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https://github.com/c64scene-ar/llvm-6502.git
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change references from MethodARgument to FunctionArgument git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1991 91177308-0d34-0410-b5e6-96231b3b80d8
522 lines
19 KiB
C++
522 lines
19 KiB
C++
//===- SCCP.cpp - Sparse Conditional Constant Propogation -----------------===//
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//
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// This file implements sparse conditional constant propogation and merging:
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//
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// Specifically, this:
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// * Assumes values are constant unless proven otherwise
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// * Assumes BasicBlocks are dead unless proven otherwise
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// * Proves values to be constant, and replaces them with constants
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// . Proves conditional branches constant, and unconditionalizes them
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// * Folds multiple identical constants in the constant pool together
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//
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// Notice that:
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// * This pass has a habit of making definitions be dead. It is a good idea
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// to to run a DCE pass sometime after running this pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/ConstantProp.h"
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#include "llvm/Transforms/Scalar/ConstantHandling.h"
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#include "llvm/Function.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/ConstantVals.h"
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#include "llvm/iPHINode.h"
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#include "llvm/iMemory.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iOther.h"
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#include "llvm/Pass.h"
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#include "llvm/Assembly/Writer.h"
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#include "Support/STLExtras.h"
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#include <algorithm>
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#include <map>
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#include <set>
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#include <iostream>
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using std::cerr;
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// InstVal class - This class represents the different lattice values that an
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// instruction may occupy. It is a simple class with value semantics. The
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// potential constant value that is pointed to is owned by the constant pool
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// for the method being optimized.
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//
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class InstVal {
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enum {
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undefined, // This instruction has no known value
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constant, // This instruction has a constant value
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// Range, // This instruction is known to fall within a range
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overdefined // This instruction has an unknown value
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} LatticeValue; // The current lattice position
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Constant *ConstantVal; // If Constant value, the current value
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public:
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inline InstVal() : LatticeValue(undefined), ConstantVal(0) {}
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// markOverdefined - Return true if this is a new status to be in...
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inline bool markOverdefined() {
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if (LatticeValue != overdefined) {
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LatticeValue = overdefined;
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return true;
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}
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return false;
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}
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// markConstant - Return true if this is a new status for us...
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inline bool markConstant(Constant *V) {
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if (LatticeValue != constant) {
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LatticeValue = constant;
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ConstantVal = V;
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return true;
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} else {
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assert(ConstantVal == V && "Marking constant with different value");
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}
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return false;
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}
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inline bool isUndefined() const { return LatticeValue == undefined; }
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inline bool isConstant() const { return LatticeValue == constant; }
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inline bool isOverdefined() const { return LatticeValue == overdefined; }
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inline Constant *getConstant() const { return ConstantVal; }
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};
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//===----------------------------------------------------------------------===//
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// SCCP Class
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//
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// This class does all of the work of Sparse Conditional Constant Propogation.
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// It's public interface consists of a constructor and a doSCCP() method.
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//
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class SCCP {
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Function *M; // The function that we are working on
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std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
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std::map<Value*, InstVal> ValueState; // The state each value is in...
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std::vector<Instruction*> InstWorkList;// The instruction work list
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std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
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//===--------------------------------------------------------------------===//
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// The public interface for this class
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//
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public:
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// SCCP Ctor - Save the method to operate on...
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inline SCCP(Function *f) : M(f) {}
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// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
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// return true if the method was modified.
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bool doSCCP();
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//===--------------------------------------------------------------------===//
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// The implementation of this class
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//
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private:
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// markValueOverdefined - Make a value be marked as "constant". If the value
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// is not already a constant, add it to the instruction work list so that
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// the users of the instruction are updated later.
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//
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inline bool markConstant(Instruction *I, Constant *V) {
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//cerr << "markConstant: " << V << " = " << I;
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if (ValueState[I].markConstant(V)) {
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InstWorkList.push_back(I);
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return true;
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}
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return false;
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}
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// markValueOverdefined - Make a value be marked as "overdefined". If the
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// value is not already overdefined, add it to the instruction work list so
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// that the users of the instruction are updated later.
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//
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inline bool markOverdefined(Value *V) {
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if (ValueState[V].markOverdefined()) {
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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//cerr << "markOverdefined: " << V;
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InstWorkList.push_back(I); // Only instructions go on the work list
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}
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return true;
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}
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return false;
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}
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// getValueState - Return the InstVal object that corresponds to the value.
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// This function is neccesary because not all values should start out in the
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// underdefined state... FunctionArgument's should be overdefined, and
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// constants should be marked as constants. If a value is not known to be an
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// Instruction object, then use this accessor to get its value from the map.
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//
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inline InstVal &getValueState(Value *V) {
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std::map<Value*, InstVal>::iterator I = ValueState.find(V);
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if (I != ValueState.end()) return I->second; // Common case, in the map
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if (Constant *CPV = dyn_cast<Constant>(V)) { // Constants are constant
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ValueState[CPV].markConstant(CPV);
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} else if (isa<FunctionArgument>(V)) { // FuncArgs are overdefined
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ValueState[V].markOverdefined();
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}
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// All others are underdefined by default...
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return ValueState[V];
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}
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// markExecutable - Mark a basic block as executable, adding it to the BB
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// work list if it is not already executable...
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//
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void markExecutable(BasicBlock *BB) {
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if (BBExecutable.count(BB)) return;
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//cerr << "Marking BB Executable: " << BB;
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BBExecutable.insert(BB); // Basic block is executable!
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BBWorkList.push_back(BB); // Add the block to the work list!
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}
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// UpdateInstruction - Something changed in this instruction... Either an
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// operand made a transition, or the instruction is newly executable. Change
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// the value type of I to reflect these changes if appropriate.
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//
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void UpdateInstruction(Instruction *I);
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// OperandChangedState - This method is invoked on all of the users of an
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// instruction that was just changed state somehow.... Based on this
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// information, we need to update the specified user of this instruction.
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//
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void OperandChangedState(User *U);
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};
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//===----------------------------------------------------------------------===//
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// SCCP Class Implementation
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// doSCCP() - Run the Sparse Conditional Constant Propogation algorithm, and
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// return true if the method was modified.
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//
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bool SCCP::doSCCP() {
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// Mark the first block of the method as being executable...
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markExecutable(M->front());
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// Process the work lists until their are empty!
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while (!BBWorkList.empty() || !InstWorkList.empty()) {
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// Process the instruction work list...
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while (!InstWorkList.empty()) {
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Instruction *I = InstWorkList.back();
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InstWorkList.pop_back();
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//cerr << "\nPopped off I-WL: " << I;
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// "I" got into the work list because it either made the transition from
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// bottom to constant, or to Overdefined.
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//
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// Update all of the users of this instruction's value...
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//
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for_each(I->use_begin(), I->use_end(),
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bind_obj(this, &SCCP::OperandChangedState));
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}
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// Process the basic block work list...
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while (!BBWorkList.empty()) {
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BasicBlock *BB = BBWorkList.back();
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BBWorkList.pop_back();
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//cerr << "\nPopped off BBWL: " << BB;
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// If this block only has a single successor, mark it as executable as
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// well... if not, terminate the do loop.
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//
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if (BB->getTerminator()->getNumSuccessors() == 1)
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markExecutable(BB->getTerminator()->getSuccessor(0));
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// Loop over all of the instructions and notify them that they are newly
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// executable...
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for_each(BB->begin(), BB->end(),
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bind_obj(this, &SCCP::UpdateInstruction));
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}
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}
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#if 0
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for (Function::iterator BBI = M->begin(), BBEnd = M->end();
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BBI != BBEnd; ++BBI)
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if (!BBExecutable.count(*BBI))
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cerr << "BasicBlock Dead:" << *BBI;
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#endif
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// Iterate over all of the instructions in a method, replacing them with
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// constants if we have found them to be of constant values.
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//
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bool MadeChanges = false;
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for (Function::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI) {
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BasicBlock *BB = *MI;
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for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
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Instruction *Inst = *BI;
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InstVal &IV = ValueState[Inst];
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if (IV.isConstant()) {
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Constant *Const = IV.getConstant();
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// cerr << "Constant: " << Inst << " is: " << Const;
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// Replaces all of the uses of a variable with uses of the constant.
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Inst->replaceAllUsesWith(Const);
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// Remove the operator from the list of definitions...
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BB->getInstList().remove(BI);
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// The new constant inherits the old name of the operator...
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if (Inst->hasName() && !Const->hasName())
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Const->setName(Inst->getName(), M->getSymbolTableSure());
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// Delete the operator now...
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delete Inst;
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// Hey, we just changed something!
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MadeChanges = true;
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} else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Inst)) {
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MadeChanges |= ConstantFoldTerminator(BB, BI, TI);
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}
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++BI;
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}
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}
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// Merge identical constants last: this is important because we may have just
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// introduced constants that already exist, and we don't want to pollute later
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// stages with extraneous constants.
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//
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return MadeChanges;
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}
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// UpdateInstruction - Something changed in this instruction... Either an
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// operand made a transition, or the instruction is newly executable. Change
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// the value type of I to reflect these changes if appropriate. This method
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// makes sure to do the following actions:
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//
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// 1. If a phi node merges two constants in, and has conflicting value coming
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// from different branches, or if the PHI node merges in an overdefined
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// value, then the PHI node becomes overdefined.
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// 2. If a phi node merges only constants in, and they all agree on value, the
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// PHI node becomes a constant value equal to that.
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// 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
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// 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
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// 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
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// 6. If a conditional branch has a value that is constant, make the selected
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// destination executable
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// 7. If a conditional branch has a value that is overdefined, make all
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// successors executable.
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//
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void SCCP::UpdateInstruction(Instruction *I) {
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InstVal &IValue = ValueState[I];
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if (IValue.isOverdefined())
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return; // If already overdefined, we aren't going to effect anything
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switch (I->getOpcode()) {
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//===-----------------------------------------------------------------===//
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// Handle PHI nodes...
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//
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case Instruction::PHINode: {
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PHINode *PN = cast<PHINode>(I);
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unsigned NumValues = PN->getNumIncomingValues(), i;
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InstVal *OperandIV = 0;
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// Look at all of the executable operands of the PHI node. If any of them
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// are overdefined, the PHI becomes overdefined as well. If they are all
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// constant, and they agree with each other, the PHI becomes the identical
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// constant. If they are constant and don't agree, the PHI is overdefined.
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// If there are no executable operands, the PHI remains undefined.
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//
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for (i = 0; i < NumValues; ++i) {
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if (BBExecutable.count(PN->getIncomingBlock(i))) {
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InstVal &IV = getValueState(PN->getIncomingValue(i));
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if (IV.isUndefined()) continue; // Doesn't influence PHI node.
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if (IV.isOverdefined()) { // PHI node becomes overdefined!
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markOverdefined(PN);
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return;
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}
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if (OperandIV == 0) { // Grab the first value...
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OperandIV = &IV;
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} else { // Another value is being merged in!
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// There is already a reachable operand. If we conflict with it,
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// then the PHI node becomes overdefined. If we agree with it, we
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// can continue on.
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// Check to see if there are two different constants merging...
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if (IV.getConstant() != OperandIV->getConstant()) {
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// Yes there is. This means the PHI node is not constant.
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// You must be overdefined poor PHI.
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//
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markOverdefined(I); // The PHI node now becomes overdefined
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return; // I'm done analyzing you
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}
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}
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}
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}
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// If we exited the loop, this means that the PHI node only has constant
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// arguments that agree with each other(and OperandIV is a pointer to one
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// of their InstVal's) or OperandIV is null because there are no defined
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// incoming arguments. If this is the case, the PHI remains undefined.
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//
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if (OperandIV) {
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assert(OperandIV->isConstant() && "Should only be here for constants!");
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markConstant(I, OperandIV->getConstant()); // Aquire operand value
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}
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return;
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}
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//===-----------------------------------------------------------------===//
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// Handle instructions that unconditionally provide overdefined values...
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//
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case Instruction::Malloc:
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case Instruction::Free:
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case Instruction::Alloca:
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case Instruction::Load:
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case Instruction::Store:
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// TODO: getfield
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case Instruction::Call:
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case Instruction::Invoke:
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markOverdefined(I); // Memory and call's are all overdefined
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return;
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//===-----------------------------------------------------------------===//
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// Handle Terminator instructions...
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//
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case Instruction::Ret: return; // Function return doesn't affect anything
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case Instruction::Br: { // Handle conditional branches...
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BranchInst *BI = cast<BranchInst>(I);
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if (BI->isUnconditional())
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return; // Unconditional branches are already handled!
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InstVal &BCValue = getValueState(BI->getCondition());
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if (BCValue.isOverdefined()) {
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// Overdefined condition variables mean the branch could go either way.
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markExecutable(BI->getSuccessor(0));
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markExecutable(BI->getSuccessor(1));
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} else if (BCValue.isConstant()) {
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// Constant condition variables mean the branch can only go a single way.
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ConstantBool *CPB = cast<ConstantBool>(BCValue.getConstant());
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if (CPB->getValue()) // If the branch condition is TRUE...
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markExecutable(BI->getSuccessor(0));
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else // Else if the br cond is FALSE...
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markExecutable(BI->getSuccessor(1));
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}
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return;
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}
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case Instruction::Switch: {
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SwitchInst *SI = cast<SwitchInst>(I);
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InstVal &SCValue = getValueState(SI->getCondition());
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if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
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for(unsigned i = 0; BasicBlock *Succ = SI->getSuccessor(i); ++i)
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markExecutable(Succ);
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} else if (SCValue.isConstant()) {
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Constant *CPV = SCValue.getConstant();
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// Make sure to skip the "default value" which isn't a value
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for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
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if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
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markExecutable(SI->getSuccessor(i));
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return;
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}
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}
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// Constant value not equal to any of the branches... must execute
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// default branch then...
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markExecutable(SI->getDefaultDest());
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}
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return;
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}
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default: break; // Handle math operators as groups.
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} // end switch(I->getOpcode())
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//===-------------------------------------------------------------------===//
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// Handle Unary instructions...
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// Also treated as unary here, are cast instructions and getelementptr
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// instructions on struct* operands.
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//
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if (isa<UnaryOperator>(I) || isa<CastInst>(I) ||
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(isa<GetElementPtrInst>(I) &&
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cast<GetElementPtrInst>(I)->isStructSelector())) {
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Value *V = I->getOperand(0);
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InstVal &VState = getValueState(V);
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if (VState.isOverdefined()) { // Inherit overdefinedness of operand
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markOverdefined(I);
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} else if (VState.isConstant()) { // Propogate constant value
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Constant *Result = isa<CastInst>(I)
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? ConstantFoldCastInstruction(VState.getConstant(), I->getType())
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: ConstantFoldUnaryInstruction(I->getOpcode(), VState.getConstant());
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if (Result) {
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// This instruction constant folds!
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markConstant(I, Result);
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} else {
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markOverdefined(I); // Don't know how to fold this instruction. :(
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}
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}
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return;
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}
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//===-----------------------------------------------------------------===//
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// Handle Binary instructions...
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//
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if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
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Value *V1 = I->getOperand(0);
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Value *V2 = I->getOperand(1);
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InstVal &V1State = getValueState(V1);
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InstVal &V2State = getValueState(V2);
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if (V1State.isOverdefined() || V2State.isOverdefined()) {
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markOverdefined(I);
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} else if (V1State.isConstant() && V2State.isConstant()) {
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Constant *Result =
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ConstantFoldBinaryInstruction(I->getOpcode(),
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V1State.getConstant(),
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V2State.getConstant());
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if (Result) {
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// This instruction constant folds!
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markConstant(I, Result);
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} else {
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markOverdefined(I); // Don't know how to fold this instruction. :(
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}
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}
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return;
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}
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// Shouldn't get here... either the switch statement or one of the group
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// handlers should have kicked in...
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//
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cerr << "SCCP: Don't know how to handle: " << I;
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markOverdefined(I); // Just in case
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}
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// OperandChangedState - This method is invoked on all of the users of an
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// instruction that was just changed state somehow.... Based on this
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// information, we need to update the specified user of this instruction.
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//
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void SCCP::OperandChangedState(User *U) {
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// Only instructions use other variable values!
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Instruction *I = cast<Instruction>(U);
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if (!BBExecutable.count(I->getParent())) return; // Inst not executable yet!
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UpdateInstruction(I);
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}
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namespace {
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// SCCPPass - Use Sparse Conditional Constant Propogation
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// to prove whether a value is constant and whether blocks are used.
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//
|
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struct SCCPPass : public MethodPass {
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inline bool runOnMethod(Function *F) {
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SCCP S(F);
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return S.doSCCP();
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}
|
|
};
|
|
}
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|
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Pass *createSCCPPass() {
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return new SCCPPass();
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|
}
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