lib/Transforms/IPO/IPConstantPropagation.cpp - platform/external/llvm - Gitiles

 //===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This pass implements an _extremely_ simple interprocedural constant
 // propagation pass.  It could certainly be improved in many different ways,
 // like using a worklist.  This pass makes arguments dead, but does not remove
 // them.  The existing dead argument elimination pass should be run after this
 // to clean up the mess.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "ipconstprop"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Constants.h"
 #include "llvm/Instructions.h"
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/SmallVector.h"
 using namespace llvm;

 STATISTIC(NumArgumentsProped, "Number of args turned into constants");
 STATISTIC(NumReturnValProped, "Number of return values turned into constants");

 namespace {
   /// IPCP - The interprocedural constant propagation pass
   ///
   struct VISIBILITY_HIDDEN IPCP : public ModulePass {
     static char ID; // Pass identification, replacement for typeid
     IPCP() : ModulePass((intptr_t)&ID) {}

     bool runOnModule(Module &M);
   private:
     bool PropagateConstantsIntoArguments(Function &F);
     bool PropagateConstantReturn(Function &F);
   };
 }

 char IPCP::ID = 0;
 static RegisterPass<IPCP>
 X("ipconstprop", "Interprocedural constant propagation");

 ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }

 bool IPCP::runOnModule(Module &M) {
   bool Changed = false;
   bool LocalChange = true;

   // FIXME: instead of using smart algorithms, we just iterate until we stop
   // making changes.
   while (LocalChange) {
     LocalChange = false;
     for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
       if (!I->isDeclaration()) {
         // Delete any klingons.
         I->removeDeadConstantUsers();
         if (I->hasInternalLinkage())
           LocalChange |= PropagateConstantsIntoArguments(*I);
         Changed |= PropagateConstantReturn(*I);
       }
     Changed |= LocalChange;
   }
   return Changed;
 }

 /// PropagateConstantsIntoArguments - Look at all uses of the specified
 /// function.  If all uses are direct call sites, and all pass a particular
 /// constant in for an argument, propagate that constant in as the argument.
 ///
 bool IPCP::PropagateConstantsIntoArguments(Function &F) {
   if (F.arg_empty() || F.use_empty()) return false; // No arguments? Early exit.

   // For each argument, keep track of its constant value and whether it is a
   // constant or not.  The bool is driven to true when found to be non-constant.
   SmallVector<std::pair<Constant*, bool>, 16> ArgumentConstants;
   ArgumentConstants.resize(F.arg_size());

   unsigned NumNonconstant = 0;
   for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
     // Used by a non-instruction, or not the callee of a function, do not
     // transform.
     if (UI.getOperandNo() != 0 ||
         (!isa<CallInst>(*UI) && !isa<InvokeInst>(*UI)))
       return false;

     CallSite CS = CallSite::get(cast<Instruction>(*UI));

     // Check out all of the potentially constant arguments.  Note that we don't
     // inspect varargs here.
     CallSite::arg_iterator AI = CS.arg_begin();
     Function::arg_iterator Arg = F.arg_begin();
     for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
          ++i, ++AI, ++Arg) {

       // If this argument is known non-constant, ignore it.
       if (ArgumentConstants[i].second)
         continue;

       Constant *C = dyn_cast<Constant>(*AI);
       if (C && ArgumentConstants[i].first == 0) {
         ArgumentConstants[i].first = C;   // First constant seen.
       } else if (C && ArgumentConstants[i].first == C) {
         // Still the constant value we think it is.
       } else if (*AI == &*Arg) {
         // Ignore recursive calls passing argument down.
       } else {
         // Argument became non-constant.  If all arguments are non-constant now,
         // give up on this function.
         if (++NumNonconstant == ArgumentConstants.size())
           return false;
         ArgumentConstants[i].second = true;
       }
     }
   }

   // If we got to this point, there is a constant argument!
   assert(NumNonconstant != ArgumentConstants.size());
   bool MadeChange = false;
   Function::arg_iterator AI = F.arg_begin();
   for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
     // Do we have a constant argument?
     if (ArgumentConstants[i].second || AI->use_empty())
       continue;

     Value *V = ArgumentConstants[i].first;
     if (V == 0) V = UndefValue::get(AI->getType());
     AI->replaceAllUsesWith(V);
     ++NumArgumentsProped;
     MadeChange = true;
   }
   return MadeChange;
 }


 // Check to see if this function returns a constant.  If so, replace all callers
 // that user the return value with the returned valued.  If we can replace ALL
 // callers,
 bool IPCP::PropagateConstantReturn(Function &F) {
   if (F.getReturnType() == Type::VoidTy)
     return false; // No return value.

   // If this function could be overridden later in the link stage, we can't
   // propagate information about its results into callers.
   if (F.hasLinkOnceLinkage() || F.hasWeakLinkage())
     return false;

   // Check to see if this function returns a constant.
   SmallVector<Value *,4> RetVals;
   const StructType *STy = dyn_cast<StructType>(F.getReturnType());
   if (STy)
     RetVals.assign(STy->getNumElements(), 0);
   else
     RetVals.push_back(0);

   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
     if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
       assert(RetVals.size() == RI->getNumOperands() &&
              "Invalid ReturnInst operands!");
       for (unsigned i = 0, e = RetVals.size(); i != e; ++i) {
         if (isa<UndefValue>(RI->getOperand(i)))
           continue; // Ignore
         Constant *C = dyn_cast<Constant>(RI->getOperand(i));
         if (C == 0)
           return false; // Does not return a constant.

         Value *RV = RetVals[i];
         if (RV == 0)
           RetVals[i] = C;
         else if (RV != C)
           return false; // Does not return the same constant.
       }
     }

   if (STy) {
     for (unsigned i = 0, e = RetVals.size(); i < e; ++i)
       if (RetVals[i] == 0)
         RetVals[i] = UndefValue::get(STy->getElementType(i));
   } else {
     assert(RetVals.size() == 1);
     if (RetVals[0] == 0)
       RetVals[0] = UndefValue::get(F.getReturnType());
   }

   // If we got here, the function returns a constant value.  Loop over all
   // users, replacing any uses of the return value with the returned constant.
   bool ReplacedAllUsers = true;
   bool MadeChange = false;
   for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
     // Make sure this is an invoke or call and that the use is for the callee.
     if (!(isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) ||
         UI.getOperandNo() != 0) {
       ReplacedAllUsers = false;
       continue;
     }

     Instruction *Call = cast<Instruction>(*UI);
     if (Call->use_empty())
       continue;

     MadeChange = true;

     if (STy == 0) {
       Call->replaceAllUsesWith(RetVals[0]);
       continue;
     }

     while (!Call->use_empty()) {
       GetResultInst *GR = cast<GetResultInst>(Call->use_back());
       GR->replaceAllUsesWith(RetVals[GR->getIndex()]);
       GR->eraseFromParent();
     }
   }

   // If we replace all users with the returned constant, and there can be no
   // other callers of the function, replace the constant being returned in the
   // function with an undef value.
   if (ReplacedAllUsers && F.hasInternalLinkage()) {
     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
       if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
         for (unsigned i = 0, e = RetVals.size(); i < e; ++i) {
           Value *RetVal = RetVals[i];
           if (isa<UndefValue>(RetVal))
             continue;
           Value *RV = UndefValue::get(RetVal->getType());
           if (RI->getOperand(i) != RV) {
             RI->setOperand(i, RV);
             MadeChange = true;
           }
         }
       }
     }
   }

   if (MadeChange) ++NumReturnValProped;
   return MadeChange;
 }
	//===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This pass implements an _extremely_ simple interprocedural constant
	// propagation pass. It could certainly be improved in many different ways,
	// like using a worklist. This pass makes arguments dead, but does not remove
	// them. The existing dead argument elimination pass should be run after this
	// to clean up the mess.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "ipconstprop"
	#include "llvm/Transforms/IPO.h"
	#include "llvm/Constants.h"
	#include "llvm/Instructions.h"
	#include "llvm/Module.h"
	#include "llvm/Pass.h"
	#include "llvm/Support/CallSite.h"
	#include "llvm/Support/Compiler.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/ADT/SmallVector.h"
	using namespace llvm;

	STATISTIC(NumArgumentsProped, "Number of args turned into constants");
	STATISTIC(NumReturnValProped, "Number of return values turned into constants");

	namespace {
	/// IPCP - The interprocedural constant propagation pass
	///
	struct VISIBILITY_HIDDEN IPCP : public ModulePass {
	static char ID; // Pass identification, replacement for typeid
	IPCP() : ModulePass((intptr_t)&ID) {}

	bool runOnModule(Module &M);
	private:
	bool PropagateConstantsIntoArguments(Function &F);
	bool PropagateConstantReturn(Function &F);
	};
	}

	char IPCP::ID = 0;
	static RegisterPass<IPCP>
	X("ipconstprop", "Interprocedural constant propagation");

	ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }

	bool IPCP::runOnModule(Module &M) {
	bool Changed = false;
	bool LocalChange = true;

	// FIXME: instead of using smart algorithms, we just iterate until we stop
	// making changes.
	while (LocalChange) {
	LocalChange = false;
	for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
	if (!I->isDeclaration()) {
	// Delete any klingons.
	I->removeDeadConstantUsers();
	if (I->hasInternalLinkage())
	LocalChange \|= PropagateConstantsIntoArguments(*I);
	Changed \|= PropagateConstantReturn(*I);
	}
	Changed \|= LocalChange;
	}
	return Changed;
	}

	/// PropagateConstantsIntoArguments - Look at all uses of the specified
	/// function. If all uses are direct call sites, and all pass a particular
	/// constant in for an argument, propagate that constant in as the argument.
	///
	bool IPCP::PropagateConstantsIntoArguments(Function &F) {
	if (F.arg_empty() \|\| F.use_empty()) return false; // No arguments? Early exit.

	// For each argument, keep track of its constant value and whether it is a
	// constant or not. The bool is driven to true when found to be non-constant.
	SmallVector<std::pair<Constant*, bool>, 16> ArgumentConstants;
	ArgumentConstants.resize(F.arg_size());

	unsigned NumNonconstant = 0;
	for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
	// Used by a non-instruction, or not the callee of a function, do not
	// transform.
	if (UI.getOperandNo() != 0 \|\|
	(!isa<CallInst>(UI) && !isa<InvokeInst>(UI)))
	return false;

	CallSite CS = CallSite::get(cast<Instruction>(*UI));

	// Check out all of the potentially constant arguments. Note that we don't
	// inspect varargs here.
	CallSite::arg_iterator AI = CS.arg_begin();
	Function::arg_iterator Arg = F.arg_begin();
	for (unsigned i = 0, e = ArgumentConstants.size(); i != e;
	++i, ++AI, ++Arg) {

	// If this argument is known non-constant, ignore it.
	if (ArgumentConstants[i].second)
	continue;

	Constant C = dyn_cast<Constant>(AI);
	if (C && ArgumentConstants[i].first == 0) {
	ArgumentConstants[i].first = C; // First constant seen.
	} else if (C && ArgumentConstants[i].first == C) {
	// Still the constant value we think it is.
	} else if (AI == &Arg) {
	// Ignore recursive calls passing argument down.
	} else {
	// Argument became non-constant. If all arguments are non-constant now,
	// give up on this function.
	if (++NumNonconstant == ArgumentConstants.size())
	return false;
	ArgumentConstants[i].second = true;
	}
	}
	}

	// If we got to this point, there is a constant argument!
	assert(NumNonconstant != ArgumentConstants.size());
	bool MadeChange = false;
	Function::arg_iterator AI = F.arg_begin();
	for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
	// Do we have a constant argument?
	if (ArgumentConstants[i].second \|\| AI->use_empty())
	continue;

	Value *V = ArgumentConstants[i].first;
	if (V == 0) V = UndefValue::get(AI->getType());
	AI->replaceAllUsesWith(V);
	++NumArgumentsProped;
	MadeChange = true;
	}
	return MadeChange;
	}


	// Check to see if this function returns a constant. If so, replace all callers
	// that user the return value with the returned valued. If we can replace ALL
	// callers,
	bool IPCP::PropagateConstantReturn(Function &F) {
	if (F.getReturnType() == Type::VoidTy)
	return false; // No return value.

	// If this function could be overridden later in the link stage, we can't
	// propagate information about its results into callers.
	if (F.hasLinkOnceLinkage() \|\| F.hasWeakLinkage())
	return false;

	// Check to see if this function returns a constant.
	SmallVector<Value *,4> RetVals;
	const StructType *STy = dyn_cast<StructType>(F.getReturnType());
	if (STy)
	RetVals.assign(STy->getNumElements(), 0);
	else
	RetVals.push_back(0);

	for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
	if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
	assert(RetVals.size() == RI->getNumOperands() &&
	"Invalid ReturnInst operands!");
	for (unsigned i = 0, e = RetVals.size(); i != e; ++i) {
	if (isa<UndefValue>(RI->getOperand(i)))
	continue; // Ignore
	Constant *C = dyn_cast<Constant>(RI->getOperand(i));
	if (C == 0)
	return false; // Does not return a constant.

	Value *RV = RetVals[i];
	if (RV == 0)
	RetVals[i] = C;
	else if (RV != C)
	return false; // Does not return the same constant.
	}
	}

	if (STy) {
	for (unsigned i = 0, e = RetVals.size(); i < e; ++i)
	if (RetVals[i] == 0)
	RetVals[i] = UndefValue::get(STy->getElementType(i));
	} else {
	assert(RetVals.size() == 1);
	if (RetVals[0] == 0)
	RetVals[0] = UndefValue::get(F.getReturnType());
	}

	// If we got here, the function returns a constant value. Loop over all
	// users, replacing any uses of the return value with the returned constant.
	bool ReplacedAllUsers = true;
	bool MadeChange = false;
	for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
	// Make sure this is an invoke or call and that the use is for the callee.
	if (!(isa<InvokeInst>(UI) \|\| isa<CallInst>(UI)) \|\|
	UI.getOperandNo() != 0) {
	ReplacedAllUsers = false;
	continue;
	}

	Instruction Call = cast<Instruction>(UI);
	if (Call->use_empty())
	continue;

	MadeChange = true;

	if (STy == 0) {
	Call->replaceAllUsesWith(RetVals[0]);
	continue;
	}

	while (!Call->use_empty()) {
	GetResultInst *GR = cast<GetResultInst>(Call->use_back());
	GR->replaceAllUsesWith(RetVals[GR->getIndex()]);
	GR->eraseFromParent();
	}
	}

	// If we replace all users with the returned constant, and there can be no
	// other callers of the function, replace the constant being returned in the
	// function with an undef value.
	if (ReplacedAllUsers && F.hasInternalLinkage()) {
	for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
	if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
	for (unsigned i = 0, e = RetVals.size(); i < e; ++i) {
	Value *RetVal = RetVals[i];
	if (isa<UndefValue>(RetVal))
	continue;
	Value *RV = UndefValue::get(RetVal->getType());
	if (RI->getOperand(i) != RV) {
	RI->setOperand(i, RV);
	MadeChange = true;
	}
	}
	}
	}
	}

	if (MadeChange) ++NumReturnValProped;
	return MadeChange;
	}