mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-19 19:29:31 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4935 91177308-0d34-0410-b5e6-96231b3b80d8
841 lines
31 KiB
C++
841 lines
31 KiB
C++
//===- InstructionCombining.cpp - Combine multiple instructions -----------===//
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//
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// InstructionCombining - Combine instructions to form fewer, simple
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// instructions. This pass does not modify the CFG This pass is where algebraic
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// simplification happens.
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//
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// This pass combines things like:
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// %Y = add int 1, %X
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// %Z = add int 1, %Y
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// into:
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// %Z = add int 2, %X
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//
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// This is a simple worklist driven algorithm.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.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/ConstantHandling.h"
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#include "llvm/iMemory.h"
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#include "llvm/iOther.h"
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#include "llvm/iPHINode.h"
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#include "llvm/iOperators.h"
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#include "llvm/Pass.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/Support/InstVisitor.h"
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#include "Support/Statistic.h"
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#include <algorithm>
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namespace {
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Statistic<> NumCombined ("instcombine", "Number of insts combined");
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Statistic<> NumConstProp("instcombine", "Number of constant folds");
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Statistic<> NumDeadInst ("instcombine", "Number of dead inst eliminated");
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class InstCombiner : public FunctionPass,
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public InstVisitor<InstCombiner, Instruction*> {
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// Worklist of all of the instructions that need to be simplified.
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std::vector<Instruction*> WorkList;
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void AddUsesToWorkList(Instruction &I) {
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// The instruction was simplified, add all users of the instruction to
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// the work lists because they might get more simplified now...
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//
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for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
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UI != UE; ++UI)
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WorkList.push_back(cast<Instruction>(*UI));
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}
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// removeFromWorkList - remove all instances of I from the worklist.
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void removeFromWorkList(Instruction *I);
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public:
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virtual bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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}
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// Visitation implementation - Implement instruction combining for different
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// instruction types. The semantics are as follows:
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// Return Value:
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// null - No change was made
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// I - Change was made, I is still valid, I may be dead though
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// otherwise - Change was made, replace I with returned instruction
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//
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Instruction *visitAdd(BinaryOperator &I);
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Instruction *visitSub(BinaryOperator &I);
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Instruction *visitMul(BinaryOperator &I);
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Instruction *visitDiv(BinaryOperator &I);
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Instruction *visitRem(BinaryOperator &I);
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Instruction *visitAnd(BinaryOperator &I);
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Instruction *visitOr (BinaryOperator &I);
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Instruction *visitXor(BinaryOperator &I);
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Instruction *visitSetCondInst(BinaryOperator &I);
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Instruction *visitShiftInst(Instruction &I);
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Instruction *visitCastInst(CastInst &CI);
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Instruction *visitPHINode(PHINode &PN);
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Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
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Instruction *visitAllocationInst(AllocationInst &AI);
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// visitInstruction - Specify what to return for unhandled instructions...
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Instruction *visitInstruction(Instruction &I) { return 0; }
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// InsertNewInstBefore - insert an instruction New before instruction Old
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// in the program. Add the new instruction to the worklist.
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//
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void InsertNewInstBefore(Instruction *New, Instruction &Old) {
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assert(New && New->getParent() == 0 &&
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"New instruction already inserted into a basic block!");
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BasicBlock *BB = Old.getParent();
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BB->getInstList().insert(&Old, New); // Insert inst
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WorkList.push_back(New); // Add to worklist
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}
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// ReplaceInstUsesWith - This method is to be used when an instruction is
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// found to be dead, replacable with another preexisting expression. Here
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// we add all uses of I to the worklist, replace all uses of I with the new
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// value, then return I, so that the inst combiner will know that I was
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// modified.
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//
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Instruction *ReplaceInstUsesWith(Instruction &I, Value *V) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I.replaceAllUsesWith(V);
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return &I;
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}
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};
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RegisterOpt<InstCombiner> X("instcombine", "Combine redundant instructions");
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}
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// Make sure that this instruction has a constant on the right hand side if it
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// has any constant arguments. If not, fix it an return true.
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//
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static bool SimplifyBinOp(BinaryOperator &I) {
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if (isa<Constant>(I.getOperand(0)) && !isa<Constant>(I.getOperand(1)))
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return !I.swapOperands();
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return false;
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}
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// dyn_castNegInst - Given a 'sub' instruction, return the RHS of the
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// instruction if the LHS is a constant zero (which is the 'negate' form).
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//
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static inline Value *dyn_castNegInst(Value *V) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I || I->getOpcode() != Instruction::Sub) return 0;
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if (I->getOperand(0) == Constant::getNullValue(I->getType()))
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return I->getOperand(1);
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return 0;
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}
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static inline Value *dyn_castNotInst(Value *V) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I || I->getOpcode() != Instruction::Xor) return 0;
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if (ConstantIntegral *CI = dyn_cast<ConstantIntegral>(I->getOperand(1)))
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if (CI->isAllOnesValue())
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return I->getOperand(0);
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return 0;
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}
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Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
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// Eliminate 'add int %X, 0'
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if (RHS == Constant::getNullValue(I.getType()))
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return ReplaceInstUsesWith(I, LHS);
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// -A + B --> B - A
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if (Value *V = dyn_castNegInst(LHS))
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return BinaryOperator::create(Instruction::Sub, RHS, V);
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// A + -B --> A - B
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if (Value *V = dyn_castNegInst(RHS))
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return BinaryOperator::create(Instruction::Sub, LHS, V);
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// Simplify add instructions with a constant RHS...
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if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
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if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
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if (ILHS->getOpcode() == Instruction::Add &&
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isa<Constant>(ILHS->getOperand(1))) {
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// Fold:
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// %Y = add int %X, 1
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// %Z = add int %Y, 1
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// into:
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// %Z = add int %X, 2
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//
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if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
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I.setOperand(0, ILHS->getOperand(0));
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I.setOperand(1, Val);
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return &I;
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}
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}
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}
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}
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return Changed ? &I : 0;
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}
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Instruction *InstCombiner::visitSub(BinaryOperator &I) {
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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if (Op0 == Op1) // sub X, X -> 0
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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// If this is a subtract instruction with a constant RHS, convert it to an add
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// instruction of a negative constant
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//
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if (Constant *Op2 = dyn_cast<Constant>(Op1))
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if (Constant *RHS = *Constant::getNullValue(I.getType()) - *Op2) // 0 - RHS
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return BinaryOperator::create(Instruction::Add, Op0, RHS, I.getName());
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// If this is a 'B = x-(-A)', change to B = x+A...
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if (Value *V = dyn_castNegInst(Op1))
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return BinaryOperator::create(Instruction::Add, Op0, V);
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// Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression is
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// not used by anyone else...
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//
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if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
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if (Op1I->use_size() == 1 && Op1I->getOpcode() == Instruction::Sub) {
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// Swap the two operands of the subexpr...
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Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
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Op1I->setOperand(0, IIOp1);
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Op1I->setOperand(1, IIOp0);
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// Create the new top level add instruction...
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return BinaryOperator::create(Instruction::Add, Op0, Op1);
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}
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return 0;
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}
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Instruction *InstCombiner::visitMul(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *Op1 = I.getOperand(0);
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// Simplify mul instructions with a constant RHS...
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if (Constant *Op2 = dyn_cast<Constant>(I.getOperand(1))) {
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if (I.getType()->isInteger() && cast<ConstantInt>(Op2)->equalsInt(1))
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return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul int %X, 1'
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if (I.getType()->isInteger() && cast<ConstantInt>(Op2)->equalsInt(2))
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// Convert 'mul int %X, 2' to 'add int %X, %X'
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return BinaryOperator::create(Instruction::Add, Op1, Op1, I.getName());
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if (Op2->isNullValue())
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return ReplaceInstUsesWith(I, Op2); // Eliminate 'mul int %X, 0'
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}
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return Changed ? &I : 0;
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}
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Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
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// div X, 1 == X
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if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1)))
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if (RHS->equalsInt(1))
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return ReplaceInstUsesWith(I, I.getOperand(0));
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return 0;
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}
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Instruction *InstCombiner::visitRem(BinaryOperator &I) {
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// rem X, 1 == 0
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if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1)))
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if (RHS->equalsInt(1))
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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return 0;
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}
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// isMaxValueMinusOne - return true if this is Max-1
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static bool isMaxValueMinusOne(const ConstantInt *C) {
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if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
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// Calculate -1 casted to the right type...
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unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
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uint64_t Val = ~0ULL; // All ones
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Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
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return CU->getValue() == Val-1;
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}
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const ConstantSInt *CS = cast<ConstantSInt>(C);
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// Calculate 0111111111..11111
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unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
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int64_t Val = INT64_MAX; // All ones
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Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
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return CS->getValue() == Val-1;
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}
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// isMinValuePlusOne - return true if this is Min+1
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static bool isMinValuePlusOne(const ConstantInt *C) {
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if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
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return CU->getValue() == 1;
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const ConstantSInt *CS = cast<ConstantSInt>(C);
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// Calculate 1111111111000000000000
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unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
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int64_t Val = -1; // All ones
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Val <<= TypeBits-1; // Shift over to the right spot
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return CS->getValue() == Val+1;
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}
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Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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// and X, X = X and X, 0 == 0
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if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
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return ReplaceInstUsesWith(I, Op1);
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// and X, -1 == X
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if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
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if (RHS->isAllOnesValue())
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return ReplaceInstUsesWith(I, Op0);
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// and (not A), (not B) == not (or A, B)
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if (Op0->use_size() == 1 && Op1->use_size() == 1)
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if (Value *A = dyn_castNotInst(Op0))
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if (Value *B = dyn_castNotInst(Op1)) {
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Instruction *Or = BinaryOperator::create(Instruction::Or, A, B,
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I.getName()+".demorgan");
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InsertNewInstBefore(Or, I);
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return BinaryOperator::createNot(Or, I.getName());
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}
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return Changed ? &I : 0;
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}
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Instruction *InstCombiner::visitOr(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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// or X, X = X or X, 0 == X
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if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
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return ReplaceInstUsesWith(I, Op0);
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// or X, -1 == -1
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if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
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if (RHS->isAllOnesValue())
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return ReplaceInstUsesWith(I, Op1);
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return Changed ? &I : 0;
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}
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Instruction *InstCombiner::visitXor(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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// xor X, X = 0
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if (Op0 == Op1)
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
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// xor X, 0 == X
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if (Op1C->isNullValue())
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return ReplaceInstUsesWith(I, Op0);
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// Is this a "NOT" instruction?
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if (Op1C->isAllOnesValue()) {
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// xor (xor X, -1), -1 = not (not X) = X
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if (Value *X = dyn_castNotInst(Op0))
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return ReplaceInstUsesWith(I, X);
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// xor (setcc A, B), true = not (setcc A, B) = setncc A, B
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if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
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if (SCI->use_size() == 1)
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return new SetCondInst(SCI->getInverseCondition(),
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SCI->getOperand(0), SCI->getOperand(1));
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}
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}
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return Changed ? &I : 0;
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}
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// AddOne, SubOne - Add or subtract a constant one from an integer constant...
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static Constant *AddOne(ConstantInt *C) {
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Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
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assert(Result && "Constant folding integer addition failed!");
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return Result;
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}
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static Constant *SubOne(ConstantInt *C) {
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Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
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assert(Result && "Constant folding integer addition failed!");
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return Result;
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}
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// isTrueWhenEqual - Return true if the specified setcondinst instruction is
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// true when both operands are equal...
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//
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static bool isTrueWhenEqual(Instruction &I) {
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return I.getOpcode() == Instruction::SetEQ ||
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I.getOpcode() == Instruction::SetGE ||
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I.getOpcode() == Instruction::SetLE;
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}
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Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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const Type *Ty = Op0->getType();
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// setcc X, X
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if (Op0 == Op1)
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return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
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// setcc <global*>, 0 - Global value addresses are never null!
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if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
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return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
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// setcc's with boolean values can always be turned into bitwise operations
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if (Ty == Type::BoolTy) {
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// If this is <, >, or !=, we can change this into a simple xor instruction
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if (!isTrueWhenEqual(I))
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return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
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// Otherwise we need to make a temporary intermediate instruction and insert
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// it into the instruction stream. This is what we are after:
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//
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// seteq bool %A, %B -> ~(A^B)
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// setle bool %A, %B -> ~A | B
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// setge bool %A, %B -> A | ~B
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//
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if (I.getOpcode() == Instruction::SetEQ) { // seteq case
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Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
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I.getName()+"tmp");
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InsertNewInstBefore(Xor, I);
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return BinaryOperator::createNot(Xor, I.getName());
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}
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// Handle the setXe cases...
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assert(I.getOpcode() == Instruction::SetGE ||
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I.getOpcode() == Instruction::SetLE);
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if (I.getOpcode() == Instruction::SetGE)
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std::swap(Op0, Op1); // Change setge -> setle
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// Now we just have the SetLE case.
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Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
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InsertNewInstBefore(Not, I);
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return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
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}
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// Check to see if we are doing one of many comparisons against constant
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// integers at the end of their ranges...
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//
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if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
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// Check to see if we are comparing against the minimum or maximum value...
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if (CI->isMinValue()) {
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if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
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return ReplaceInstUsesWith(I, ConstantBool::False);
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if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
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return ReplaceInstUsesWith(I, ConstantBool::True);
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if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
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return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
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if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
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return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
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} else if (CI->isMaxValue()) {
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if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
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return ReplaceInstUsesWith(I, ConstantBool::False);
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if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
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return ReplaceInstUsesWith(I, ConstantBool::True);
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if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
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return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
|
|
if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
|
|
return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
|
|
|
|
// Comparing against a value really close to min or max?
|
|
} else if (isMinValuePlusOne(CI)) {
|
|
if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
|
|
return BinaryOperator::create(Instruction::SetEQ, Op0,
|
|
SubOne(CI), I.getName());
|
|
if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
|
|
return BinaryOperator::create(Instruction::SetNE, Op0,
|
|
SubOne(CI), I.getName());
|
|
|
|
} else if (isMaxValueMinusOne(CI)) {
|
|
if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
|
|
return BinaryOperator::create(Instruction::SetEQ, Op0,
|
|
AddOne(CI), I.getName());
|
|
if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
|
|
return BinaryOperator::create(Instruction::SetNE, Op0,
|
|
AddOne(CI), I.getName());
|
|
}
|
|
}
|
|
|
|
return Changed ? &I : 0;
|
|
}
|
|
|
|
|
|
|
|
Instruction *InstCombiner::visitShiftInst(Instruction &I) {
|
|
assert(I.getOperand(1)->getType() == Type::UByteTy);
|
|
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
|
|
|
|
// shl X, 0 == X and shr X, 0 == X
|
|
// shl 0, X == 0 and shr 0, X == 0
|
|
if (Op1 == Constant::getNullValue(Type::UByteTy) ||
|
|
Op0 == Constant::getNullValue(Op0->getType()))
|
|
return ReplaceInstUsesWith(I, Op0);
|
|
|
|
// shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
|
|
// a signed value.
|
|
//
|
|
if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
|
|
if (I.getOpcode() == Instruction::Shr) {
|
|
unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
|
|
if (CUI->getValue() >= TypeBits && !(Op0->getType()->isSigned()))
|
|
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
|
|
}
|
|
|
|
// Check to see if we are shifting left by 1. If so, turn it into an add
|
|
// instruction.
|
|
if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
|
|
// Convert 'shl int %X, 2' to 'add int %X, %X'
|
|
return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
|
|
|
|
}
|
|
|
|
// shr int -1, X = -1 (for any arithmetic shift rights of ~0)
|
|
if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
|
|
if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
|
|
return ReplaceInstUsesWith(I, CSI);
|
|
|
|
return 0;
|
|
}
|
|
|
|
|
|
// isEliminableCastOfCast - Return true if it is valid to eliminate the CI
|
|
// instruction.
|
|
//
|
|
static inline bool isEliminableCastOfCast(const CastInst &CI,
|
|
const CastInst *CSrc) {
|
|
assert(CI.getOperand(0) == CSrc);
|
|
const Type *SrcTy = CSrc->getOperand(0)->getType();
|
|
const Type *MidTy = CSrc->getType();
|
|
const Type *DstTy = CI.getType();
|
|
|
|
// It is legal to eliminate the instruction if casting A->B->A if the sizes
|
|
// are identical and the bits don't get reinterpreted (for example
|
|
// int->float->int would not be allowed)
|
|
if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
|
|
return true;
|
|
|
|
// Allow free casting and conversion of sizes as long as the sign doesn't
|
|
// change...
|
|
if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
|
|
unsigned SrcSize = SrcTy->getPrimitiveSize();
|
|
unsigned MidSize = MidTy->getPrimitiveSize();
|
|
unsigned DstSize = DstTy->getPrimitiveSize();
|
|
|
|
// Cases where we are monotonically decreasing the size of the type are
|
|
// always ok, regardless of what sign changes are going on.
|
|
//
|
|
if (SrcSize >= MidSize && MidSize >= DstSize)
|
|
return true;
|
|
|
|
// Cases where the source and destination type are the same, but the middle
|
|
// type is bigger are noops.
|
|
//
|
|
if (SrcSize == DstSize && MidSize > SrcSize)
|
|
return true;
|
|
|
|
// If we are monotonically growing, things are more complex.
|
|
//
|
|
if (SrcSize <= MidSize && MidSize <= DstSize) {
|
|
// We have eight combinations of signedness to worry about. Here's the
|
|
// table:
|
|
static const int SignTable[8] = {
|
|
// CODE, SrcSigned, MidSigned, DstSigned, Comment
|
|
1, // U U U Always ok
|
|
1, // U U S Always ok
|
|
3, // U S U Ok iff SrcSize != MidSize
|
|
3, // U S S Ok iff SrcSize != MidSize
|
|
0, // S U U Never ok
|
|
2, // S U S Ok iff MidSize == DstSize
|
|
1, // S S U Always ok
|
|
1, // S S S Always ok
|
|
};
|
|
|
|
// Choose an action based on the current entry of the signtable that this
|
|
// cast of cast refers to...
|
|
unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
|
|
switch (SignTable[Row]) {
|
|
case 0: return false; // Never ok
|
|
case 1: return true; // Always ok
|
|
case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
|
|
case 3: // Ok iff SrcSize != MidSize
|
|
return SrcSize != MidSize || SrcTy == Type::BoolTy;
|
|
default: assert(0 && "Bad entry in sign table!");
|
|
}
|
|
}
|
|
}
|
|
|
|
// Otherwise, we cannot succeed. Specifically we do not want to allow things
|
|
// like: short -> ushort -> uint, because this can create wrong results if
|
|
// the input short is negative!
|
|
//
|
|
return false;
|
|
}
|
|
|
|
|
|
// CastInst simplification
|
|
//
|
|
Instruction *InstCombiner::visitCastInst(CastInst &CI) {
|
|
// If the user is casting a value to the same type, eliminate this cast
|
|
// instruction...
|
|
if (CI.getType() == CI.getOperand(0)->getType())
|
|
return ReplaceInstUsesWith(CI, CI.getOperand(0));
|
|
|
|
// If casting the result of another cast instruction, try to eliminate this
|
|
// one!
|
|
//
|
|
if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
|
|
if (isEliminableCastOfCast(CI, CSrc)) {
|
|
// This instruction now refers directly to the cast's src operand. This
|
|
// has a good chance of making CSrc dead.
|
|
CI.setOperand(0, CSrc->getOperand(0));
|
|
return &CI;
|
|
}
|
|
|
|
// If this is an A->B->A cast, and we are dealing with integral types, try
|
|
// to convert this into a logical 'and' instruction.
|
|
//
|
|
if (CSrc->getOperand(0)->getType() == CI.getType() &&
|
|
CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
|
|
CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
|
|
CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
|
|
assert(CSrc->getType() != Type::ULongTy &&
|
|
"Cannot have type bigger than ulong!");
|
|
unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
|
|
Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
|
|
return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
|
|
AndOp);
|
|
}
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
|
|
// PHINode simplification
|
|
//
|
|
Instruction *InstCombiner::visitPHINode(PHINode &PN) {
|
|
// If the PHI node only has one incoming value, eliminate the PHI node...
|
|
if (PN.getNumIncomingValues() == 1)
|
|
return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
|
|
|
|
// Otherwise if all of the incoming values are the same for the PHI, replace
|
|
// the PHI node with the incoming value.
|
|
//
|
|
Value *InVal = 0;
|
|
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
|
|
if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
|
|
if (InVal && PN.getIncomingValue(i) != InVal)
|
|
return 0; // Not the same, bail out.
|
|
else
|
|
InVal = PN.getIncomingValue(i);
|
|
|
|
// The only case that could cause InVal to be null is if we have a PHI node
|
|
// that only has entries for itself. In this case, there is no entry into the
|
|
// loop, so kill the PHI.
|
|
//
|
|
if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
|
|
|
|
// All of the incoming values are the same, replace the PHI node now.
|
|
return ReplaceInstUsesWith(PN, InVal);
|
|
}
|
|
|
|
|
|
Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
|
|
// Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
|
|
// If so, eliminate the noop.
|
|
if ((GEP.getNumOperands() == 2 &&
|
|
GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
|
|
GEP.getNumOperands() == 1)
|
|
return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
|
|
|
|
// Combine Indices - If the source pointer to this getelementptr instruction
|
|
// is a getelementptr instruction, combine the indices of the two
|
|
// getelementptr instructions into a single instruction.
|
|
//
|
|
if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
|
|
std::vector<Value *> Indices;
|
|
|
|
// Can we combine the two pointer arithmetics offsets?
|
|
if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
|
|
isa<Constant>(GEP.getOperand(1))) {
|
|
// Replace the index list on this GEP with the index on the getelementptr
|
|
Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
|
|
Indices[0] = *cast<Constant>(Src->getOperand(1)) +
|
|
*cast<Constant>(GEP.getOperand(1));
|
|
assert(Indices[0] != 0 && "Constant folding of uint's failed!?");
|
|
|
|
} else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
|
|
Src->getNumOperands() != 1) {
|
|
// Otherwise we can do the fold if the first index of the GEP is a zero
|
|
Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
|
|
Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
|
|
} else if (Src->getOperand(Src->getNumOperands()-1) ==
|
|
Constant::getNullValue(Type::LongTy)) {
|
|
// If the src gep ends with a constant array index, merge this get into
|
|
// it, even if we have a non-zero array index.
|
|
Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
|
|
Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
|
|
}
|
|
|
|
if (!Indices.empty())
|
|
return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
|
|
|
|
} else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
|
|
// GEP of global variable. If all of the indices for this GEP are
|
|
// constants, we can promote this to a constexpr instead of an instruction.
|
|
|
|
// Scan for nonconstants...
|
|
std::vector<Constant*> Indices;
|
|
User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
|
|
for (; I != E && isa<Constant>(*I); ++I)
|
|
Indices.push_back(cast<Constant>(*I));
|
|
|
|
if (I == E) { // If they are all constants...
|
|
ConstantExpr *CE =
|
|
ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
|
|
|
|
// Replace all uses of the GEP with the new constexpr...
|
|
return ReplaceInstUsesWith(GEP, CE);
|
|
}
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
|
|
// Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
|
|
if (AI.isArrayAllocation()) // Check C != 1
|
|
if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
|
|
const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
|
|
AllocationInst *New = 0;
|
|
|
|
// Create and insert the replacement instruction...
|
|
if (isa<MallocInst>(AI))
|
|
New = new MallocInst(NewTy, 0, AI.getName(), &AI);
|
|
else {
|
|
assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
|
|
New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
|
|
}
|
|
|
|
// Scan to the end of the allocation instructions, to skip over a block of
|
|
// allocas if possible...
|
|
//
|
|
BasicBlock::iterator It = New;
|
|
while (isa<AllocationInst>(*It)) ++It;
|
|
|
|
// Now that I is pointing to the first non-allocation-inst in the block,
|
|
// insert our getelementptr instruction...
|
|
//
|
|
std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
|
|
Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
|
|
|
|
// Now make everything use the getelementptr instead of the original
|
|
// allocation.
|
|
ReplaceInstUsesWith(AI, V);
|
|
return &AI;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
|
|
|
|
void InstCombiner::removeFromWorkList(Instruction *I) {
|
|
WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
|
|
WorkList.end());
|
|
}
|
|
|
|
bool InstCombiner::runOnFunction(Function &F) {
|
|
bool Changed = false;
|
|
|
|
WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
|
|
|
|
while (!WorkList.empty()) {
|
|
Instruction *I = WorkList.back(); // Get an instruction from the worklist
|
|
WorkList.pop_back();
|
|
|
|
// Check to see if we can DCE or ConstantPropagate the instruction...
|
|
// Check to see if we can DIE the instruction...
|
|
if (isInstructionTriviallyDead(I)) {
|
|
// Add operands to the worklist...
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
|
|
WorkList.push_back(Op);
|
|
|
|
++NumDeadInst;
|
|
BasicBlock::iterator BBI = I;
|
|
if (dceInstruction(BBI)) {
|
|
removeFromWorkList(I);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Instruction isn't dead, see if we can constant propagate it...
|
|
if (Constant *C = ConstantFoldInstruction(I)) {
|
|
// Add operands to the worklist...
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
|
|
WorkList.push_back(Op);
|
|
ReplaceInstUsesWith(*I, C);
|
|
|
|
++NumConstProp;
|
|
BasicBlock::iterator BBI = I;
|
|
if (dceInstruction(BBI)) {
|
|
removeFromWorkList(I);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Now that we have an instruction, try combining it to simplify it...
|
|
if (Instruction *Result = visit(*I)) {
|
|
++NumCombined;
|
|
// Should we replace the old instruction with a new one?
|
|
if (Result != I) {
|
|
// Instructions can end up on the worklist more than once. Make sure
|
|
// we do not process an instruction that has been deleted.
|
|
removeFromWorkList(I);
|
|
ReplaceInstWithInst(I, Result);
|
|
} else {
|
|
BasicBlock::iterator II = I;
|
|
|
|
// If the instruction was modified, it's possible that it is now dead.
|
|
// if so, remove it.
|
|
if (dceInstruction(II)) {
|
|
// Instructions may end up in the worklist more than once. Erase them
|
|
// all.
|
|
removeFromWorkList(I);
|
|
Result = 0;
|
|
}
|
|
}
|
|
|
|
if (Result) {
|
|
WorkList.push_back(Result);
|
|
AddUsesToWorkList(*Result);
|
|
}
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
Pass *createInstructionCombiningPass() {
|
|
return new InstCombiner();
|
|
}
|