ for (Use &U : I->uses()) {
+ Instruction *User = cast<Instruction>(U.getUser());
+ BasicBlock *UserBB = User->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(User))
+ UserBB = PN->getIncomingBlock(U);
- ++NumLCSSA; // We are applying the transformation
+ if (InstBB != UserBB && !L->contains(UserBB))
+ UsesToRewrite.push_back(&U);
+ }
- // 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.
- BasicBlock *DomBB = Inst.getParent();
- if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
- DomBB = Inv->getNormalDest();
+ // If there are no uses outside the loop, exit with no change.
+ if (UsesToRewrite.empty())
+ continue;
- DomTreeNode *DomNode = DT.getNode(DomBB);
+ ++NumLCSSA; // We are applying the transformation
- SmallVector<PHINode *, 16> AddedPHIs;
- SmallVector<PHINode *, 8> PostProcessPHIs;
+ // 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.
+ BasicBlock *DomBB = InstBB;
+ if (InvokeInst *Inv = dyn_cast<InvokeInst>(I))
+ DomBB = Inv->getNormalDest();
- SSAUpdater SSAUpdate;
- SSAUpdate.Initialize(Inst.getType(), Inst.getName());
+ DomTreeNode *DomNode = DT.getNode(DomBB);
- // Insert the LCSSA phi's into all of the exit blocks dominated by the
- // value, and add them to the Phi's map.
- for (BasicBlock *ExitBB : ExitBlocks) {
- if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
- continue;
+ SmallVector<PHINode *, 16> AddedPHIs;
+ SmallVector<PHINode *, 8> PostProcessPHIs;
- // If we already inserted something for this BB, don't reprocess it.
- if (SSAUpdate.HasValueForBlock(ExitBB))
- continue;
+ SSAUpdater SSAUpdate;
+ SSAUpdate.Initialize(I->getType(), I->getName());
- PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB),
- Inst.getName() + ".lcssa", &ExitBB->front());
+ // Insert the LCSSA phi's into all of the exit blocks dominated by the
+ // value, and add them to the Phi's map.
+ for (BasicBlock *ExitBB : ExitBlocks) {
+ if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
+ continue;
- // Add inputs from inside the loop for this PHI.
- for (BasicBlock *Pred : PredCache.get(ExitBB)) {
- PN->addIncoming(&Inst, Pred);
+ // If we already inserted something for this BB, don't reprocess it.
+ if (SSAUpdate.HasValueForBlock(ExitBB))
+ continue;
- // If the exit block has a predecessor not within the loop, arrange for
- // the incoming value use corresponding to that predecessor to be
- // rewritten in terms of a different LCSSA PHI.
- if (!L.contains(Pred))
- UsesToRewrite.push_back(
- &PN->getOperandUse(PN->getOperandNumForIncomingValue(
- PN->getNumIncomingValues() - 1)));
+ PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
+ I->getName() + ".lcssa", &ExitBB->front());
+
+ // Add inputs from inside the loop for this PHI.
+ for (BasicBlock *Pred : PredCache.get(ExitBB)) {
+ PN->addIncoming(I, Pred);
+
+ // If the exit block has a predecessor not within the loop, arrange for
+ // the incoming value use corresponding to that predecessor to be
+ // rewritten in terms of a different LCSSA PHI.
+ if (!L->contains(Pred))
+ UsesToRewrite.push_back(
+ &PN->getOperandUse(PN->getOperandNumForIncomingValue(
+ PN->getNumIncomingValues() - 1)));
+ }
+
+ AddedPHIs.push_back(PN);
+
+ // Remember that this phi makes the value alive in this block.
+ SSAUpdate.AddAvailableValue(ExitBB, PN);
+
+ // LoopSimplify might fail to simplify some loops (e.g. when indirect
+ // branches are involved). In such situations, it might happen that an
+ // exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we
+ // create PHIs in such an exit block, we are also inserting PHIs into L2's
+ // header. This could break LCSSA form for L2 because these inserted PHIs
+ // can also have uses outside of L2. Remember all PHIs in such situation
+ // as to revisit than later on. FIXME: Remove this if indirectbr support
+ // into LoopSimplify gets improved.
+ if (auto *OtherLoop = LI.getLoopFor(ExitBB))
+ if (!L->contains(OtherLoop))
+ PostProcessPHIs.push_back(PN);
}
- AddedPHIs.push_back(PN);
-
- // Remember that this phi makes the value alive in this block.
- SSAUpdate.AddAvailableValue(ExitBB, PN);
-
- // LoopSimplify might fail to simplify some loops (e.g. when indirect
- // branches are involved). In such situations, it might happen that an exit
- // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
- // PHIs in such an exit block, we are also inserting PHIs into L2's header.
- // This could break LCSSA form for L2 because these inserted PHIs can also
- // have uses outside of L2. Remember all PHIs in such situation as to
- // revisit than later on. FIXME: Remove this if indirectbr support into
- // LoopSimplify gets improved.
- if (auto *OtherLoop = LI->getLoopFor(ExitBB))
- if (!L.contains(OtherLoop))
- PostProcessPHIs.push_back(PN);
- }
+ // Rewrite all uses outside the loop in terms of the new PHIs we just
+ // inserted.
+ for (Use *UseToRewrite : UsesToRewrite) {
+ // 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>(UseToRewrite->getUser());
+ BasicBlock *UserBB = User->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(User))
+ UserBB = PN->getIncomingBlock(*UseToRewrite);
+
+ if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
+ // Tell the VHs that the uses changed. This updates SCEV's caches.
+ if (UseToRewrite->get()->hasValueHandle())
+ ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
+ UseToRewrite->set(&UserBB->front());
+ continue;
+ }
- // Rewrite all uses outside the loop in terms of the new PHIs we just
- // inserted.
- for (Use *UseToRewrite : UsesToRewrite) {
- // 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>(UseToRewrite->getUser());
- BasicBlock *UserBB = User->getParent();
- if (PHINode *PN = dyn_cast<PHINode>(User))
- UserBB = PN->getIncomingBlock(*UseToRewrite);
-
- if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
- // Tell the VHs that the uses changed. This updates SCEV's caches.
- if (UseToRewrite->get()->hasValueHandle())
- ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front());
- UseToRewrite->set(&UserBB->front());
- continue;
+ // Otherwise, do full PHI insertion.
+ SSAUpdate.RewriteUse(*UseToRewrite);
}
- // Otherwise, do full PHI insertion.
- SSAUpdate.RewriteUse(*UseToRewrite);
- }
+ // Post process PHI instructions that were inserted into another disjoint
+ // loop and update their exits properly.
+ for (auto *PostProcessPN : PostProcessPHIs) {
+ if (PostProcessPN->use_empty())
+ continue;
- // Post process PHI instructions that were inserted into another disjoint loop
- // and update their exits properly.
- for (auto *I : PostProcessPHIs) {
- if (I->use_empty())
- continue;
+ // Reprocess each PHI instruction.
+ Worklist.push_back(PostProcessPN);
+ }
- BasicBlock *PHIBB = I->getParent();
- Loop *OtherLoop = LI->getLoopFor(PHIBB);
- SmallVector<BasicBlock *, 8> EBs;
- OtherLoop->getExitBlocks(EBs);
- if (EBs.empty())
- continue;
+ // Remove PHI nodes that did not have any uses rewritten.
+ for (PHINode *PN : AddedPHIs)
+ if (PN->use_empty())
+ PN->eraseFromParent();
- // Recurse and re-process each PHI instruction. FIXME: we should really
- // convert this entire thing to a worklist approach where we process a
- // vector of instructions...
- processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
+ Changed = true;
}
-
- // Remove PHI nodes that did not have any uses rewritten.
- for (PHINode *PN : AddedPHIs)
- if (PN->use_empty())
- PN->eraseFromParent();
-
- return true;
+ return Changed;
}
/// Return true if the specified block dominates at least
if (ExitBlocks.empty())
return false;
- PredIteratorCache PredCache;
+ SmallVector<Instruction *, 8> Worklist;
// Look at all the instructions in the loop, checking to see if they have uses
- // outside the loop. If so, rewrite those uses.
+ // outside the loop. If so, put them into the worklist to rewrite those uses.
for (BasicBlock *BB : L.blocks()) {
// 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
!isa<PHINode>(I.user_back())))
continue;
- Changed |= processInstruction(L, I, DT, ExitBlocks, PredCache, LI);
+ Worklist.push_back(&I);
}
}
+ Changed = formLCSSAForInstructions(Worklist, DT, *LI);
// If we modified the code, remove any caches about the loop from SCEV to
// avoid dangling entries.