| //===-- Local.cpp - Functions to perform local transformations ------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This family of functions perform various local transformations to the |
| // program. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/iTerminators.h" |
| #include "llvm/iOperators.h" |
| #include "llvm/ConstantHandling.h" |
| |
| namespace llvm { |
| |
| //===----------------------------------------------------------------------===// |
| // Local constant propagation... |
| // |
| |
| // ConstantFoldInstruction - If an instruction references constants, try to fold |
| // them together... |
| // |
| bool doConstantPropagation(BasicBlock::iterator &II) { |
| if (Constant *C = ConstantFoldInstruction(II)) { |
| // Replaces all of the uses of a variable with uses of the constant. |
| II->replaceAllUsesWith(C); |
| |
| // Remove the instruction from the basic block... |
| II = II->getParent()->getInstList().erase(II); |
| return true; |
| } |
| |
| return false; |
| } |
| |
| // ConstantFoldTerminator - If a terminator instruction is predicated on a |
| // constant value, convert it into an unconditional branch to the constant |
| // destination. |
| // |
| bool ConstantFoldTerminator(BasicBlock *BB) { |
| TerminatorInst *T = BB->getTerminator(); |
| |
| // 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 << "Function: " << T->getParent()->getParent() |
| // << "\nRemoving branch from " << T->getParent() |
| // << "\n\nTo: " << OldDest << endl; |
| |
| // 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; |
| } |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { |
| // If we are switching on a constant, we can convert the switch into a |
| // single branch instruction! |
| ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); |
| BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest |
| BasicBlock *DefaultDest = TheOnlyDest; |
| assert(TheOnlyDest == SI->getDefaultDest() && |
| "Default destination is not successor #0?"); |
| |
| // Figure out which case it goes to... |
| for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { |
| // Found case matching a constant operand? |
| if (SI->getSuccessorValue(i) == CI) { |
| TheOnlyDest = SI->getSuccessor(i); |
| break; |
| } |
| |
| // Check to see if this branch is going to the same place as the default |
| // dest. If so, eliminate it as an explicit compare. |
| if (SI->getSuccessor(i) == DefaultDest) { |
| // Remove this entry... |
| DefaultDest->removePredecessor(SI->getParent()); |
| SI->removeCase(i); |
| --i; --e; // Don't skip an entry... |
| continue; |
| } |
| |
| // Otherwise, check to see if the switch only branches to one destination. |
| // We do this by reseting "TheOnlyDest" to null when we find two non-equal |
| // destinations. |
| if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0; |
| } |
| |
| if (CI && !TheOnlyDest) { |
| // Branching on a constant, but not any of the cases, go to the default |
| // successor. |
| TheOnlyDest = SI->getDefaultDest(); |
| } |
| |
| // If we found a single destination that we can fold the switch into, do so |
| // now. |
| if (TheOnlyDest) { |
| // Insert the new branch.. |
| new BranchInst(TheOnlyDest, SI); |
| BasicBlock *BB = SI->getParent(); |
| |
| // Remove entries from PHI nodes which we no longer branch to... |
| for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { |
| // Found case matching a constant operand? |
| BasicBlock *Succ = SI->getSuccessor(i); |
| if (Succ == TheOnlyDest) |
| TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest |
| else |
| Succ->removePredecessor(BB); |
| } |
| |
| // Delete the old switch... |
| BB->getInstList().erase(SI); |
| return true; |
| } else if (SI->getNumSuccessors() == 2) { |
| // Otherwise, we can fold this switch into a conditional branch |
| // instruction if it has only one non-default destination. |
| Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(), |
| SI->getSuccessorValue(1), "cond", SI); |
| // Insert the new branch... |
| new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI); |
| |
| // Delete the old switch... |
| SI->getParent()->getInstList().erase(SI); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Local dead code elimination... |
| // |
| |
| bool isInstructionTriviallyDead(Instruction *I) { |
| return I->use_empty() && !I->mayWriteToMemory() && !isa<TerminatorInst>(I); |
| } |
| |
| // 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 dceInstruction(BasicBlock::iterator &BBI) { |
| // Look for un"used" definitions... |
| if (isInstructionTriviallyDead(BBI)) { |
| BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye |
| return true; |
| } |
| return false; |
| } |
| |
| } // End llvm namespace |