lib/Transforms/Utils/Local.cpp - llvm - Git at Google

 //===-- 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/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Instructions.h"
 #include "llvm/Intrinsics.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
 #include <cerrno>
 #include <cmath>
 using namespace llvm;

 //===----------------------------------------------------------------------===//
 //  Local constant propagation...
 //

 /// doConstantPropagation - If an instruction references constants, try to fold
 /// them together...
 ///
 bool llvm::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;
 }

 /// ConstantFoldInstruction - Attempt to constant fold the specified
 /// instruction.  If successful, the constant result is returned, if not, null
 /// is returned.  Note that this function can only fail when attempting to fold
 /// instructions like loads and stores, which have no constant expression form.
 ///
 Constant *llvm::ConstantFoldInstruction(Instruction *I) {
   if (PHINode *PN = dyn_cast<PHINode>(I)) {
     if (PN->getNumIncomingValues() == 0)
       return Constant::getNullValue(PN->getType());

     Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
     if (Result == 0) return 0;

     // Handle PHI nodes specially here...
     for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
       if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
         return 0;   // Not all the same incoming constants...

     // If we reach here, all incoming values are the same constant.
     return Result;
   } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
     if (Function *F = CI->getCalledFunction())
       if (canConstantFoldCallTo(F)) {
         std::vector<Constant*> Args;
         for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
           if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
             Args.push_back(Op);
           else
             return 0;
         return ConstantFoldCall(F, Args);
       }
     return 0;
   }

   Constant *Op0 = 0, *Op1 = 0;
   switch (I->getNumOperands()) {
   default:
   case 2:
     Op1 = dyn_cast<Constant>(I->getOperand(1));
     if (Op1 == 0) return 0;        // Not a constant?, can't fold
   case 1:
     Op0 = dyn_cast<Constant>(I->getOperand(0));
     if (Op0 == 0) return 0;        // Not a constant?, can't fold
     break;
   case 0: return 0;
   }

   if (isa<BinaryOperator>(I) || isa<ShiftInst>(I))
     return ConstantExpr::get(I->getOpcode(), Op0, Op1);

   switch (I->getOpcode()) {
   default: return 0;
   case Instruction::Cast:
     return ConstantExpr::getCast(Op0, I->getType());
   case Instruction::Select:
     if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
       return ConstantExpr::getSelect(Op0, Op1, Op2);
     return 0;
   case Instruction::GetElementPtr:
     std::vector<Constant*> IdxList;
     IdxList.reserve(I->getNumOperands()-1);
     if (Op1) IdxList.push_back(Op1);
     for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
       if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
         IdxList.push_back(C);
       else
         return 0;  // Non-constant operand
     return ConstantExpr::getGetElementPtr(Op0, IdxList);
   }
 }

 // ConstantFoldTerminator - If a terminator instruction is predicated on a
 // constant value, convert it into an unconditional branch to the constant
 // destination.
 //
 bool llvm::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;
 }

 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
 /// getelementptr constantexpr, return the constant value being addressed by the
 /// constant expression, or null if something is funny and we can't decide.
 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
                                                        ConstantExpr *CE) {
   if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
     return 0;  // Do not allow stepping over the value!

   // Loop over all of the operands, tracking down which value we are
   // addressing...
   gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
   for (++I; I != E; ++I)
     if (const StructType *STy = dyn_cast<StructType>(*I)) {
       ConstantUInt *CU = cast<ConstantUInt>(I.getOperand());
       assert(CU->getValue() < STy->getNumElements() &&
              "Struct index out of range!");
       unsigned El = (unsigned)CU->getValue();
       if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
         C = CS->getOperand(El);
       } else if (isa<ConstantAggregateZero>(C)) {
         C = Constant::getNullValue(STy->getElementType(El));
       } else if (isa<UndefValue>(C)) {
         C = UndefValue::get(STy->getElementType(El));
       } else {
         return 0;
       }
     } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
       const ArrayType *ATy = cast<ArrayType>(*I);
       if ((uint64_t)CI->getRawValue() >= ATy->getNumElements()) return 0;
       if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
         C = CA->getOperand((unsigned)CI->getRawValue());
       else if (isa<ConstantAggregateZero>(C))
         C = Constant::getNullValue(ATy->getElementType());
       else if (isa<UndefValue>(C))
         C = UndefValue::get(ATy->getElementType());
       else
         return 0;
     } else {
       return 0;
     }
   return C;
 }


 //===----------------------------------------------------------------------===//
 //  Local dead code elimination...
 //

 bool llvm::isInstructionTriviallyDead(Instruction *I) {
   if (!I->use_empty() || isa<TerminatorInst>(I)) return false;

   if (!I->mayWriteToMemory()) return true;

   if (CallInst *CI = dyn_cast<CallInst>(I))
     if (Function *F = CI->getCalledFunction())
       switch (F->getIntrinsicID()) {
       default: break;
       case Intrinsic::returnaddress:
       case Intrinsic::frameaddress:
       case Intrinsic::isunordered:
       case Intrinsic::ctpop:
       case Intrinsic::ctlz:
       case Intrinsic::cttz:
       case Intrinsic::sqrt:
         return true;             // These intrinsics have no side effects.
       }
   return false;
 }

 // 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 llvm::dceInstruction(BasicBlock::iterator &BBI) {
   // Look for un"used" definitions...
   if (isInstructionTriviallyDead(BBI)) {
     BBI = BBI->getParent()->getInstList().erase(BBI);   // Bye bye
     return true;
   }
   return false;
 }
	//===-- 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/Constants.h"
	#include "llvm/DerivedTypes.h"
	#include "llvm/Instructions.h"
	#include "llvm/Intrinsics.h"
	#include "llvm/Analysis/ConstantFolding.h"
	#include "llvm/Support/GetElementPtrTypeIterator.h"
	#include "llvm/Support/MathExtras.h"
	#include <cerrno>
	#include <cmath>
	using namespace llvm;

	//===----------------------------------------------------------------------===//
	// Local constant propagation...
	//

	/// doConstantPropagation - If an instruction references constants, try to fold
	/// them together...
	///
	bool llvm::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;
	}

	/// ConstantFoldInstruction - Attempt to constant fold the specified
	/// instruction. If successful, the constant result is returned, if not, null
	/// is returned. Note that this function can only fail when attempting to fold
	/// instructions like loads and stores, which have no constant expression form.
	///
	Constant llvm::ConstantFoldInstruction(Instruction I) {
	if (PHINode *PN = dyn_cast<PHINode>(I)) {
	if (PN->getNumIncomingValues() == 0)
	return Constant::getNullValue(PN->getType());

	Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
	if (Result == 0) return 0;

	// Handle PHI nodes specially here...
	for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
	if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
	return 0; // Not all the same incoming constants...

	// If we reach here, all incoming values are the same constant.
	return Result;
	} else if (CallInst *CI = dyn_cast<CallInst>(I)) {
	if (Function *F = CI->getCalledFunction())
	if (canConstantFoldCallTo(F)) {
	std::vector<Constant*> Args;
	for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
	if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
	Args.push_back(Op);
	else
	return 0;
	return ConstantFoldCall(F, Args);
	}
	return 0;
	}

	Constant Op0 = 0, Op1 = 0;
	switch (I->getNumOperands()) {
	default:
	case 2:
	Op1 = dyn_cast<Constant>(I->getOperand(1));
	if (Op1 == 0) return 0; // Not a constant?, can't fold
	case 1:
	Op0 = dyn_cast<Constant>(I->getOperand(0));
	if (Op0 == 0) return 0; // Not a constant?, can't fold
	break;
	case 0: return 0;
	}

	if (isa<BinaryOperator>(I) \|\| isa<ShiftInst>(I))
	return ConstantExpr::get(I->getOpcode(), Op0, Op1);

	switch (I->getOpcode()) {
	default: return 0;
	case Instruction::Cast:
	return ConstantExpr::getCast(Op0, I->getType());
	case Instruction::Select:
	if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
	return ConstantExpr::getSelect(Op0, Op1, Op2);
	return 0;
	case Instruction::GetElementPtr:
	std::vector<Constant*> IdxList;
	IdxList.reserve(I->getNumOperands()-1);
	if (Op1) IdxList.push_back(Op1);
	for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
	if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
	IdxList.push_back(C);
	else
	return 0; // Non-constant operand
	return ConstantExpr::getGetElementPtr(Op0, IdxList);
	}
	}

	// ConstantFoldTerminator - If a terminator instruction is predicated on a
	// constant value, convert it into an unconditional branch to the constant
	// destination.
	//
	bool llvm::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;
	}

	/// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
	/// getelementptr constantexpr, return the constant value being addressed by the
	/// constant expression, or null if something is funny and we can't decide.
	Constant llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant C,
	ConstantExpr *CE) {
	if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
	return 0; // Do not allow stepping over the value!

	// Loop over all of the operands, tracking down which value we are
	// addressing...
	gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
	for (++I; I != E; ++I)
	if (const StructType STy = dyn_cast<StructType>(I)) {
	ConstantUInt *CU = cast<ConstantUInt>(I.getOperand());
	assert(CU->getValue() < STy->getNumElements() &&
	"Struct index out of range!");
	unsigned El = (unsigned)CU->getValue();
	if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
	C = CS->getOperand(El);
	} else if (isa<ConstantAggregateZero>(C)) {
	C = Constant::getNullValue(STy->getElementType(El));
	} else if (isa<UndefValue>(C)) {
	C = UndefValue::get(STy->getElementType(El));
	} else {
	return 0;
	}
	} else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
	const ArrayType ATy = cast<ArrayType>(I);
	if ((uint64_t)CI->getRawValue() >= ATy->getNumElements()) return 0;
	if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
	C = CA->getOperand((unsigned)CI->getRawValue());
	else if (isa<ConstantAggregateZero>(C))
	C = Constant::getNullValue(ATy->getElementType());
	else if (isa<UndefValue>(C))
	C = UndefValue::get(ATy->getElementType());
	else
	return 0;
	} else {
	return 0;
	}
	return C;
	}


	//===----------------------------------------------------------------------===//
	// Local dead code elimination...
	//

	bool llvm::isInstructionTriviallyDead(Instruction *I) {
	if (!I->use_empty() \|\| isa<TerminatorInst>(I)) return false;

	if (!I->mayWriteToMemory()) return true;

	if (CallInst *CI = dyn_cast<CallInst>(I))
	if (Function *F = CI->getCalledFunction())
	switch (F->getIntrinsicID()) {
	default: break;
	case Intrinsic::returnaddress:
	case Intrinsic::frameaddress:
	case Intrinsic::isunordered:
	case Intrinsic::ctpop:
	case Intrinsic::ctlz:
	case Intrinsic::cttz:
	case Intrinsic::sqrt:
	return true; // These intrinsics have no side effects.
	}
	return false;
	}

	// 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 llvm::dceInstruction(BasicBlock::iterator &BBI) {
	// Look for un"used" definitions...
	if (isInstructionTriviallyDead(BBI)) {
	BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye
	return true;
	}
	return false;
	}