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[Utils] Consolidate LockstepReverseIterator into own header (NFC) (#116657)
Common code has been unified and generalized. Not sure if it may be worth to generalize this further, since it looks closely tied to Blocks (might make sense to rename it in `LockstepReverseInstructionIterator`).
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‎llvm/include/llvm/Transforms/Utils/LockstepReverseIterator.h

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//===- LockstepReverseIterator.h ------------------------------*- C++ -*---===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_UTILS_LOCKSTEPREVERSEITERATOR_H
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#define LLVM_TRANSFORMS_UTILS_LOCKSTEPREVERSEITERATOR_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Instruction.h"
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namespace llvm {
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struct NoActiveBlocksOption {};
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struct ActiveBlocksOption {
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SmallSetVector<BasicBlock *, 4> ActiveBlocks;
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SmallSetVector<BasicBlock *, 4> &getActiveBlocks() { return ActiveBlocks; }
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ActiveBlocksOption() = default;
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};
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/// Iterates through instructions in a set of blocks in reverse order from the
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/// first non-terminator. For example (assume all blocks have size n):
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/// LockstepReverseIterator I([B1, B2, B3]);
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/// *I-- = [B1[n], B2[n], B3[n]];
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/// *I-- = [B1[n-1], B2[n-1], B3[n-1]];
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/// *I-- = [B1[n-2], B2[n-2], B3[n-2]];
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/// ...
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///
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/// The iterator continues processing until all blocks have been exhausted if \p
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/// EarlyFailure is explicitly set to \c false. Use \c getActiveBlocks() to
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/// determine which blocks are still going and the order they appear in the list
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/// returned by operator*.
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template <bool EarlyFailure = true>
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class LockstepReverseIterator
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: private std::conditional_t<EarlyFailure, NoActiveBlocksOption,
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ActiveBlocksOption> {
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private:
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using Base = std::conditional_t<EarlyFailure, NoActiveBlocksOption,
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ActiveBlocksOption>;
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ArrayRef<BasicBlock *> Blocks;
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SmallVector<Instruction *, 4> Insts;
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bool Fail;
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public:
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LockstepReverseIterator(ArrayRef<BasicBlock *> Blocks) : Blocks(Blocks) {
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reset();
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}
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void reset() {
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Fail = false;
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if constexpr (!EarlyFailure) {
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this->ActiveBlocks.clear();
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for (BasicBlock *BB : Blocks)
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this->ActiveBlocks.insert(BB);
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}
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Insts.clear();
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for (BasicBlock *BB : Blocks) {
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Instruction *Prev = BB->getTerminator()->getPrevNonDebugInstruction();
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if (!Prev) {
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// Block wasn't big enough - only contained a terminator.
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if constexpr (EarlyFailure) {
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Fail = true;
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return;
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} else {
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this->ActiveBlocks.remove(BB);
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continue;
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}
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}
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Insts.push_back(Prev);
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}
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if (Insts.empty())
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Fail = true;
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}
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bool isValid() const { return !Fail; }
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ArrayRef<Instruction *> operator*() const { return Insts; }
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// Note: This needs to return a SmallSetVector as the elements of
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// ActiveBlocks will be later copied to Blocks using std::copy. The
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// resultant order of elements in Blocks needs to be deterministic.
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// Using SmallPtrSet instead causes non-deterministic order while
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// copying. And we cannot simply sort Blocks as they need to match the
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// corresponding Values.
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SmallSetVector<BasicBlock *, 4> &getActiveBlocks() {
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return Base::getActiveBlocks();
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}
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void restrictToBlocks(SmallSetVector<BasicBlock *, 4> &Blocks) {
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static_assert(!EarlyFailure, "Unknown method");
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for (auto It = Insts.begin(); It != Insts.end();) {
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if (!Blocks.contains((*It)->getParent())) {
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this->ActiveBlocks.remove((*It)->getParent());
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It = Insts.erase(It);
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} else {
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++It;
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}
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}
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}
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LockstepReverseIterator &operator--() {
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if (Fail)
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return *this;
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SmallVector<Instruction *, 4> NewInsts;
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for (Instruction *Inst : Insts) {
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Instruction *Prev = Inst->getPrevNonDebugInstruction();
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if (!Prev) {
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if constexpr (!EarlyFailure) {
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this->ActiveBlocks.remove(Inst->getParent());
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} else {
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Fail = true;
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return *this;
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}
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} else {
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NewInsts.push_back(Prev);
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}
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}
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if (NewInsts.empty())
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Fail = true;
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else
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Insts = NewInsts;
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return *this;
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}
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LockstepReverseIterator &operator++() {
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static_assert(EarlyFailure, "Unknown method");
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if (Fail)
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return *this;
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SmallVector<Instruction *, 4> NewInsts;
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for (Instruction *Inst : Insts) {
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Instruction *Next = Inst->getNextNonDebugInstruction();
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// Already at end of block.
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if (!Next) {
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Fail = true;
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return *this;
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}
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NewInsts.push_back(Next);
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}
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if (NewInsts.empty())
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Fail = true;
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else
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Insts = NewInsts;
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return *this;
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}
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};
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} // end namespace llvm
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#endif // LLVM_TRANSFORMS_UTILS_LOCKSTEPREVERSEITERATOR_H

‎llvm/lib/Transforms/Scalar/GVNSink.cpp

Lines changed: 8 additions & 86 deletions
Original file line numberDiff line numberDiff line change
@@ -65,6 +65,7 @@
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#include "llvm/Transforms/Scalar/GVNExpression.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LockstepReverseIterator.h"
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
@@ -96,87 +97,6 @@ static bool isMemoryInst(const Instruction *I) {
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(isa<CallInst>(I) && !cast<CallInst>(I)->doesNotAccessMemory());
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}
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/// Iterates through instructions in a set of blocks in reverse order from the
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/// first non-terminator. For example (assume all blocks have size n):
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/// LockstepReverseIterator I([B1, B2, B3]);
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/// *I-- = [B1[n], B2[n], B3[n]];
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/// *I-- = [B1[n-1], B2[n-1], B3[n-1]];
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/// *I-- = [B1[n-2], B2[n-2], B3[n-2]];
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/// ...
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///
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/// It continues until all blocks have been exhausted. Use \c getActiveBlocks()
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/// to
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/// determine which blocks are still going and the order they appear in the
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/// list returned by operator*.
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class LockstepReverseIterator {
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ArrayRef<BasicBlock *> Blocks;
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SmallSetVector<BasicBlock *, 4> ActiveBlocks;
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SmallVector<Instruction *, 4> Insts;
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bool Fail;
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public:
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LockstepReverseIterator(ArrayRef<BasicBlock *> Blocks) : Blocks(Blocks) {
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reset();
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}
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void reset() {
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Fail = false;
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ActiveBlocks.clear();
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for (BasicBlock *BB : Blocks)
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ActiveBlocks.insert(BB);
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Insts.clear();
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for (BasicBlock *BB : Blocks) {
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if (BB->size() <= 1) {
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// Block wasn't big enough - only contained a terminator.
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ActiveBlocks.remove(BB);
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continue;
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}
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Insts.push_back(BB->getTerminator()->getPrevNonDebugInstruction());
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}
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if (Insts.empty())
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Fail = true;
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}
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bool isValid() const { return !Fail; }
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ArrayRef<Instruction *> operator*() const { return Insts; }
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// Note: This needs to return a SmallSetVector as the elements of
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// ActiveBlocks will be later copied to Blocks using std::copy. The
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// resultant order of elements in Blocks needs to be deterministic.
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// Using SmallPtrSet instead causes non-deterministic order while
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// copying. And we cannot simply sort Blocks as they need to match the
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// corresponding Values.
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SmallSetVector<BasicBlock *, 4> &getActiveBlocks() { return ActiveBlocks; }
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void restrictToBlocks(SmallSetVector<BasicBlock *, 4> &Blocks) {
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for (auto II = Insts.begin(); II != Insts.end();) {
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if (!Blocks.contains((*II)->getParent())) {
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ActiveBlocks.remove((*II)->getParent());
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II = Insts.erase(II);
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} else {
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++II;
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}
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}
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}
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void operator--() {
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if (Fail)
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return;
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SmallVector<Instruction *, 4> NewInsts;
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for (auto *Inst : Insts) {
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if (Inst == &Inst->getParent()->front())
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ActiveBlocks.remove(Inst->getParent());
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else
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NewInsts.push_back(Inst->getPrevNonDebugInstruction());
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}
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if (NewInsts.empty()) {
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Fail = true;
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return;
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}
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Insts = NewInsts;
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}
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};
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//===----------------------------------------------------------------------===//
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/// Candidate solution for sinking. There may be different ways to
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/// The main heuristic function. Analyze the set of instructions pointed to by
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/// LRI and return a candidate solution if these instructions can be sunk, or
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/// std::nullopt otherwise.
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std::optional<SinkingInstructionCandidate> analyzeInstructionForSinking(
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LockstepReverseIterator &LRI, unsigned &InstNum, unsigned &MemoryInstNum,
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ModelledPHISet &NeededPHIs, SmallPtrSetImpl<Value *> &PHIContents);
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std::optional<SinkingInstructionCandidate>
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analyzeInstructionForSinking(LockstepReverseIterator<false> &LRI,
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unsigned &InstNum, unsigned &MemoryInstNum,
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ModelledPHISet &NeededPHIs,
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SmallPtrSetImpl<Value *> &PHIContents);
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641563
/// Create a ModelledPHI for each PHI in BB, adding to PHIs.
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void analyzeInitialPHIs(BasicBlock *BB, ModelledPHISet &PHIs,
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};
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677599
std::optional<SinkingInstructionCandidate>
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GVNSink::analyzeInstructionForSinking(LockstepReverseIterator &LRI,
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GVNSink::analyzeInstructionForSinking(LockstepReverseIterator<false> &LRI,
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unsigned &InstNum,
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unsigned &MemoryInstNum,
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ModelledPHISet &NeededPHIs,
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return BB->getTerminator()->getNumSuccessors() != 1;
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});
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830-
LockstepReverseIterator LRI(Preds);
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LockstepReverseIterator<false> LRI(Preds);
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SmallVector<SinkingInstructionCandidate, 4> Candidates;
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unsigned InstNum = 0, MemoryInstNum = 0;
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ModelledPHISet NeededPHIs;

‎llvm/lib/Transforms/Utils/SimplifyCFG.cpp

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@@ -74,6 +74,7 @@
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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/Local.h"
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#include "llvm/Transforms/Utils/LockstepReverseIterator.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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#include <algorithm>
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#include <cassert>
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25002501
int ScanIdx = 0;
25012502
SmallPtrSet<Value*,4> InstructionsToSink;
2502-
LockstepReverseIterator LRI(UnconditionalPreds);
2503+
LockstepReverseIterator<true> LRI(UnconditionalPreds);
25032504
while (LRI.isValid() &&
25042505
canSinkInstructions(*LRI, PHIOperands)) {
25052506
LLVM_DEBUG(dbgs() << "SINK: instruction can be sunk: " << *(*LRI)[0]
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25292530
// Okay, we *could* sink last ScanIdx instructions. But how many can we
25302531
// actually sink before encountering instruction that is unprofitable to
25312532
// sink?
2532-
auto ProfitableToSinkInstruction = [&](LockstepReverseIterator &LRI) {
2533+
auto ProfitableToSinkInstruction = [&](LockstepReverseIterator<true> &LRI) {
25332534
unsigned NumPHIInsts = 0;
25342535
for (Use &U : (*LRI)[0]->operands()) {
25352536
auto It = PHIOperands.find(&U);

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