mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-20 11:29:24 +00:00
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1588 91177308-0d34-0410-b5e6-96231b3b80d8
304 lines
11 KiB
C++
304 lines
11 KiB
C++
//===- ADCE.cpp - Code to perform agressive dead code elimination ---------===//
|
|
//
|
|
// This file implements "agressive" dead code elimination. ADCE is DCe where
|
|
// values are assumed to be dead until proven otherwise. This is similar to
|
|
// SCCP, except applied to the liveness of values.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Transforms/Scalar/DCE.h"
|
|
#include "llvm/Instruction.h"
|
|
#include "llvm/Type.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Analysis/Writer.h"
|
|
#include "llvm/iTerminators.h"
|
|
#include "llvm/iPHINode.h"
|
|
#include "Support/STLExtras.h"
|
|
#include "Support/DepthFirstIterator.h"
|
|
#include <algorithm>
|
|
#include <iostream>
|
|
using std::cerr;
|
|
|
|
#define DEBUG_ADCE 1
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// ADCE Class
|
|
//
|
|
// This class does all of the work of Agressive Dead Code Elimination.
|
|
// It's public interface consists of a constructor and a doADCE() method.
|
|
//
|
|
class ADCE {
|
|
Method *M; // The method that we are working on...
|
|
std::vector<Instruction*> WorkList; // Instructions that just became live
|
|
std::set<Instruction*> LiveSet; // The set of live instructions
|
|
bool MadeChanges;
|
|
|
|
//===--------------------------------------------------------------------===//
|
|
// The public interface for this class
|
|
//
|
|
public:
|
|
// ADCE Ctor - Save the method to operate on...
|
|
inline ADCE(Method *m) : M(m), MadeChanges(false) {}
|
|
|
|
// doADCE() - Run the Agressive Dead Code Elimination algorithm, returning
|
|
// true if the method was modified.
|
|
bool doADCE();
|
|
|
|
//===--------------------------------------------------------------------===//
|
|
// The implementation of this class
|
|
//
|
|
private:
|
|
inline void markInstructionLive(Instruction *I) {
|
|
if (LiveSet.count(I)) return;
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Insn Live: " << I;
|
|
#endif
|
|
LiveSet.insert(I);
|
|
WorkList.push_back(I);
|
|
}
|
|
|
|
inline void markTerminatorLive(const BasicBlock *BB) {
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Terminat Live: " << BB->getTerminator();
|
|
#endif
|
|
markInstructionLive((Instruction*)BB->getTerminator());
|
|
}
|
|
|
|
// fixupCFG - Walk the CFG in depth first order, eliminating references to
|
|
// dead blocks.
|
|
//
|
|
BasicBlock *fixupCFG(BasicBlock *Head, std::set<BasicBlock*> &VisitedBlocks,
|
|
const std::set<BasicBlock*> &AliveBlocks);
|
|
};
|
|
|
|
|
|
|
|
// doADCE() - Run the Agressive Dead Code Elimination algorithm, returning
|
|
// true if the method was modified.
|
|
//
|
|
bool ADCE::doADCE() {
|
|
// Compute the control dependence graph... Note that this has a side effect
|
|
// on the CFG: a new return bb is added and all returns are merged here.
|
|
//
|
|
cfg::DominanceFrontier CDG(cfg::DominatorSet(M, true));
|
|
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Method: " << M;
|
|
#endif
|
|
|
|
// Iterate over all of the instructions in the method, eliminating trivially
|
|
// dead instructions, and marking instructions live that are known to be
|
|
// needed. Perform the walk in depth first order so that we avoid marking any
|
|
// instructions live in basic blocks that are unreachable. These blocks will
|
|
// be eliminated later, along with the instructions inside.
|
|
//
|
|
for (df_iterator<Method*> BBI = df_begin(M),
|
|
BBE = df_end(M);
|
|
BBI != BBE; ++BBI) {
|
|
BasicBlock *BB = *BBI;
|
|
for (BasicBlock::iterator II = BB->begin(), EI = BB->end(); II != EI; ) {
|
|
Instruction *I = *II;
|
|
|
|
if (I->hasSideEffects() || I->getOpcode() == Instruction::Ret) {
|
|
markInstructionLive(I);
|
|
} else {
|
|
// Check to see if anything is trivially dead
|
|
if (I->use_size() == 0 && I->getType() != Type::VoidTy) {
|
|
// Remove the instruction from it's basic block...
|
|
delete BB->getInstList().remove(II);
|
|
MadeChanges = true;
|
|
continue; // Don't increment the iterator past the current slot
|
|
}
|
|
}
|
|
|
|
++II; // Increment the inst iterator if the inst wasn't deleted
|
|
}
|
|
}
|
|
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Processing work list\n";
|
|
#endif
|
|
|
|
// AliveBlocks - Set of basic blocks that we know have instructions that are
|
|
// alive in them...
|
|
//
|
|
std::set<BasicBlock*> AliveBlocks;
|
|
|
|
// Process the work list of instructions that just became live... if they
|
|
// became live, then that means that all of their operands are neccesary as
|
|
// well... make them live as well.
|
|
//
|
|
while (!WorkList.empty()) {
|
|
Instruction *I = WorkList.back(); // Get an instruction that became live...
|
|
WorkList.pop_back();
|
|
|
|
BasicBlock *BB = I->getParent();
|
|
if (AliveBlocks.count(BB) == 0) { // Basic block not alive yet...
|
|
// Mark the basic block as being newly ALIVE... and mark all branches that
|
|
// this block is control dependant on as being alive also...
|
|
//
|
|
AliveBlocks.insert(BB); // Block is now ALIVE!
|
|
cfg::DominanceFrontier::const_iterator It = CDG.find(BB);
|
|
if (It != CDG.end()) {
|
|
// Get the blocks that this node is control dependant on...
|
|
const cfg::DominanceFrontier::DomSetType &CDB = It->second;
|
|
for_each(CDB.begin(), CDB.end(), // Mark all their terminators as live
|
|
bind_obj(this, &ADCE::markTerminatorLive));
|
|
}
|
|
|
|
// If this basic block is live, then the terminator must be as well!
|
|
markTerminatorLive(BB);
|
|
}
|
|
|
|
// Loop over all of the operands of the live instruction, making sure that
|
|
// they are known to be alive as well...
|
|
//
|
|
for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op) {
|
|
if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
|
|
markInstructionLive(Operand);
|
|
}
|
|
}
|
|
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Current Method: X = Live\n";
|
|
for (Method::inst_iterator IL = M->inst_begin(); IL != M->inst_end(); ++IL) {
|
|
if (LiveSet.count(*IL)) cerr << "X ";
|
|
cerr << *IL;
|
|
}
|
|
#endif
|
|
|
|
// After the worklist is processed, recursively walk the CFG in depth first
|
|
// order, patching up references to dead blocks...
|
|
//
|
|
std::set<BasicBlock*> VisitedBlocks;
|
|
BasicBlock *EntryBlock = fixupCFG(M->front(), VisitedBlocks, AliveBlocks);
|
|
if (EntryBlock && EntryBlock != M->front()) {
|
|
if (isa<PHINode>(EntryBlock->front())) {
|
|
// Cannot make the first block be a block with a PHI node in it! Instead,
|
|
// strip the first basic block of the method to contain no instructions,
|
|
// then add a simple branch to the "real" entry node...
|
|
//
|
|
BasicBlock *E = M->front();
|
|
if (!isa<TerminatorInst>(E->front()) || // Check for an actual change...
|
|
cast<TerminatorInst>(E->front())->getNumSuccessors() != 1 ||
|
|
cast<TerminatorInst>(E->front())->getSuccessor(0) != EntryBlock) {
|
|
E->getInstList().delete_all(); // Delete all instructions in block
|
|
E->getInstList().push_back(new BranchInst(EntryBlock));
|
|
MadeChanges = true;
|
|
}
|
|
AliveBlocks.insert(E);
|
|
|
|
// Next we need to change any PHI nodes in the entry block to refer to the
|
|
// new predecessor node...
|
|
|
|
|
|
} else {
|
|
// We need to move the new entry block to be the first bb of the method.
|
|
Method::iterator EBI = find(M->begin(), M->end(), EntryBlock);
|
|
std::swap(*EBI, *M->begin());// Exchange old location with start of method
|
|
MadeChanges = true;
|
|
}
|
|
}
|
|
|
|
// Now go through and tell dead blocks to drop all of their references so they
|
|
// can be safely deleted.
|
|
//
|
|
for (Method::iterator BI = M->begin(), BE = M->end(); BI != BE; ++BI) {
|
|
BasicBlock *BB = *BI;
|
|
if (!AliveBlocks.count(BB)) {
|
|
BB->dropAllReferences();
|
|
}
|
|
}
|
|
|
|
// Now loop through all of the blocks and delete them. We can safely do this
|
|
// now because we know that there are no references to dead blocks (because
|
|
// they have dropped all of their references...
|
|
//
|
|
for (Method::iterator BI = M->begin(); BI != M->end();) {
|
|
if (!AliveBlocks.count(*BI)) {
|
|
delete M->getBasicBlocks().remove(BI);
|
|
MadeChanges = true;
|
|
continue; // Don't increment iterator
|
|
}
|
|
++BI; // Increment iterator...
|
|
}
|
|
|
|
return MadeChanges;
|
|
}
|
|
|
|
|
|
// fixupCFG - Walk the CFG in depth first order, eliminating references to
|
|
// dead blocks:
|
|
// If the BB is alive (in AliveBlocks):
|
|
// 1. Eliminate all dead instructions in the BB
|
|
// 2. Recursively traverse all of the successors of the BB:
|
|
// - If the returned successor is non-null, update our terminator to
|
|
// reference the returned BB
|
|
// 3. Return 0 (no update needed)
|
|
//
|
|
// If the BB is dead (not in AliveBlocks):
|
|
// 1. Add the BB to the dead set
|
|
// 2. Recursively traverse all of the successors of the block:
|
|
// - Only one shall return a nonnull value (or else this block should have
|
|
// been in the alive set).
|
|
// 3. Return the nonnull child, or 0 if no non-null children.
|
|
//
|
|
BasicBlock *ADCE::fixupCFG(BasicBlock *BB, std::set<BasicBlock*> &VisitedBlocks,
|
|
const std::set<BasicBlock*> &AliveBlocks) {
|
|
if (VisitedBlocks.count(BB)) return 0; // Revisiting a node? No update.
|
|
VisitedBlocks.insert(BB); // We have now visited this node!
|
|
|
|
#ifdef DEBUG_ADCE
|
|
cerr << "Fixing up BB: " << BB;
|
|
#endif
|
|
|
|
if (AliveBlocks.count(BB)) { // Is the block alive?
|
|
// Yes it's alive: loop through and eliminate all dead instructions in block
|
|
for (BasicBlock::iterator II = BB->begin(); II != BB->end()-1; ) {
|
|
Instruction *I = *II;
|
|
if (!LiveSet.count(I)) { // Is this instruction alive?
|
|
// Nope... remove the instruction from it's basic block...
|
|
delete BB->getInstList().remove(II);
|
|
MadeChanges = true;
|
|
continue; // Don't increment II
|
|
}
|
|
++II;
|
|
}
|
|
|
|
// Recursively traverse successors of this basic block.
|
|
BasicBlock::succ_iterator SI = BB->succ_begin(), SE = BB->succ_end();
|
|
for (; SI != SE; ++SI) {
|
|
BasicBlock *Succ = *SI;
|
|
BasicBlock *Repl = fixupCFG(Succ, VisitedBlocks, AliveBlocks);
|
|
if (Repl && Repl != Succ) { // We have to replace the successor
|
|
Succ->replaceAllUsesWith(Repl);
|
|
MadeChanges = true;
|
|
}
|
|
}
|
|
return BB;
|
|
} else { // Otherwise the block is dead...
|
|
BasicBlock *ReturnBB = 0; // Default to nothing live down here
|
|
|
|
// Recursively traverse successors of this basic block.
|
|
BasicBlock::succ_iterator SI = BB->succ_begin(), SE = BB->succ_end();
|
|
for (; SI != SE; ++SI) {
|
|
BasicBlock *RetBB = fixupCFG(*SI, VisitedBlocks, AliveBlocks);
|
|
if (RetBB) {
|
|
assert(ReturnBB == 0 && "One one live child allowed!");
|
|
ReturnBB = RetBB;
|
|
}
|
|
}
|
|
return ReturnBB; // Return the result of traversal
|
|
}
|
|
}
|
|
|
|
|
|
|
|
// doADCE - Execute the Agressive Dead Code Elimination Algorithm
|
|
//
|
|
bool AgressiveDCE::doADCE(Method *M) {
|
|
if (M->isExternal()) return false;
|
|
ADCE DCE(M);
|
|
return DCE.doADCE();
|
|
}
|