| //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements sparse conditional constant propagation and merging: |
| // |
| // Specifically, this: |
| // * Assumes values are constant unless proven otherwise |
| // * Assumes BasicBlocks are dead unless proven otherwise |
| // * Proves values to be constant, and replaces them with constants |
| // * Proves conditional branches to be unconditional |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar/SCCP.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/MapVector.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/DomTreeUpdater.h" |
| #include "llvm/Analysis/GlobalsModRef.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/Constant.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/GlobalVariable.h" |
| #include "llvm/IR/InstrTypes.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/PassManager.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/SCCPSolver.h" |
| #include <cassert> |
| #include <utility> |
| #include <vector> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "sccp" |
| |
| STATISTIC(NumInstRemoved, "Number of instructions removed"); |
| STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable"); |
| STATISTIC(NumInstReplaced, |
| "Number of instructions replaced with (simpler) instruction"); |
| |
| // runSCCP() - Run the Sparse Conditional Constant Propagation algorithm, |
| // and return true if the function was modified. |
| static bool runSCCP(Function &F, const DataLayout &DL, |
| const TargetLibraryInfo *TLI, DomTreeUpdater &DTU) { |
| LLVM_DEBUG(dbgs() << "SCCP on function '" << F.getName() << "'\n"); |
| SCCPSolver Solver( |
| DL, [TLI](Function &F) -> const TargetLibraryInfo & { return *TLI; }, |
| F.getContext()); |
| |
| // Mark the first block of the function as being executable. |
| Solver.markBlockExecutable(&F.front()); |
| |
| // Mark all arguments to the function as being overdefined. |
| for (Argument &AI : F.args()) |
| Solver.markOverdefined(&AI); |
| |
| // Solve for constants. |
| bool ResolvedUndefs = true; |
| while (ResolvedUndefs) { |
| Solver.solve(); |
| LLVM_DEBUG(dbgs() << "RESOLVING UNDEFs\n"); |
| ResolvedUndefs = Solver.resolvedUndefsIn(F); |
| } |
| |
| bool MadeChanges = false; |
| |
| // If we decided that there are basic blocks that are dead in this function, |
| // delete their contents now. Note that we cannot actually delete the blocks, |
| // as we cannot modify the CFG of the function. |
| |
| SmallPtrSet<Value *, 32> InsertedValues; |
| SmallVector<BasicBlock *, 8> BlocksToErase; |
| for (BasicBlock &BB : F) { |
| if (!Solver.isBlockExecutable(&BB)) { |
| LLVM_DEBUG(dbgs() << " BasicBlock Dead:" << BB); |
| ++NumDeadBlocks; |
| BlocksToErase.push_back(&BB); |
| MadeChanges = true; |
| continue; |
| } |
| |
| MadeChanges |= Solver.simplifyInstsInBlock(BB, InsertedValues, |
| NumInstRemoved, NumInstReplaced); |
| } |
| |
| // Remove unreachable blocks and non-feasible edges. |
| for (BasicBlock *DeadBB : BlocksToErase) |
| NumInstRemoved += changeToUnreachable(DeadBB->getFirstNonPHI(), |
| /*PreserveLCSSA=*/false, &DTU); |
| |
| BasicBlock *NewUnreachableBB = nullptr; |
| for (BasicBlock &BB : F) |
| MadeChanges |= Solver.removeNonFeasibleEdges(&BB, DTU, NewUnreachableBB); |
| |
| for (BasicBlock *DeadBB : BlocksToErase) |
| if (!DeadBB->hasAddressTaken()) |
| DTU.deleteBB(DeadBB); |
| |
| return MadeChanges; |
| } |
| |
| PreservedAnalyses SCCPPass::run(Function &F, FunctionAnalysisManager &AM) { |
| const DataLayout &DL = F.getParent()->getDataLayout(); |
| auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); |
| auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F); |
| DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy); |
| if (!runSCCP(F, DL, &TLI, DTU)) |
| return PreservedAnalyses::all(); |
| |
| auto PA = PreservedAnalyses(); |
| PA.preserve<DominatorTreeAnalysis>(); |
| return PA; |
| } |