mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-11-25 12:12:47 +01:00
240 lines
8.4 KiB
C++
240 lines
8.4 KiB
C++
//===- ConstantProp.cpp - Code to perform Constant Propogation ------------===//
|
|
//
|
|
// This file implements constant propogation and merging:
|
|
//
|
|
// Specifically, this:
|
|
// * Folds multiple identical constants in the constant pool together
|
|
// Note that if one is named and the other is not, that the result gets the
|
|
// original name.
|
|
// * Converts instructions like "add int %1, %2" into a direct def of %3 in
|
|
// the constant pool
|
|
// * Converts conditional branches on a constant boolean value into direct
|
|
// branches.
|
|
// * Converts phi nodes with one incoming def to the incoming def directly
|
|
// . Converts switch statements with one entry into a test & conditional
|
|
// branch
|
|
// . Converts switches on constant values into an unconditional branch.
|
|
//
|
|
// Notice that:
|
|
// * This pass has a habit of making definitions be dead. It is a good idea
|
|
// to to run a DCE pass sometime after running this pass.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Module.h"
|
|
#include "llvm/Method.h"
|
|
#include "llvm/BasicBlock.h"
|
|
#include "llvm/iTerminators.h"
|
|
#include "llvm/iOther.h"
|
|
#include "llvm/ConstPoolVals.h"
|
|
#include "llvm/ConstantPool.h"
|
|
#include "llvm/Opt/AllOpts.h"
|
|
#include "llvm/Opt/ConstantHandling.h"
|
|
|
|
// Merge identical constant values in the constant pool.
|
|
//
|
|
// TODO: We can do better than this simplistic N^2 algorithm...
|
|
//
|
|
static bool MergeConstantPoolReferences(ConstantPool &CP) {
|
|
bool Modified = false;
|
|
for (ConstantPool::plane_iterator PI = CP.begin(); PI != CP.end(); ++PI) {
|
|
for (ConstantPool::PlaneType::iterator I = (*PI)->begin();
|
|
I != (*PI)->end(); I++) {
|
|
ConstPoolVal *C = *I;
|
|
|
|
ConstantPool::PlaneType::iterator J = I;
|
|
for (++J; J != (*PI)->end(); J++) {
|
|
if (C->equals(*J)) {
|
|
Modified = true;
|
|
// Okay we know that *I == *J. So now we need to make all uses of *I
|
|
// point to *J.
|
|
//
|
|
C->replaceAllUsesWith(*J);
|
|
|
|
(*PI)->remove(I); // Remove C from constant pool...
|
|
|
|
if (C->hasName() && !(*J)->hasName()) // The merged constant inherits
|
|
(*J)->setName(C->getName()); // the old name...
|
|
|
|
delete C; // Delete the constant itself.
|
|
break; // Break out of inner for loop
|
|
}
|
|
}
|
|
}
|
|
}
|
|
return Modified;
|
|
}
|
|
|
|
inline static bool
|
|
ConstantFoldUnaryInst(Method *M, Method::inst_iterator &DI,
|
|
UnaryOperator *Op, ConstPoolVal *D) {
|
|
ConstPoolVal *ReplaceWith = 0;
|
|
|
|
switch (Op->getInstType()) {
|
|
case Instruction::Not: ReplaceWith = !*D; break;
|
|
case Instruction::Neg: ReplaceWith = -*D; break;
|
|
}
|
|
|
|
if (!ReplaceWith) return false; // Nothing new to change...
|
|
|
|
|
|
// Add the new value to the constant pool...
|
|
M->getConstantPool().insert(ReplaceWith);
|
|
|
|
// Replaces all of the uses of a variable with uses of the constant.
|
|
Op->replaceAllUsesWith(ReplaceWith);
|
|
|
|
// Remove the operator from the list of definitions...
|
|
Op->getParent()->getInstList().remove(DI.getInstructionIterator());
|
|
|
|
// The new constant inherits the old name of the operator...
|
|
if (Op->hasName()) ReplaceWith->setName(Op->getName());
|
|
|
|
// Delete the operator now...
|
|
delete Op;
|
|
return true;
|
|
}
|
|
|
|
inline static bool
|
|
ConstantFoldBinaryInst(Method *M, Method::inst_iterator &DI,
|
|
BinaryOperator *Op,
|
|
ConstPoolVal *D1, ConstPoolVal *D2) {
|
|
ConstPoolVal *ReplaceWith = 0;
|
|
|
|
switch (Op->getInstType()) {
|
|
case Instruction::Add: ReplaceWith = *D1 + *D2; break;
|
|
case Instruction::Sub: ReplaceWith = *D1 - *D2; break;
|
|
|
|
case Instruction::SetEQ: ReplaceWith = *D1 == *D2; break;
|
|
case Instruction::SetNE: ReplaceWith = *D1 != *D2; break;
|
|
case Instruction::SetLE: ReplaceWith = *D1 <= *D2; break;
|
|
case Instruction::SetGE: ReplaceWith = *D1 >= *D2; break;
|
|
case Instruction::SetLT: ReplaceWith = *D1 < *D2; break;
|
|
case Instruction::SetGT: ReplaceWith = *D1 > *D2; break;
|
|
}
|
|
|
|
if (!ReplaceWith) return false; // Nothing new to change...
|
|
|
|
// Add the new value to the constant pool...
|
|
M->getConstantPool().insert(ReplaceWith);
|
|
|
|
// Replaces all of the uses of a variable with uses of the constant.
|
|
Op->replaceAllUsesWith(ReplaceWith);
|
|
|
|
// Remove the operator from the list of definitions...
|
|
Op->getParent()->getInstList().remove(DI.getInstructionIterator());
|
|
|
|
// The new constant inherits the old name of the operator...
|
|
if (Op->hasName()) ReplaceWith->setName(Op->getName());
|
|
|
|
// Delete the operator now...
|
|
delete Op;
|
|
return true;
|
|
}
|
|
|
|
inline static bool ConstantFoldTerminator(TerminatorInst *T) {
|
|
// Branch - See if we are conditional jumping on constant
|
|
if (T->getInstType() == Instruction::Br) {
|
|
BranchInst *BI = (BranchInst*)T;
|
|
if (!BI->isUnconditional() && // Are we branching on constant?
|
|
BI->getOperand(2)->getValueType() == Value::ConstantVal) {
|
|
// YES. Change to unconditional branch...
|
|
ConstPoolBool *Cond = (ConstPoolBool*)BI->getOperand(2);
|
|
Value *Destination = BI->getOperand(Cond->getValue() ? 0 : 1);
|
|
|
|
BI->setOperand(0, Destination); // Set the unconditional destination
|
|
BI->setOperand(1, 0); // Clear the conditional destination
|
|
BI->setOperand(2, 0); // Clear the condition...
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// ConstantFoldInstruction - If an instruction references constants, try to fold
|
|
// them together...
|
|
//
|
|
inline static bool
|
|
ConstantFoldInstruction(Method *M, Method::inst_iterator &II) {
|
|
Instruction *Inst = *II;
|
|
if (Inst->isBinaryOp()) {
|
|
Value *D1, *D2;
|
|
if (((D1 = Inst->getOperand(0))->getValueType() == Value::ConstantVal) &
|
|
((D2 = Inst->getOperand(1))->getValueType() == Value::ConstantVal))
|
|
return ConstantFoldBinaryInst(M, II, (BinaryOperator*)Inst,
|
|
(ConstPoolVal*)D1, (ConstPoolVal*)D2);
|
|
|
|
} else if (Inst->isUnaryOp()) {
|
|
Value *D;
|
|
if ((D = Inst->getOperand(0))->getValueType() == Value::ConstantVal)
|
|
return ConstantFoldUnaryInst(M, II, (UnaryOperator*)Inst,
|
|
(ConstPoolVal*)D);
|
|
} else if (Inst->isTerminator()) {
|
|
return ConstantFoldTerminator((TerminatorInst*)Inst);
|
|
|
|
} else if (Inst->getInstType() == Instruction::PHINode) {
|
|
PHINode *PN = (PHINode*)Inst; // If it's a PHI node and only has one operand
|
|
// Then replace it directly with that operand.
|
|
assert(PN->getOperand(0) && "PHI Node must have at least one operand!");
|
|
if (PN->getOperand(1) == 0) { // If the PHI Node has exactly 1 operand
|
|
Value *V = PN->getOperand(0);
|
|
PN->replaceAllUsesWith(V); // Replace all uses of this PHI
|
|
// Unlink from basic block
|
|
PN->getParent()->getInstList().remove(II.getInstructionIterator());
|
|
if (PN->hasName()) V->setName(PN->getName()); // Inherit PHINode name
|
|
delete PN; // Finally, delete the node...
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// DoConstPropPass - Propogate constants and do constant folding on instructions
|
|
// this returns true if something was changed, false if nothing was changed.
|
|
//
|
|
static bool DoConstPropPass(Method *M) {
|
|
bool SomethingChanged = false;
|
|
|
|
#if 1
|
|
Method::inst_iterator It = M->inst_begin();
|
|
while (It != M->inst_end())
|
|
if (ConstantFoldInstruction(M, It)) {
|
|
SomethingChanged = true; // If returned true, iter is already incremented
|
|
|
|
// Incrementing the iterator in an unchecked manner could mess up the
|
|
// internals of 'It'. To make sure everything is happy, tell it we might
|
|
// have broken it.
|
|
It.resyncInstructionIterator();
|
|
} else {
|
|
++It;
|
|
}
|
|
#else
|
|
Method::BasicBlocksType::iterator BBIt = M->getBasicBlocks().begin();
|
|
for (; BBIt != M->getBasicBlocks().end(); BBIt++) {
|
|
BasicBlock *BB = *BBIt;
|
|
|
|
BasicBlock::InstListType::iterator DI = BB->getInstList().begin();
|
|
for (; DI != BB->getInstList().end(); DI++)
|
|
SomethingChanged |= ConstantFoldInstruction(M, DI);
|
|
}
|
|
#endif
|
|
return SomethingChanged;
|
|
}
|
|
|
|
|
|
// returns true on failure, false on success...
|
|
//
|
|
bool DoConstantPropogation(Method *M) {
|
|
bool Modified = false;
|
|
|
|
// Fold constants until we make no progress...
|
|
while (DoConstPropPass(M)) Modified = true;
|
|
|
|
// Merge identical constants last: this is important because we may have just
|
|
// introduced constants that already exist!
|
|
//
|
|
Modified |= MergeConstantPoolReferences(M->getConstantPool());
|
|
|
|
return Modified;
|
|
}
|