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Remove unused files: This is the old induction varaible cannonicalization

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pass built on top of interval analysis


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2411 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-04-29 20:18:00 +00:00
parent 8ac58a83eb
commit 94cf3b1c67
2 changed files with 0 additions and 435 deletions
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27
include/llvm/Transforms/Scalar/InductionVars.h
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//===-- InductionVars.h - Induction Variable Recognition ---------*- C++ -*--=//
//
// This family of functions is useful for Induction variable recognition,
// removal and optimizations.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_OPT_INDUCTION_VARS_H
#define LLVM_OPT_INDUCTION_VARS_H
#include "llvm/Pass.h"
class IntervalPartition;
struct InductionVariableCannonicalize : public FunctionPass {
const char *getPassName() const { return "**OLD IndVars ***"; }
// doInductionVariableCannonicalize - Simplify induction variables in loops
//
static bool doIt(Function *F, IntervalPartition &IP);
virtual bool runOnFunction(Function *F);
// getAnalysisUsage - Declare that we need IntervalPartitions
void getAnalysisUsage(AnalysisUsage &AU) const;
};
#endif

408
lib/Transforms/Scalar/InductionVars.cpp
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//===- 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);
}