-//===- 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/iOther.h"
-#include "llvm/ConstPoolVals.h"
-#include "llvm/ConstantPool.h"
-
-// Merge identical constant values in the constant pool.
-//
-// TODO: We can do better than this simplistic N^2 algorithm...
-//
-bool opt::DoConstantPoolMerging(Method *M) {
- return DoConstantPoolMerging(M->getConstantPool());
-}
-
-bool opt::DoConstantPoolMerging(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
- }
- }
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include <set>
+using namespace llvm;
+
+#define DEBUG_TYPE "constprop"
+
+STATISTIC(NumInstKilled, "Number of instructions killed");
+
+namespace {
+ struct ConstantPropagation : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ ConstantPropagation() : FunctionPass(ID) {
+ initializeConstantPropagationPass(*PassRegistry::getPassRegistry());
}
- }
- return Modified;
-}
-
-inline static bool
-ConstantFoldUnaryInst(Method *M, Method::inst_iterator &DI,
- UnaryOperator *Op, ConstPoolVal *D) {
- ConstPoolVal *ReplaceWith =
- opt::ConstantFoldUnaryInstruction(Op->getOpcode(), D);
-
- 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 =
- opt::ConstantFoldBinaryInstruction(Op->getOpcode(), D1, D2);
- 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;
-}
-
-// 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 (T->getOpcode() == Instruction::Br) {
- BranchInst *BI = (BranchInst*)T;
- if (BI->isUnconditional()) return false; // Can't optimize uncond branch
- BasicBlock *Dest1 = BI->getOperand(0)->castBasicBlockAsserting();
- BasicBlock *Dest2 = BI->getOperand(1)->castBasicBlockAsserting();
-
- if (BI->getCondition()->isConstant()) { // Are we branching on constant?
- // YES. Change to unconditional branch...
- ConstPoolBool *Cond = (ConstPoolBool*)BI->getCondition();
- 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;
+ bool runOnFunction(Function &F) override;
- // 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());
-
- // Set the unconditional destination, and change the insn to be an
- // unconditional branch.
- BI->setUnconditionalDest(Destination);
- return true;
- } 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
-
- // 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());
-
- // Change a conditional branch to unconditional.
- BI->setUnconditionalDest(Dest1);
- return true;
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
}
- }
- 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()) {
- ConstPoolVal *D1 = Inst->getOperand(0)->castConstant();
- ConstPoolVal *D2 = Inst->getOperand(1)->castConstant();
-
- if (D1 && D2)
- return ConstantFoldBinaryInst(M, II, (BinaryOperator*)Inst, D1, D2);
+char ConstantPropagation::ID = 0;
+INITIALIZE_PASS_BEGIN(ConstantPropagation, "constprop",
+ "Simple constant propagation", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(ConstantPropagation, "constprop",
+ "Simple constant propagation", false, false)
- } else if (Inst->isUnaryOp()) {
- ConstPoolVal *D = Inst->getOperand(0)->castConstant();
- if (D) return ConstantFoldUnaryInst(M, II, (UnaryOperator*)Inst, D);
- } else if (Inst->isTerminator()) {
- return opt::ConstantFoldTerminator((TerminatorInst*)Inst);
-
- } else if (Inst->isPHINode()) {
- 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->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.getInstructionIterator());
- if (PN->hasName()) V->setName(PN->getName()); // Inherit PHINode name
- 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;
-
-#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
- for (Method::iterator BBIt = M->begin(); BBIt != M->end(); ++BBIt) {
- BasicBlock *BB = *BBIt;
-
- reduce_apply_bool(BB->begin(), BB->end(),
- bind1st(ConstantFoldInstruction, M));
+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);
}
-#endif
- return SomethingChanged;
-}
-
-
-// returns true on failure, false on success...
-//
-bool opt::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 |= DoConstantPoolMerging(M->getConstantPool());
-
- return Modified;
+ bool Changed = false;
+ const DataLayout &DL = F.getParent()->getDataLayout();
+ TargetLibraryInfo *TLI =
+ &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+
+ 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, DL, TLI)) {
+ // Add all of the users of this instruction to the worklist, they might
+ // be constant propagatable now...
+ for (User *U : I->users())
+ WorkList.insert(cast<Instruction>(U));
+
+ // 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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