+++ /dev/null
-//===- InductionVars.cpp - Induction Variable Cannonicalization code --------=//
-//
-// This file implements induction variable cannonicalization of loops.
-//
-// Specifically, after this executes, the following is true:
-// - There is a single induction variable for each loop (at least loops that
-// used to contain at least one induction variable)
-// * This induction variable starts at 0 and steps by 1 per iteration
-// * This induction variable is represented by the first PHI node in the
-// Header block, allowing it to be found easily.
-// - All other preexisting induction variables are adjusted to operate in
-// terms of this primary induction variable
-// - Induction variables with a step size of 0 have been eliminated.
-//
-// This code assumes the following is true to perform its full job:
-// - The CFG has been simplified to not have multiple entrances into an
-// interval header. Interval headers should only have two predecessors,
-// one from inside of the loop and one from outside of the loop.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Transforms/Scalar/InductionVars.h"
-#include "llvm/Constants.h"
-#include "llvm/iPHINode.h"
-#include "llvm/Type.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Analysis/IntervalPartition.h"
-#include "Support/STLExtras.h"
-#include <algorithm>
-#include <iostream>
-using std::cerr;
-
-// isLoopInvariant - Return true if the specified value/basic block source is
-// an interval invariant computation.
-//
-static bool isLoopInvariant(Interval *Int, Value *V) {
- assert(isa<Constant>(V) || isa<Instruction>(V) || isa<Argument>(V));
-
- if (!isa<Instruction>(V))
- return true; // Constants and arguments are always loop invariant
-
- BasicBlock *ValueBlock = cast<Instruction>(V)->getParent();
- assert(ValueBlock && "Instruction not embedded in basic block!");
-
- // For now, only consider values from outside of the interval, regardless of
- // whether the expression could be lifted out of the loop by some LICM.
- //
- // TODO: invoke LICM library if we find out it would be useful.
- //
- return !Int->contains(ValueBlock);
-}
-
-
-// isLinearInductionVariableH - Return isLIV if the expression V is a linear
-// expression defined in terms of loop invariant computations, and a single
-// instance of the PHI node PN. Return isLIC if the expression V is a loop
-// invariant computation. Return isNLIV if the expression is a negated linear
-// induction variable. Return isOther if it is neither.
-//
-// Currently allowed operators are: ADD, SUB, NEG
-// TODO: This should allow casts!
-//
-enum LIVType { isLIV, isLIC, isNLIV, isOther };
-//
-// neg - Negate the sign of a LIV expression.
-inline LIVType neg(LIVType T) {
- assert(T == isLIV || T == isNLIV && "Negate Only works on LIV expressions");
- return T == isLIV ? isNLIV : isLIV;
-}
-//
-static LIVType isLinearInductionVariableH(Interval *Int, Value *V,
- PHINode *PN) {
- if (V == PN) { return isLIV; } // PHI node references are (0+PHI)
- if (isLoopInvariant(Int, V)) return isLIC;
-
- // loop variant computations must be instructions!
- Instruction *I = cast<Instruction>(V);
- switch (I->getOpcode()) { // Handle each instruction seperately
- case Instruction::Add:
- case Instruction::Sub: {
- Value *SubV1 = cast<BinaryOperator>(I)->getOperand(0);
- Value *SubV2 = cast<BinaryOperator>(I)->getOperand(1);
- LIVType SubLIVType1 = isLinearInductionVariableH(Int, SubV1, PN);
- if (SubLIVType1 == isOther) return isOther; // Early bailout
- LIVType SubLIVType2 = isLinearInductionVariableH(Int, SubV2, PN);
-
- switch (SubLIVType2) {
- case isOther: return isOther; // Unknown subexpression type
- case isLIC: return SubLIVType1; // Constant offset, return type #1
- case isLIV:
- case isNLIV:
- // So now we know that we have a linear induction variable on the RHS of
- // the ADD or SUB instruction. SubLIVType1 cannot be isOther, so it is
- // either a Loop Invariant computation, or a LIV type.
- if (SubLIVType1 == isLIC) {
- // Loop invariant computation, we know this is a LIV then.
- return (I->getOpcode() == Instruction::Add) ?
- SubLIVType2 : neg(SubLIVType2);
- }
-
- // If the LHS is also a LIV Expression, we cannot add two LIVs together
- if (I->getOpcode() == Instruction::Add) return isOther;
-
- // We can only subtract two LIVs if they are the same type, which yields
- // a LIC, because the LIVs cancel each other out.
- return (SubLIVType1 == SubLIVType2) ? isLIC : isOther;
- }
- // NOT REACHED
- }
-
- default: // Any other instruction is not a LINEAR induction var
- return isOther;
- }
-}
-
-// isLinearInductionVariable - Return true if the specified expression is a
-// "linear induction variable", which is an expression involving a single
-// instance of the PHI node and a loop invariant value that is added or
-// subtracted to the PHI node. This is calculated by walking the SSA graph
-//
-static inline bool isLinearInductionVariable(Interval *Int, Value *V,
- PHINode *PN) {
- return isLinearInductionVariableH(Int, V, PN) == isLIV;
-}
-
-
-// isSimpleInductionVar - Return true iff the cannonical induction variable PN
-// has an initializer of the constant value 0, and has a step size of constant
-// 1.
-static inline bool isSimpleInductionVar(PHINode *PN) {
- assert(PN->getNumIncomingValues() == 2 && "Must have cannonical PHI node!");
- Value *Initializer = PN->getIncomingValue(0);
- if (!isa<Constant>(Initializer)) return false;
-
- if (Initializer->getType()->isSigned()) { // Signed constant value...
- if (((ConstantSInt*)Initializer)->getValue() != 0) return false;
- } else if (Initializer->getType()->isUnsigned()) { // Unsigned constant value
- if (((ConstantUInt*)Initializer)->getValue() != 0) return false;
- } else {
- return false; // Not signed or unsigned? Must be FP type or something
- }
-
- Value *StepExpr = PN->getIncomingValue(1);
- if (!isa<Instruction>(StepExpr) ||
- cast<Instruction>(StepExpr)->getOpcode() != Instruction::Add)
- return false;
-
- BinaryOperator *I = cast<BinaryOperator>(StepExpr);
- assert(isa<PHINode>(I->getOperand(0)) &&
- "PHI node should be first operand of ADD instruction!");
-
- // Get the right hand side of the ADD node. See if it is a constant 1.
- Value *StepSize = I->getOperand(1);
- if (!isa<Constant>(StepSize)) return false;
-
- if (StepSize->getType()->isSigned()) { // Signed constant value...
- if (((ConstantSInt*)StepSize)->getValue() != 1) return false;
- } else if (StepSize->getType()->isUnsigned()) { // Unsigned constant value
- if (((ConstantUInt*)StepSize)->getValue() != 1) return false;
- } else {
- return false; // Not signed or unsigned? Must be FP type or something
- }
-
- // At this point, we know the initializer is a constant value 0 and the step
- // size is a constant value 1. This is our simple induction variable!
- return true;
-}
-
-// InjectSimpleInductionVariable - Insert a cannonical induction variable into
-// the interval header Header. This assumes that the flow graph is in
-// simplified form (so we know that the header block has exactly 2 predecessors)
-//
-// TODO: This should inherit the largest type that is being used by the already
-// present induction variables (instead of always using uint)
-//
-static PHINode *InjectSimpleInductionVariable(Interval *Int) {
- std::string PHIName, AddName;
-
- BasicBlock *Header = Int->getHeaderNode();
- Function *M = Header->getParent();
-
- if (M->hasSymbolTable()) {
- // Only name the induction variable if the function isn't stripped.
- PHIName = "ind_var";
- AddName = "ind_var_next";
- }
-
- // Create the neccesary instructions...
- PHINode *PN = new PHINode(Type::UIntTy, PHIName);
- Constant *One = ConstantUInt::get(Type::UIntTy, 1);
- Constant *Zero = ConstantUInt::get(Type::UIntTy, 0);
- BinaryOperator *AddNode = BinaryOperator::create(Instruction::Add,
- PN, One, AddName);
-
- // Figure out which predecessors I have to play with... there should be
- // exactly two... one of which is a loop predecessor, and one of which is not.
- //
- pred_iterator PI = pred_begin(Header);
- assert(PI != pred_end(Header) && "Header node should have 2 preds!");
- BasicBlock *Pred1 = *PI; ++PI;
- assert(PI != pred_end(Header) && "Header node should have 2 preds!");
- BasicBlock *Pred2 = *PI;
- assert(++PI == pred_end(Header) && "Header node should have 2 preds!");
-
- // Make Pred1 be the loop entrance predecessor, Pred2 be the Loop predecessor
- if (Int->contains(Pred1)) std::swap(Pred1, Pred2);
-
- assert(!Int->contains(Pred1) && "Pred1 should be loop entrance!");
- assert( Int->contains(Pred2) && "Pred2 should be looping edge!");
-
- // Link the instructions into the PHI node...
- PN->addIncoming(Zero, Pred1); // The initializer is first argument
- PN->addIncoming(AddNode, Pred2); // The step size is second PHI argument
-
- // Insert the PHI node into the Header of the loop. It shall be the first
- // instruction, because the "Simple" Induction Variable must be first in the
- // block.
- //
- BasicBlock::InstListType &IL = Header->getInstList();
- IL.push_front(PN);
-
- // Insert the Add instruction as the first (non-phi) instruction in the
- // header node's basic block.
- BasicBlock::iterator I = IL.begin();
- while (isa<PHINode>(*I)) ++I;
- IL.insert(I, AddNode);
- return PN;
-}
-
-// ProcessInterval - This function is invoked once for each interval in the
-// IntervalPartition of the program. It looks for auxilliary induction
-// variables in loops. If it finds one, it:
-// * Cannonicalizes the induction variable. This consists of:
-// A. Making the first element of the PHI node be the loop invariant
-// computation, and the second element be the linear induction portion.
-// B. Changing the first element of the linear induction portion of the PHI
-// node to be of the form ADD(PHI, <loop invariant expr>).
-// * Add the induction variable PHI to a list of induction variables found.
-//
-// After this, a list of cannonical induction variables is known. This list
-// is searched to see if there is an induction variable that counts from
-// constant 0 with a step size of constant 1. If there is not one, one is
-// injected into the loop. Thus a "simple" induction variable is always known
-//
-// One a simple induction variable is known, all other induction variables are
-// modified to refer to the "simple" induction variable.
-//
-static bool ProcessInterval(Interval *Int) {
- if (!Int->isLoop()) return false; // Not a loop? Ignore it!
-
- std::vector<PHINode *> InductionVars;
-
- BasicBlock *Header = Int->getHeaderNode();
- // Loop over all of the PHI nodes in the interval header...
- for (BasicBlock::iterator I = Header->begin(), E = Header->end();
- I != E && isa<PHINode>(*I); ++I) {
- PHINode *PN = cast<PHINode>(*I);
- if (PN->getNumIncomingValues() != 2) { // These should be eliminated by now.
- cerr << "Found interval header with more than 2 predecessors! Ignoring\n";
- return false; // Todo, make an assertion.
- }
-
- // For this to be an induction variable, one of the arguments must be a
- // loop invariant expression, and the other must be an expression involving
- // the PHI node, along with possible additions and subtractions of loop
- // invariant values.
- //
- BasicBlock *BB1 = PN->getIncomingBlock(0);
- Value *V1 = PN->getIncomingValue(0);
- BasicBlock *BB2 = PN->getIncomingBlock(1);
- Value *V2 = PN->getIncomingValue(1);
-
- // Figure out which computation is loop invariant...
- if (!isLoopInvariant(Int, V1)) {
- // V1 is *not* loop invariant. Check to see if V2 is:
- if (isLoopInvariant(Int, V2)) {
- // They *are* loop invariant. Exchange BB1/BB2 and V1/V2 so that
- // V1 is always the loop invariant computation.
- std::swap(V1, V2); std::swap(BB1, BB2);
- } else {
- // Neither value is loop invariant. Must not be an induction variable.
- // This case can happen if there is an unreachable loop in the CFG that
- // has two tail loops in it that was not split by the cleanup phase
- // before.
- continue;
- }
- }
-
- // At this point, we know that BB1/V1 are loop invariant. We don't know
- // anything about BB2/V2. Check now to see if V2 is a linear induction
- // variable.
- //
- cerr << "Found loop invariant computation: " << V1 << "\n";
-
- if (!isLinearInductionVariable(Int, V2, PN))
- continue; // No, it is not a linear ind var, ignore the PHI node.
- cerr << "Found linear induction variable: " << V2;
-
- // TODO: Cannonicalize V2
-
- // Add this PHI node to the list of induction variables found...
- InductionVars.push_back(PN);
- }
-
- // No induction variables found?
- if (InductionVars.empty()) return false;
-
- // Search to see if there is already a "simple" induction variable.
- std::vector<PHINode*>::iterator It =
- find_if(InductionVars.begin(), InductionVars.end(), isSimpleInductionVar);
-
- PHINode *PrimaryIndVar;
-
- // A simple induction variable was not found, inject one now...
- if (It == InductionVars.end()) {
- PrimaryIndVar = InjectSimpleInductionVariable(Int);
- } else {
- // Move the PHI node for this induction variable to the start of the PHI
- // list in HeaderNode... we do not need to do this for the inserted case
- // because the inserted node will always be placed at the beginning of
- // HeaderNode.
- //
- PrimaryIndVar = *It;
- BasicBlock::iterator i =
- find(Header->begin(), Header->end(), PrimaryIndVar);
- assert(i != Header->end() &&
- "How could Primary IndVar not be in the header!?!!?");
-
- if (i != Header->begin())
- std::iter_swap(i, Header->begin());
- }
-
- // Now we know that there is a simple induction variable PrimaryIndVar.
- // Simplify all of the other induction variables to use this induction
- // variable as their counter, and destroy the PHI nodes that correspond to
- // the old indvars.
- //
- // TODO
-
-
- cerr << "Found Interval Header with indvars (primary indvar should be first "
- << "phi): \n" << Header << "\nPrimaryIndVar: " << PrimaryIndVar;
-
- return false; // TODO: true;
-}
-
-
-// ProcessIntervalPartition - This function loops over the interval partition
-// processing each interval with ProcessInterval
-//
-static bool ProcessIntervalPartition(IntervalPartition &IP) {
- // This currently just prints out information about the interval structure
- // of the function...
-#if 0
- static unsigned N = 0;
- cerr << "\n***********Interval Partition #" << (++N) << "************\n\n";
- copy(IP.begin(), IP.end(), ostream_iterator<Interval*>(cerr, "\n"));
-
- cerr << "\n*********** PERFORMING WORK ************\n\n";
-#endif
- // Loop over all of the intervals in the partition and look for induction
- // variables in intervals that represent loops.
- //
- return reduce_apply(IP.begin(), IP.end(), bitwise_or<bool>(), false,
- std::ptr_fun(ProcessInterval));
-}
-
-// DoInductionVariableCannonicalize - Simplify induction variables in loops.
-// This function loops over an interval partition of a program, reducing it
-// until the graph is gone.
-//
-bool InductionVariableCannonicalize::doIt(Function *M, IntervalPartition &IP) {
-
- bool Changed = false;
-
-#if 0
- while (!IP->isDegeneratePartition()) {
- Changed |= ProcessIntervalPartition(*IP);
-
- // Calculate the reduced version of this graph until we get to an
- // irreducible graph or a degenerate graph...
- //
- IntervalPartition *NewIP = new IntervalPartition(*IP, false);
- if (NewIP->size() == IP->size()) {
- cerr << "IRREDUCIBLE GRAPH FOUND!!!\n";
- return Changed;
- }
- delete IP;
- IP = NewIP;
- }
-
- delete IP;
-#endif
- return Changed;
-}
-
-
-bool InductionVariableCannonicalize::runOnFunction(Function *F) {
- return doIt(F, getAnalysis<IntervalPartition>());
-}
-
-// getAnalysisUsage - This function works on the call graph of a module.
-// It is capable of updating the call graph to reflect the new state of the
-// module.
-//
-void InductionVariableCannonicalize::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired(IntervalPartition::ID);
-}
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