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//===- SROA.h - Scalar Replacement Of Aggregates ----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file provides the interface for LLVM's Scalar Replacement of
/// Aggregates pass. This pass provides both aggregate splitting and the
/// primary SSA formation used in the compiler.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_SROA_H
#define LLVM_TRANSFORMS_SCALAR_SROA_H
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/ValueHandle.h"
#include <vector>
namespace llvm {
class AllocaInst;
class AssumptionCache;
class DominatorTree;
class Function;
class Instruction;
class LLVMContext;
class PHINode;
class SelectInst;
class Use;
/// A private "module" namespace for types and utilities used by SROA. These
/// are implementation details and should not be used by clients.
namespace sroa LLVM_LIBRARY_VISIBILITY {
class AllocaSliceRewriter;
class AllocaSlices;
class Partition;
class SROALegacyPass;
} // end namespace sroa
/// An optimization pass providing Scalar Replacement of Aggregates.
///
/// This pass takes allocations which can be completely analyzed (that is, they
/// don't escape) and tries to turn them into scalar SSA values. There are
/// a few steps to this process.
///
/// 1) It takes allocations of aggregates and analyzes the ways in which they
/// are used to try to split them into smaller allocations, ideally of
/// a single scalar data type. It will split up memcpy and memset accesses
/// as necessary and try to isolate individual scalar accesses.
/// 2) It will transform accesses into forms which are suitable for SSA value
/// promotion. This can be replacing a memset with a scalar store of an
/// integer value, or it can involve speculating operations on a PHI or
/// select to be a PHI or select of the results.
/// 3) Finally, this will try to detect a pattern of accesses which map cleanly
/// onto insert and extract operations on a vector value, and convert them to
/// this form. By doing so, it will enable promotion of vector aggregates to
/// SSA vector values.
class SROAPass : public PassInfoMixin<SROAPass> {
LLVMContext *C = nullptr;
DominatorTree *DT = nullptr;
AssumptionCache *AC = nullptr;
/// Worklist of alloca instructions to simplify.
///
/// Each alloca in the function is added to this. Each new alloca formed gets
/// added to it as well to recursively simplify unless that alloca can be
/// directly promoted. Finally, each time we rewrite a use of an alloca other
/// the one being actively rewritten, we add it back onto the list if not
/// already present to ensure it is re-visited.
SetVector<AllocaInst *, SmallVector<AllocaInst *, 16>> Worklist;
/// A collection of instructions to delete.
/// We try to batch deletions to simplify code and make things a bit more
/// efficient. We also make sure there is no dangling pointers.
SmallVector<WeakVH, 8> DeadInsts;
/// Post-promotion worklist.
///
/// Sometimes we discover an alloca which has a high probability of becoming
/// viable for SROA after a round of promotion takes place. In those cases,
/// the alloca is enqueued here for re-processing.
///
/// Note that we have to be very careful to clear allocas out of this list in
/// the event they are deleted.
SetVector<AllocaInst *, SmallVector<AllocaInst *, 16>> PostPromotionWorklist;
/// A collection of alloca instructions we can directly promote.
std::vector<AllocaInst *> PromotableAllocas;
/// A worklist of PHIs to speculate prior to promoting allocas.
///
/// All of these PHIs have been checked for the safety of speculation and by
/// being speculated will allow promoting allocas currently in the promotable
/// queue.
SetVector<PHINode *, SmallVector<PHINode *, 2>> SpeculatablePHIs;
/// A worklist of select instructions to speculate prior to promoting
/// allocas.
///
/// All of these select instructions have been checked for the safety of
/// speculation and by being speculated will allow promoting allocas
/// currently in the promotable queue.
SetVector<SelectInst *, SmallVector<SelectInst *, 2>> SpeculatableSelects;
public:
SROAPass() = default;
/// Run the pass over the function.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
private:
friend class sroa::AllocaSliceRewriter;
friend class sroa::SROALegacyPass;
/// Helper used by both the public run method and by the legacy pass.
PreservedAnalyses runImpl(Function &F, DominatorTree &RunDT,
AssumptionCache &RunAC);
bool presplitLoadsAndStores(AllocaInst &AI, sroa::AllocaSlices &AS);
AllocaInst *rewritePartition(AllocaInst &AI, sroa::AllocaSlices &AS,
sroa::Partition &P);
bool splitAlloca(AllocaInst &AI, sroa::AllocaSlices &AS);
bool runOnAlloca(AllocaInst &AI);
void clobberUse(Use &U);
bool deleteDeadInstructions(SmallPtrSetImpl<AllocaInst *> &DeletedAllocas);
bool promoteAllocas(Function &F);
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_SCALAR_SROA_H
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