// predecessor only has one successor.
// * Eliminates PHI nodes for basic blocks with a single predecessor
// * Eliminates a basic block that only contains an unconditional branch
+// * Eliminates method prototypes that are not referenced
//
-// TODO: This should REALLY be recursive instead of iterative. Right now, we
-// scan linearly through values, removing unused ones as we go. The problem is
-// that this may cause other earlier values to become unused. To make sure that
-// we get them all, we iterate until things stop changing. Instead, when
+// TODO: This should REALLY be worklist driven instead of iterative. Right now,
+// we scan linearly through values, removing unused ones as we go. The problem
+// is that this may cause other earlier values to become unused. To make sure
+// that we get them all, we iterate until things stop changing. Instead, when
// removing a value, recheck all of its operands to see if they are now unused.
// Piece of cake, and more efficient as well.
//
//
//===----------------------------------------------------------------------===//
+#include "llvm/Transforms/Scalar/DCE.h"
#include "llvm/Module.h"
+#include "llvm/GlobalVariable.h"
#include "llvm/Method.h"
#include "llvm/BasicBlock.h"
#include "llvm/iTerminators.h"
-#include "llvm/iOther.h"
-#include "llvm/Opt/AllOpts.h"
+#include "llvm/iPHINode.h"
#include "llvm/Assembly/Writer.h"
-#include "llvm/CFG.h"
+#include "Support/STLExtras.h"
+#include <algorithm>
-using namespace cfg;
-
-struct ConstPoolDCE {
- enum { EndOffs = 0 };
- static bool isDCEable(const Value *) { return true; }
-};
-
-struct BasicBlockDCE {
- enum { EndOffs = 1 };
- static bool isDCEable(const Instruction *I) {
- return !I->hasSideEffects();
+// dceInstruction - Inspect the instruction at *BBI and figure out if it's
+// [trivially] dead. If so, remove the instruction and update the iterator
+// to point to the instruction that immediately succeeded the original
+// instruction.
+//
+bool DeadCodeElimination::dceInstruction(BasicBlock::InstListType &BBIL,
+ BasicBlock::iterator &BBI) {
+ // Look for un"used" definitions...
+ if ((*BBI)->use_empty() && !(*BBI)->hasSideEffects() &&
+ !isa<TerminatorInst>(*BBI)) {
+ delete BBIL.remove(BBI); // Bye bye
+ return true;
}
-};
-
+ return false;
+}
-template<class ValueSubclass, class ItemParentType, class DCEController>
-static bool RemoveUnusedDefs(ValueHolder<ValueSubclass, ItemParentType> &Vals,
- DCEController DCEControl) {
+static inline bool RemoveUnusedDefs(BasicBlock::InstListType &Vals) {
bool Changed = false;
- typedef ValueHolder<ValueSubclass, ItemParentType> Container;
-
- int Offset = DCEController::EndOffs;
- for (Container::iterator DI = Vals.begin(); DI != Vals.end()-Offset; ) {
- // Look for un"used" definitions...
- if ((*DI)->use_empty() && DCEController::isDCEable(*DI)) {
- // Bye bye
- //cerr << "Removing: " << *DI;
- delete Vals.remove(DI);
+ for (BasicBlock::InstListType::iterator DI = Vals.begin();
+ DI != Vals.end(); )
+ if (DeadCodeElimination::dceInstruction(Vals, DI))
Changed = true;
- } else {
- DI++;
- }
- }
+ else
+ ++DI;
return Changed;
}
// things in a basic block, if they are present.
//
static bool RemoveSingularPHIs(BasicBlock *BB) {
- pred_iterator PI(pred_begin(BB));
- if (PI == pred_end(BB) || ++PI != pred_end(BB))
+ BasicBlock::pred_iterator PI(BB->pred_begin());
+ if (PI == BB->pred_end() || ++PI != BB->pred_end())
return false; // More than one predecessor...
- Instruction *I = BB->getInstList().front();
- if (I->getInstType() != Instruction::PHINode) return false; // No PHI nodes
+ Instruction *I = BB->front();
+ if (!isa<PHINode>(I)) return false; // No PHI nodes
//cerr << "Killing PHIs from " << BB;
- //cerr << "Pred #0 = " << *pred_begin(BB);
+ //cerr << "Pred #0 = " << *BB->pred_begin();
//cerr << "Method == " << BB->getParent();
do {
- PHINode *PN = (PHINode*)I;
- assert(PN->getOperand(2) == 0 && "PHI node should only have one value!");
+ PHINode *PN = cast<PHINode>(I);
+ assert(PN->getNumOperands() == 2 && "PHI node should only have one value!");
Value *V = PN->getOperand(0);
PN->replaceAllUsesWith(V); // Replace PHI node with its single value.
- delete BB->getInstList().remove(BB->getInstList().begin());
+ delete BB->getInstList().remove(BB->begin());
- I = BB->getInstList().front();
- } while (I->getInstType() == Instruction::PHINode);
+ I = BB->front();
+ } while (isa<PHINode>(I));
return true; // Yes, we nuked at least one phi node
}
-bool DoRemoveUnusedConstants(SymTabValue *S) {
- bool Changed = false;
- ConstantPool &CP = S->getConstantPool();
- for (ConstantPool::plane_iterator PI = CP.begin(); PI != CP.end(); ++PI)
- Changed |= RemoveUnusedDefs(**PI, ConstPoolDCE());
- return Changed;
-}
-
static void ReplaceUsesWithConstant(Instruction *I) {
- // Get the method level constant pool
- ConstantPool &CP = I->getParent()->getParent()->getConstantPool();
-
- ConstPoolVal *CPV = 0;
- ConstantPool::PlaneType *P;
- if (!CP.getPlane(I->getType(), P)) { // Does plane exist?
- // Yes, is it empty?
- if (!P->empty()) CPV = P->front();
- }
-
- if (CPV == 0) { // We don't have an existing constant to reuse. Just add one.
- CPV = ConstPoolVal::getNullConstant(I->getType()); // Create a new constant
-
- // Add the new value to the constant pool...
- CP.insert(CPV);
- }
+ Constant *CPV = Constant::getNullConstant(I->getType());
// Make all users of this instruction reference the constant instead
I->replaceAllUsesWith(CPV);
}
-// RemovePredecessorFromBlock - This function is called when we are about
-// to remove a predecessor from a basic block. This function takes care of
-// removing the predecessor from the PHI nodes in BB so that after the pred
-// is removed, the number of PHI slots per bb is equal to the number of
-// predecessors.
-//
-static void RemovePredecessorFromBlock(BasicBlock *BB, BasicBlock *Pred) {
- pred_iterator PI(pred_begin(BB)), EI(pred_end(BB));
- unsigned max_idx;
-
- //cerr << "RPFB: " << Pred << "From Block: " << BB;
-
- // Loop over the rest of the predecssors until we run out, or until we find
- // out that there are more than 2 predecessors.
- for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
-
- // If there are exactly two predecessors, then we want to nuke the PHI nodes
- // altogether.
- bool NukePHIs = max_idx == 2;
- assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
-
- // Okay, now we know that we need to remove predecessor #pred_idx from all
- // PHI nodes. Iterate over each PHI node fixing them up
- BasicBlock::InstListType::iterator II(BB->getInstList().begin());
- for (; (*II)->getInstType() == Instruction::PHINode; ++II) {
- PHINode *PN = (PHINode*)*II;
- PN->removeIncomingValue(BB);
-
- if (NukePHIs) { // Destroy the PHI altogether??
- assert(PN->getOperand(1) == 0 && "PHI node should only have one value!");
- Value *V = PN->getOperand(0);
-
- PN->replaceAllUsesWith(V); // Replace PHI node with its single value.
- delete BB->getInstList().remove(II);
- }
- }
-}
-
// PropogatePredecessors - This gets "Succ" ready to have the predecessors from
// "BB". This is a little tricky because "Succ" has PHI nodes, which need to
// have extra slots added to them to hold the merge edges from BB's
-// predecessors.
+// predecessors. This function returns true (failure) if the Succ BB already
+// has a predecessor that is a predecessor of BB.
//
-// Assumption: BB is the single predecessor of Succ.
+// Assumption: Succ is the single successor for BB.
//
-static void PropogatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
- assert(BB && Succ && *pred_begin(Succ) == BB && "BB is only pred of Succ" &&
- ++pred_begin(Succ) == pred_end(Succ));
+static bool PropogatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
+ assert(*BB->succ_begin() == Succ && "Succ is not successor of BB!");
+ assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");
// If there is more than one predecessor, and there are PHI nodes in
// the successor, then we need to add incoming edges for the PHI nodes
- pred_iterator PI(pred_begin(BB));
- for (; PI != pred_end(BB); ++PI) {
- // TODO:
+ //
+ const std::vector<BasicBlock*> BBPreds(BB->pred_begin(), BB->pred_end());
+
+ // Check to see if one of the predecessors of BB is already a predecessor of
+ // Succ. If so, we cannot do the transformation!
+ //
+ for (BasicBlock::pred_iterator PI = Succ->pred_begin(), PE = Succ->pred_end();
+ PI != PE; ++PI) {
+ if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end())
+ return true;
}
+
+ BasicBlock::iterator I = Succ->begin();
+ do { // Loop over all of the PHI nodes in the successor BB
+ PHINode *PN = cast<PHINode>(*I);
+ Value *OldVal = PN->removeIncomingValue(BB);
+ assert(OldVal && "No entry in PHI for Pred BB!");
+
+ for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
+ End = BBPreds.end(); PredI != End; ++PredI) {
+ // Add an incoming value for each of the new incoming values...
+ PN->addIncoming(OldVal, *PredI);
+ }
+
+ ++I;
+ } while (isa<PHINode>(*I));
+ return false;
+}
+
+
+// SimplifyCFG - This function is used to do simplification of a CFG. For
+// example, it adjusts branches to branches to eliminate the extra hop, it
+// eliminates unreachable basic blocks, and does other "peephole" optimization
+// of the CFG. It returns true if a modification was made, and returns an
+// iterator that designates the first element remaining after the block that
+// was deleted.
+//
+// WARNING: The entry node of a method may not be simplified.
+//
+bool SimplifyCFG(Method::iterator &BBIt) {
+ BasicBlock *BB = *BBIt;
+ Method *M = BB->getParent();
+
+ assert(BB && BB->getParent() && "Block not embedded in method!");
+ assert(BB->getTerminator() && "Degenerate basic block encountered!");
+ assert(BB->getParent()->front() != BB && "Can't Simplify entry block!");
+
+
+ // Remove basic blocks that have no predecessors... which are unreachable.
+ if (BB->pred_begin() == BB->pred_end() &&
+ !BB->hasConstantReferences()) {
+ //cerr << "Removing BB: \n" << BB;
+
+ // Loop through all of our successors and make sure they know that one
+ // of their predecessors is going away.
+ for_each(BB->succ_begin(), BB->succ_end(),
+ std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));
+
+ while (!BB->empty()) {
+ Instruction *I = BB->back();
+ // If this instruction is used, replace uses with an arbitrary
+ // constant value. Because control flow can't get here, we don't care
+ // what we replace the value with. Note that since this block is
+ // unreachable, and all values contained within it must dominate their
+ // uses, that all uses will eventually be removed.
+ if (!I->use_empty()) ReplaceUsesWithConstant(I);
+
+ // Remove the instruction from the basic block
+ delete BB->getInstList().pop_back();
+ }
+ delete M->getBasicBlocks().remove(BBIt);
+ return true;
+ }
+
+ // Check to see if this block has no instructions and only a single
+ // successor. If so, replace block references with successor.
+ BasicBlock::succ_iterator SI(BB->succ_begin());
+ if (SI != BB->succ_end() && ++SI == BB->succ_end()) { // One succ?
+ if (BB->front()->isTerminator()) { // Terminator is the only instruction!
+ BasicBlock *Succ = *BB->succ_begin(); // There is exactly one successor
+ //cerr << "Killing Trivial BB: \n" << BB;
+
+ if (Succ != BB) { // Arg, don't hurt infinite loops!
+ // If our successor has PHI nodes, then we need to update them to
+ // include entries for BB's predecessors, not for BB itself.
+ // Be careful though, if this transformation fails (returns true) then
+ // we cannot do this transformation!
+ //
+ if (!isa<PHINode>(Succ->front()) ||
+ !PropogatePredecessorsForPHIs(BB, Succ)) {
+
+ BB->replaceAllUsesWith(Succ);
+ BB = M->getBasicBlocks().remove(BBIt);
+
+ if (BB->hasName() && !Succ->hasName()) // Transfer name if we can
+ Succ->setName(BB->getName());
+ delete BB; // Delete basic block
+
+ //cerr << "Method after removal: \n" << M;
+ return true;
+ }
+ }
+ }
+ }
+
+ // Merge basic blocks into their predecessor if there is only one pred,
+ // and if there is only one successor of the predecessor.
+ BasicBlock::pred_iterator PI(BB->pred_begin());
+ if (PI != BB->pred_end() && *PI != BB && // Not empty? Not same BB?
+ ++PI == BB->pred_end() && !BB->hasConstantReferences()) {
+ BasicBlock *Pred = *BB->pred_begin();
+ TerminatorInst *Term = Pred->getTerminator();
+ assert(Term != 0 && "malformed basic block without terminator!");
+
+ // Does the predecessor block only have a single successor?
+ BasicBlock::succ_iterator SI(Pred->succ_begin());
+ if (++SI == Pred->succ_end()) {
+ //cerr << "Merging: " << BB << "into: " << Pred;
+
+ // Delete the unconditianal branch from the predecessor...
+ BasicBlock::iterator DI = Pred->end();
+ assert(Pred->getTerminator() &&
+ "Degenerate basic block encountered!"); // Empty bb???
+ delete Pred->getInstList().remove(--DI); // Destroy uncond branch
+
+ // Move all definitions in the succecessor to the predecessor...
+ while (!BB->empty()) {
+ DI = BB->begin();
+ Instruction *Def = BB->getInstList().remove(DI); // Remove from front
+ Pred->getInstList().push_back(Def); // Add to end...
+ }
+
+ // Remove basic block from the method... and advance iterator to the
+ // next valid block...
+ BB = M->getBasicBlocks().remove(BBIt);
+
+ // Make all PHI nodes that refered to BB now refer to Pred as their
+ // source...
+ BB->replaceAllUsesWith(Pred);
+
+ // Inherit predecessors name if it exists...
+ if (BB->hasName() && !Pred->hasName()) Pred->setName(BB->getName());
+
+ delete BB; // You ARE the weakest link... goodbye
+ return true;
+ }
+ }
+
+ return false;
}
static bool DoDCEPass(Method *M) {
- Method::BasicBlocksType &BBs = M->getBasicBlocks();
- Method::BasicBlocksType::iterator BBIt, BBEnd = BBs.end();
- if (BBs.begin() == BBEnd) return false; // Nothing to do
+ Method::iterator BBIt, BBEnd = M->end();
+ if (M->begin() == BBEnd) return false; // Nothing to do
bool Changed = false;
// Loop through now and remove instructions that have no uses...
- for (BBIt = BBs.begin(); BBIt != BBEnd; BBIt++) {
- Changed |= RemoveUnusedDefs((*BBIt)->getInstList(), BasicBlockDCE());
+ for (BBIt = M->begin(); BBIt != BBEnd; ++BBIt) {
+ Changed |= RemoveUnusedDefs((*BBIt)->getInstList());
Changed |= RemoveSingularPHIs(*BBIt);
}
// Loop over all of the basic blocks (except the first one) and remove them
// if they are unneeded...
//
- for (BBIt = BBs.begin(), ++BBIt; BBIt != BBs.end(); ++BBIt) {
- BasicBlock *BB = *BBIt;
- assert(BB->getTerminator() && "Degenerate basic block encountered!");
-
-#if 0
- // Remove basic blocks that have no predecessors... which are unreachable.
- if (pred_begin(BB) == pred_end(BB) &&
- !BB->hasConstantPoolReferences() && 0) {
- cerr << "Removing BB: \n" << BB;
-
- // Loop through all of our successors and make sure they know that one
- // of their predecessors is going away.
- for (succ_iterator SI = succ_begin(BB), EI = succ_end(BB); SI != EI; ++SI)
- RemovePredecessorFromBlock(*SI, BB);
-
- while (!BB->getInstList().empty()) {
- Instruction *I = BB->getInstList().front();
- // If this instruction is used, replace uses with an arbitrary
- // constant value. Because control flow can't get here, we don't care
- // what we replace the value with.
- if (!I->use_empty()) ReplaceUsesWithConstant(I);
-
- // Remove the instruction from the basic block
- delete BB->getInstList().remove(BB->getInstList().begin());
- }
- delete BBs.remove(BBIt);
- --BBIt; // remove puts use on the next block, we want the previous one
+ for (BBIt = M->begin(), ++BBIt; BBIt != M->end(); ) {
+ if (SimplifyCFG(BBIt)) {
Changed = true;
- continue;
- }
-
- // Check to see if this block has no instructions and only a single
- // successor. If so, replace block references with successor.
- succ_iterator SI(succ_begin(BB));
- if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
- Instruction *I = BB->getInstList().front();
- if (I->isTerminator()) { // Terminator is the only instruction!
-
- if (Succ->getInstList().front()->getInstType() == Instruction::PHINode){
- // Add entries to the PHI nodes so that the PHI nodes have the right
- // number of entries...
- PropogatePredecessorsForPHIs(BB, Succ);
- }
-
- BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
- BB->replaceAllUsesWith(Succ);
- cerr << "Killing Trivial BB: \n" << BB;
-
- BB = BBs.remove(BBIt);
- --BBIt; // remove puts use on the next block, we want the previous one
-
- if (BB->hasName() && !Succ->hasName()) // Transfer name if we can
- Succ->setName(BB->getName());
- delete BB; // Delete basic block
-
- cerr << "Method after removal: \n" << M;
- Changed = true;
- continue;
- }
- }
-#endif
-
- // Merge basic blocks into their predecessor if there is only one pred,
- // and if there is only one successor of the predecessor.
- pred_iterator PI(pred_begin(BB));
- if (PI != pred_end(BB) && *PI != BB && // Not empty? Not same BB?
- ++PI == pred_end(BB) && !BB->hasConstantPoolReferences()) {
- BasicBlock *Pred = *pred_begin(BB);
- TerminatorInst *Term = Pred->getTerminator();
- assert(Term != 0 && "malformed basic block without terminator!");
-
- // Does the predecessor block only have a single successor?
- succ_iterator SI(succ_begin(Pred));
- if (++SI == succ_end(Pred)) {
- //cerr << "Merging: " << BB << "into: " << Pred;
-
- // Delete the unconditianal branch from the predecessor...
- BasicBlock::InstListType::iterator DI = Pred->getInstList().end();
- assert(Pred->getTerminator() &&
- "Degenerate basic block encountered!"); // Empty bb???
- delete Pred->getInstList().remove(--DI); // Destroy uncond branch
-
- // Move all definitions in the succecessor to the predecessor...
- while (!BB->getInstList().empty()) {
- DI = BB->getInstList().begin();
- Instruction *Def = BB->getInstList().remove(DI); // Remove from front
- Pred->getInstList().push_back(Def); // Add to end...
- }
-
- // Remove basic block from the method... and advance iterator to the
- // next valid block...
- BB = BBs.remove(BBIt);
- --BBIt; // remove puts us on the NEXT bb. We want the prev BB
- Changed = true;
-
- // Make all PHI nodes that refered to BB now refer to Pred as their
- // source...
- BB->replaceAllUsesWith(Pred);
-
- // Inherit predecessors name if it exists...
- if (BB->hasName() && !Pred->hasName()) Pred->setName(BB->getName());
-
- // You ARE the weakest link... goodbye
- delete BB;
-
- //WriteToVCG(M, "MergedInto");
- }
+ } else {
+ ++BBIt;
}
}
- // Remove unused constants
- Changed |= DoRemoveUnusedConstants(M);
return Changed;
}
// It is possible that we may require multiple passes over the code to fully
// eliminate dead code. Iterate until we are done.
//
-bool DoDeadCodeElimination(Method *M) {
+bool DeadCodeElimination::doDCE(Method *M) {
bool Changed = false;
while (DoDCEPass(M)) Changed = true;
return Changed;
}
-bool DoDeadCodeElimination(Module *C) {
- bool Val = ApplyOptToAllMethods(C, DoDeadCodeElimination);
- while (DoRemoveUnusedConstants(C)) Val = true;
- return Val;
+bool DeadCodeElimination::RemoveUnusedGlobalValues(Module *Mod) {
+ bool Changed = false;
+
+ for (Module::iterator MI = Mod->begin(); MI != Mod->end(); ) {
+ Method *Meth = *MI;
+ if (Meth->isExternal() && Meth->use_size() == 0) {
+ // No references to prototype?
+ //cerr << "Removing method proto: " << Meth->getName() << endl;
+ delete Mod->getMethodList().remove(MI); // Remove prototype
+ // Remove moves iterator to point to the next one automatically
+ Changed = true;
+ } else {
+ ++MI; // Skip prototype in use.
+ }
+ }
+
+ for (Module::giterator GI = Mod->gbegin(); GI != Mod->gend(); ) {
+ GlobalVariable *GV = *GI;
+ if (!GV->hasInitializer() && GV->use_size() == 0) {
+ // No references to uninitialized global variable?
+ //cerr << "Removing global var: " << GV->getName() << endl;
+ delete Mod->getGlobalList().remove(GI);
+ // Remove moves iterator to point to the next one automatically
+ Changed = true;
+ } else {
+ ++GI;
+ }
+ }
+
+ return Changed;
}
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