-//===- ADCE.cpp - Code to perform agressive dead code elimination ---------===//
+//===- ADCE.cpp - Code to perform aggressive dead code elimination --------===//
//
-// This file implements "agressive" dead code elimination. ADCE is DCe where
+// This file implements "aggressive" 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/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/Writer.h"
//===----------------------------------------------------------------------===//
// ADCE Class
//
-// This class does all of the work of Agressive Dead Code Elimination.
+// This class does all of the work of Aggressive Dead Code Elimination.
// It's public interface consists of a constructor and a doADCE() method.
//
class ADCE : public FunctionPass {
public:
const char *getPassName() const { return "Aggressive Dead Code Elimination"; }
- // doADCE - Execute the Agressive Dead Code Elimination Algorithm
+ // doADCE - Execute the Aggressive Dead Code Elimination Algorithm
//
virtual bool runOnFunction(Function *F) {
Func = F; MadeChanges = false;
// The implementation of this class
//
private:
- // doADCE() - Run the Agressive Dead Code Elimination algorithm, returning
+ // doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning
// true if the function was modified.
//
void doADCE(DominanceFrontier &CDG);
} // End of anonymous namespace
-Pass *createAgressiveDCEPass() {
+Pass *createAggressiveDCEPass() {
return new ADCE();
}
-// doADCE() - Run the Agressive Dead Code Elimination algorithm, returning
+// doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning
// true if the function was modified.
//
void ADCE::doADCE(DominanceFrontier &CDG) {
if (I->hasSideEffects() || I->getOpcode() == Instruction::Ret) {
markInstructionLive(I);
+ ++II; // Increment the inst iterator if the inst wasn't deleted
+ } else if (isInstructionTriviallyDead(I)) {
+ // Remove the instruction from it's basic block...
+ delete BB->getInstList().remove(II);
+ MadeChanges = true;
} 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
}
-
- ++II; // Increment the inst iterator if the inst wasn't deleted
}
}
// 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) {
+ for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
markInstructionLive(Operand);
- }
}
#ifdef DEBUG_ADCE
//
std::set<BasicBlock*> VisitedBlocks;
BasicBlock *EntryBlock = fixupCFG(Func->front(), VisitedBlocks, AliveBlocks);
- if (EntryBlock && EntryBlock != Func->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 function to contain no instructions,
- // then add a simple branch to the "real" entry node...
- //
- BasicBlock *E = Func->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 function
- Function::iterator EBI = find(Func->begin(), Func->end(), EntryBlock);
- std::swap(*EBI, *Func->begin()); // Exchange old location with start of fn
- MadeChanges = true;
- }
- }
// Now go through and tell dead blocks to drop all of their references so they
- // can be safely deleted.
+ // can be safely deleted. Also, as we are doing so, if the block has
+ // successors that are still live (and that have PHI nodes in them), remove
+ // the entry for this block from the phi nodes.
//
for (Function::iterator BI = Func->begin(), BE = Func->end(); BI != BE; ++BI){
BasicBlock *BB = *BI;
if (!AliveBlocks.count(BB)) {
+ // Remove entries from successors PHI nodes if they are still alive...
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+ if (AliveBlocks.count(*SI)) { // Only if the successor is alive...
+ BasicBlock *Succ = *SI;
+ for (BasicBlock::iterator I = Succ->begin();// Loop over all PHI nodes
+ PHINode *PN = dyn_cast<PHINode>(*I); ++I)
+ PN->removeIncomingValue(BB); // Remove value for this block
+ }
+
BB->dropAllReferences();
}
}
+ cerr << "Before Deleting Blocks: " << Func;
+
// 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...
}
++BI; // Increment iterator...
}
+
+ if (EntryBlock && EntryBlock != Func->front()) {
+ // We need to move the new entry block to be the first bb of the function
+ Function::iterator EBI = find(Func->begin(), Func->end(), EntryBlock);
+ std::swap(*EBI, *Func->begin()); // Exchange old location with start of fn
+ }
+
+ while (PHINode *PN = dyn_cast<PHINode>(EntryBlock->front())) {
+ assert(PN->getNumIncomingValues() == 1 &&
+ "Can only have a single incoming value at this point...");
+ // The incoming value must be outside of the scope of the function, a
+ // global variable, constant or parameter maybe...
+ //
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+
+ // Nuke the phi node...
+ delete EntryBlock->getInstList().remove(EntryBlock->begin());
+ }
}
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?
+ for (BasicBlock::iterator II = BB->begin(); II != BB->end()-1; )
+ if (!LiveSet.count(*II)) { // 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
+ } else {
+ ++II;
}
- ++II;
- }
// Recursively traverse successors of this basic block.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) {
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) {
BasicBlock *RetBB = fixupCFG(*SI, VisitedBlocks, AliveBlocks);
if (RetBB) {
- assert(ReturnBB == 0 && "One one live child allowed!");
+ assert(ReturnBB == 0 && "At most one live child allowed!");
ReturnBB = RetBB;
}
}
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