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14b0529532
Add support for specifying alignment and size of setjmp jmpbufs. No targets currently do anything with this information, nor is it presrved in the bytecode representation. That's coming up next. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24196 91177308-0d34-0410-b5e6-96231b3b80d8
381 lines
14 KiB
C++
381 lines
14 KiB
C++
//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This transformation implements the well known scalar replacement of
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// aggregates transformation. This xform breaks up alloca instructions of
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// aggregate type (structure or array) into individual alloca instructions for
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// each member (if possible). Then, if possible, it transforms the individual
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// alloca instructions into nice clean scalar SSA form.
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//
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// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
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// often interact, especially for C++ programs. As such, iterating between
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// SRoA, then Mem2Reg until we run out of things to promote works well.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/Pass.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/PromoteMemToReg.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringExtras.h"
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using namespace llvm;
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namespace {
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Statistic<> NumReplaced("scalarrepl", "Number of allocas broken up");
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Statistic<> NumPromoted("scalarrepl", "Number of allocas promoted");
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struct SROA : public FunctionPass {
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bool runOnFunction(Function &F);
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bool performScalarRepl(Function &F);
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bool performPromotion(Function &F);
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// getAnalysisUsage - This pass does not require any passes, but we know it
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// will not alter the CFG, so say so.
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<DominatorTree>();
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AU.addRequired<DominanceFrontier>();
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AU.addRequired<TargetData>();
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AU.setPreservesCFG();
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}
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private:
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int isSafeElementUse(Value *Ptr);
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int isSafeUseOfAllocation(Instruction *User);
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int isSafeAllocaToScalarRepl(AllocationInst *AI);
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void CanonicalizeAllocaUsers(AllocationInst *AI);
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AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base);
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};
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RegisterOpt<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
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}
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// Public interface to the ScalarReplAggregates pass
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FunctionPass *llvm::createScalarReplAggregatesPass() { return new SROA(); }
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bool SROA::runOnFunction(Function &F) {
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bool Changed = performPromotion(F);
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while (1) {
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bool LocalChange = performScalarRepl(F);
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if (!LocalChange) break; // No need to repromote if no scalarrepl
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Changed = true;
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LocalChange = performPromotion(F);
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if (!LocalChange) break; // No need to re-scalarrepl if no promotion
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}
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return Changed;
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}
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bool SROA::performPromotion(Function &F) {
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std::vector<AllocaInst*> Allocas;
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const TargetData &TD = getAnalysis<TargetData>();
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DominatorTree &DT = getAnalysis<DominatorTree>();
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DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
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BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
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bool Changed = false;
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while (1) {
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Allocas.clear();
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// Find allocas that are safe to promote, by looking at all instructions in
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// the entry node
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for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
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if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
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if (isAllocaPromotable(AI, TD))
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Allocas.push_back(AI);
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if (Allocas.empty()) break;
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PromoteMemToReg(Allocas, DT, DF, TD);
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NumPromoted += Allocas.size();
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Changed = true;
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}
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return Changed;
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}
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// performScalarRepl - This algorithm is a simple worklist driven algorithm,
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// which runs on all of the malloc/alloca instructions in the function, removing
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// them if they are only used by getelementptr instructions.
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//
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bool SROA::performScalarRepl(Function &F) {
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std::vector<AllocationInst*> WorkList;
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// Scan the entry basic block, adding any alloca's and mallocs to the worklist
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BasicBlock &BB = F.getEntryBlock();
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for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
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if (AllocationInst *A = dyn_cast<AllocationInst>(I))
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WorkList.push_back(A);
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// Process the worklist
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bool Changed = false;
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while (!WorkList.empty()) {
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AllocationInst *AI = WorkList.back();
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WorkList.pop_back();
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// We cannot transform the allocation instruction if it is an array
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// allocation (allocations OF arrays are ok though), and an allocation of a
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// scalar value cannot be decomposed at all.
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//
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if (AI->isArrayAllocation() ||
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(!isa<StructType>(AI->getAllocatedType()) &&
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!isa<ArrayType>(AI->getAllocatedType()))) continue;
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// Check that all of the users of the allocation are capable of being
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// transformed.
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switch (isSafeAllocaToScalarRepl(AI)) {
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default: assert(0 && "Unexpected value!");
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case 0: // Not safe to scalar replace.
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continue;
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case 1: // Safe, but requires cleanup/canonicalizations first
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CanonicalizeAllocaUsers(AI);
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case 3: // Safe to scalar replace.
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break;
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}
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DEBUG(std::cerr << "Found inst to xform: " << *AI);
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Changed = true;
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std::vector<AllocaInst*> ElementAllocas;
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if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
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ElementAllocas.reserve(ST->getNumContainedTypes());
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for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
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AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
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AI->getAlignment(),
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AI->getName() + "." + utostr(i), AI);
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ElementAllocas.push_back(NA);
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WorkList.push_back(NA); // Add to worklist for recursive processing
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}
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} else {
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const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
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ElementAllocas.reserve(AT->getNumElements());
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const Type *ElTy = AT->getElementType();
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for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
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AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
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AI->getName() + "." + utostr(i), AI);
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ElementAllocas.push_back(NA);
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WorkList.push_back(NA); // Add to worklist for recursive processing
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}
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}
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// Now that we have created the alloca instructions that we want to use,
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// expand the getelementptr instructions to use them.
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//
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while (!AI->use_empty()) {
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Instruction *User = cast<Instruction>(AI->use_back());
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GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
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// We now know that the GEP is of the form: GEP <ptr>, 0, <cst>
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unsigned Idx =
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(unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getRawValue();
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assert(Idx < ElementAllocas.size() && "Index out of range?");
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AllocaInst *AllocaToUse = ElementAllocas[Idx];
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Value *RepValue;
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if (GEPI->getNumOperands() == 3) {
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// Do not insert a new getelementptr instruction with zero indices, only
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// to have it optimized out later.
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RepValue = AllocaToUse;
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} else {
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// We are indexing deeply into the structure, so we still need a
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// getelement ptr instruction to finish the indexing. This may be
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// expanded itself once the worklist is rerun.
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//
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std::string OldName = GEPI->getName(); // Steal the old name.
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std::vector<Value*> NewArgs;
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NewArgs.push_back(Constant::getNullValue(Type::IntTy));
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NewArgs.insert(NewArgs.end(), GEPI->op_begin()+3, GEPI->op_end());
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GEPI->setName("");
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RepValue = new GetElementPtrInst(AllocaToUse, NewArgs, OldName, GEPI);
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}
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// Move all of the users over to the new GEP.
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GEPI->replaceAllUsesWith(RepValue);
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// Delete the old GEP
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GEPI->eraseFromParent();
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}
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// Finally, delete the Alloca instruction
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AI->getParent()->getInstList().erase(AI);
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NumReplaced++;
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}
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return Changed;
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}
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/// isSafeElementUse - Check to see if this use is an allowed use for a
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/// getelementptr instruction of an array aggregate allocation.
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///
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int SROA::isSafeElementUse(Value *Ptr) {
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for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
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I != E; ++I) {
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Instruction *User = cast<Instruction>(*I);
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switch (User->getOpcode()) {
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case Instruction::Load: break;
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case Instruction::Store:
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// Store is ok if storing INTO the pointer, not storing the pointer
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if (User->getOperand(0) == Ptr) return 0;
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break;
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case Instruction::GetElementPtr: {
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GetElementPtrInst *GEP = cast<GetElementPtrInst>(User);
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if (GEP->getNumOperands() > 1) {
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if (!isa<Constant>(GEP->getOperand(1)) ||
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!cast<Constant>(GEP->getOperand(1))->isNullValue())
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return 0; // Using pointer arithmetic to navigate the array...
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}
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if (!isSafeElementUse(GEP)) return 0;
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break;
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}
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default:
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DEBUG(std::cerr << " Transformation preventing inst: " << *User);
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return 0;
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}
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}
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return 3; // All users look ok :)
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}
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/// AllUsersAreLoads - Return true if all users of this value are loads.
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static bool AllUsersAreLoads(Value *Ptr) {
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for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
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I != E; ++I)
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if (cast<Instruction>(*I)->getOpcode() != Instruction::Load)
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return false;
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return true;
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}
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/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an
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/// aggregate allocation.
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///
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int SROA::isSafeUseOfAllocation(Instruction *User) {
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if (!isa<GetElementPtrInst>(User)) return 0;
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GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
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gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI);
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// The GEP is safe to transform if it is of the form GEP <ptr>, 0, <cst>
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if (I == E ||
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I.getOperand() != Constant::getNullValue(I.getOperand()->getType()))
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return 0;
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++I;
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if (I == E) return 0; // ran out of GEP indices??
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// If this is a use of an array allocation, do a bit more checking for sanity.
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if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
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uint64_t NumElements = AT->getNumElements();
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if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
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// Check to make sure that index falls within the array. If not,
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// something funny is going on, so we won't do the optimization.
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//
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if (cast<ConstantInt>(GEPI->getOperand(2))->getRawValue() >= NumElements)
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return 0;
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} else {
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// If this is an array index and the index is not constant, we cannot
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// promote... that is unless the array has exactly one or two elements in
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// it, in which case we CAN promote it, but we have to canonicalize this
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// out if this is the only problem.
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if (NumElements == 1 || NumElements == 2)
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return AllUsersAreLoads(GEPI) ? 1 : 0; // Canonicalization required!
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return 0;
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}
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}
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// If there are any non-simple uses of this getelementptr, make sure to reject
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// them.
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return isSafeElementUse(GEPI);
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}
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/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
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/// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
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/// or 1 if safe after canonicalization has been performed.
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///
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int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) {
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// Loop over the use list of the alloca. We can only transform it if all of
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// the users are safe to transform.
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//
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int isSafe = 3;
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for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
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I != E; ++I) {
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isSafe &= isSafeUseOfAllocation(cast<Instruction>(*I));
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if (isSafe == 0) {
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DEBUG(std::cerr << "Cannot transform: " << *AI << " due to user: "
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<< **I);
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return 0;
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}
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}
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// If we require cleanup, isSafe is now 1, otherwise it is 3.
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return isSafe;
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}
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/// CanonicalizeAllocaUsers - If SROA reported that it can promote the specified
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/// allocation, but only if cleaned up, perform the cleanups required.
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void SROA::CanonicalizeAllocaUsers(AllocationInst *AI) {
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// At this point, we know that the end result will be SROA'd and promoted, so
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// we can insert ugly code if required so long as sroa+mem2reg will clean it
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// up.
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for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
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UI != E; ) {
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GetElementPtrInst *GEPI = cast<GetElementPtrInst>(*UI++);
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gep_type_iterator I = gep_type_begin(GEPI);
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++I;
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if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
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uint64_t NumElements = AT->getNumElements();
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if (!isa<ConstantInt>(I.getOperand())) {
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if (NumElements == 1) {
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GEPI->setOperand(2, Constant::getNullValue(Type::IntTy));
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} else {
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assert(NumElements == 2 && "Unhandled case!");
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// All users of the GEP must be loads. At each use of the GEP, insert
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// two loads of the appropriate indexed GEP and select between them.
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Value *IsOne = BinaryOperator::createSetNE(I.getOperand(),
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Constant::getNullValue(I.getOperand()->getType()),
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"isone", GEPI);
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// Insert the new GEP instructions, which are properly indexed.
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std::vector<Value*> Indices(GEPI->op_begin()+1, GEPI->op_end());
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Indices[1] = Constant::getNullValue(Type::IntTy);
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Value *ZeroIdx = new GetElementPtrInst(GEPI->getOperand(0), Indices,
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GEPI->getName()+".0", GEPI);
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Indices[1] = ConstantInt::get(Type::IntTy, 1);
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Value *OneIdx = new GetElementPtrInst(GEPI->getOperand(0), Indices,
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GEPI->getName()+".1", GEPI);
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// Replace all loads of the variable index GEP with loads from both
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// indexes and a select.
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while (!GEPI->use_empty()) {
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LoadInst *LI = cast<LoadInst>(GEPI->use_back());
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Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI);
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Value *One = new LoadInst(OneIdx , LI->getName()+".1", LI);
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Value *R = new SelectInst(IsOne, One, Zero, LI->getName(), LI);
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LI->replaceAllUsesWith(R);
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LI->eraseFromParent();
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}
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GEPI->eraseFromParent();
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}
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}
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}
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}
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}
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