-//===- ConstantProp.cpp - Code to perform Constant Propogation ------------===//
+//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
//
-// This file implements constant propogation and merging:
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements constant propagation 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.
+// * Converts instructions like "add int 1, 2" into 3
//
// 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.
+// to run a DIE pass sometime after running this pass.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Optimizations/ConstantProp.h"
-#include "llvm/Optimizations/ConstantHandling.h"
-#include "llvm/Module.h"
-#include "llvm/Method.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iOther.h"
-#include "llvm/ConstantVals.h"
-
-inline static bool
-ConstantFoldUnaryInst(BasicBlock *BB, BasicBlock::iterator &II,
- UnaryOperator *Op, Constant *D) {
- Constant *ReplaceWith =
- opt::ConstantFoldUnaryInstruction(Op->getOpcode(), D);
-
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // 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(II);
-
- // The new constant inherits the old name of the operator...
- if (Op->hasName())
- ReplaceWith->setName(Op->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the operator now...
- delete Op;
- return true;
-}
-
-inline static bool
-ConstantFoldCast(BasicBlock *BB, BasicBlock::iterator &II,
- CastInst *CI, Constant *D) {
- Constant *ReplaceWith =
- opt::ConstantFoldCastInstruction(D, CI->getType());
-
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // Replaces all of the uses of a variable with uses of the constant.
- CI->replaceAllUsesWith(ReplaceWith);
-
- // Remove the cast from the list of definitions...
- CI->getParent()->getInstList().remove(II);
-
- // The new constant inherits the old name of the cast...
- if (CI->hasName())
- ReplaceWith->setName(CI->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the cast now...
- delete CI;
- return true;
-}
-
-inline static bool
-ConstantFoldBinaryInst(BasicBlock *BB, BasicBlock::iterator &II,
- BinaryOperator *Op,
- Constant *D1, Constant *D2) {
- Constant *ReplaceWith =
- opt::ConstantFoldBinaryInstruction(Op->getOpcode(), D1, D2);
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // 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(II);
-
- // The new constant inherits the old name of the operator...
- if (Op->hasName())
- ReplaceWith->setName(Op->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the operator now...
- delete Op;
- return true;
-}
-
-// ConstantFoldTerminator - If a terminator instruction is predicated on a
-// constant value, convert it into an unconditional branch to the constant
-// destination.
-//
-bool opt::ConstantFoldTerminator(TerminatorInst *T) {
- // Branch - See if we are conditional jumping on constant
- if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
- if (BI->isUnconditional()) return false; // Can't optimize uncond branch
- BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
- BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
-
- if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
- // Are we branching on constant?
- // YES. Change to unconditional branch...
- BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
- BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
-
- //cerr << "Method: " << T->getParent()->getParent()
- // << "\nRemoving branch from " << T->getParent()
- // << "\n\nTo: " << OldDest << endl;
+#define DEBUG_TYPE "constprop"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Constant.h"
+#include "llvm/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/InstIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include <set>
+using namespace llvm;
- // Let the basic block know that we are letting go of it. Based on this,
- // it will adjust it's PHI nodes.
- assert(BI->getParent() && "Terminator not inserted in block!");
- OldDest->removePredecessor(BI->getParent());
+STATISTIC(NumInstKilled, "Number of instructions killed");
- // Set the unconditional destination, and change the insn to be an
- // unconditional branch.
- BI->setUnconditionalDest(Destination);
- return true;
- }
-#if 0
- // FIXME: TODO: This doesn't work if the destination has PHI nodes with
- // different incoming values on each branch!
- //
- else if (Dest2 == Dest1) { // Conditional branch to same location?
- // This branch matches something like this:
- // br bool %cond, label %Dest, label %Dest
- // and changes it into: br label %Dest
+namespace {
+ struct ConstantPropagation : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ ConstantPropagation() : FunctionPass(&ID) {}
- // Let the basic block know that we are letting go of one copy of it.
- assert(BI->getParent() && "Terminator not inserted in block!");
- Dest1->removePredecessor(BI->getParent());
+ bool runOnFunction(Function &F);
- // Change a conditional branch to unconditional.
- BI->setUnconditionalDest(Dest1);
- return true;
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
}
-#endif
- }
- return false;
+ };
}
-// ConstantFoldInstruction - If an instruction references constants, try to fold
-// them together...
-//
-bool opt::ConstantPropogation::doConstantPropogation(BasicBlock *BB,
- BasicBlock::iterator &II) {
- Instruction *Inst = *II;
- if (isa<BinaryOperator>(Inst)) {
- Constant *D1 = dyn_cast<Constant>(Inst->getOperand(0));
- Constant *D2 = dyn_cast<Constant>(Inst->getOperand(1));
+char ConstantPropagation::ID = 0;
+INITIALIZE_PASS(ConstantPropagation, "constprop",
+ "Simple constant propagation", false, false);
- if (D1 && D2)
- return ConstantFoldBinaryInst(BB, II, cast<BinaryOperator>(Inst), D1, D2);
-
- } else if (CastInst *CI = dyn_cast<CastInst>(Inst)) {
- Constant *D = dyn_cast<Constant>(CI->getOperand(0));
- if (D) return ConstantFoldCast(BB, II, CI, D);
-
- } else if (UnaryOperator *UInst = dyn_cast<UnaryOperator>(Inst)) {
- Constant *D = dyn_cast<Constant>(UInst->getOperand(0));
- if (D) return ConstantFoldUnaryInst(BB, II, UInst, D);
- } else if (TerminatorInst *TInst = dyn_cast<TerminatorInst>(Inst)) {
- return opt::ConstantFoldTerminator(TInst);
-
- } else if (PHINode *PN = dyn_cast<PHINode>(Inst)) {
- // If it's a PHI node and only has one operand
- // Then replace it directly with that operand.
- assert(PN->getNumOperands() && "PHI Node must have at least one operand!");
- if (PN->getNumOperands() == 1) { // 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);
- if (PN->hasName()) // Inherit PHINode name
- V->setName(PN->getName(), BB->getParent()->getSymbolTableSure());
- delete PN; // Finally, delete the node...
- return true;
- }
- }
- return false;
+FunctionPass *llvm::createConstantPropagationPass() {
+ return new ConstantPropagation();
}
-// 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;
- for (Method::iterator BBI = M->begin(); BBI != M->end(); ++BBI) {
- BasicBlock *BB = *BBI;
- for (BasicBlock::iterator I = BB->begin(); I != BB->end(); )
- if (opt::ConstantPropogation::doConstantPropogation(BB, I))
- SomethingChanged = true;
- else
- ++I;
+bool ConstantPropagation::runOnFunction(Function &F) {
+ // Initialize the worklist to all of the instructions ready to process...
+ std::set<Instruction*> WorkList;
+ for(inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
+ WorkList.insert(&*i);
}
- return SomethingChanged;
-}
-
-
-// returns whether or not the underlying method was modified
-//
-bool opt::ConstantPropogation::doConstantPropogation(Method *M) {
- bool Modified = false;
-
- // Fold constants until we make no progress...
- while (DoConstPropPass(M)) Modified = true;
-
- return Modified;
+ bool Changed = false;
+
+ while (!WorkList.empty()) {
+ Instruction *I = *WorkList.begin();
+ WorkList.erase(WorkList.begin()); // Get an element from the worklist...
+
+ if (!I->use_empty()) // Don't muck with dead instructions...
+ if (Constant *C = ConstantFoldInstruction(I)) {
+ // Add all of the users of this instruction to the worklist, they might
+ // be constant propagatable now...
+ for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE; ++UI)
+ WorkList.insert(cast<Instruction>(*UI));
+
+ // Replace all of the uses of a variable with uses of the constant.
+ I->replaceAllUsesWith(C);
+
+ // Remove the dead instruction.
+ WorkList.erase(I);
+ I->eraseFromParent();
+
+ // We made a change to the function...
+ Changed = true;
+ ++NumInstKilled;
+ }
+ }
+ return Changed;
}
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