forked from OSchip/llvm-project
353 lines
13 KiB
C++
353 lines
13 KiB
C++
//===-- 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;
|
|
}
|
|
|
|
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)) {
|
|
if (Constant *Op0 = dyn_cast<Constant>(I->getOperand(0)))
|
|
if (Constant *Op1 = dyn_cast<Constant>(I->getOperand(1)))
|
|
return ConstantExpr::get(I->getOpcode(), Op0, Op1);
|
|
return 0; // Operands not constants.
|
|
}
|
|
|
|
// Scan the operand list, checking to see if the are all constants, if so,
|
|
// hand off to ConstantFoldInstOperands.
|
|
std::vector<Constant*> Ops;
|
|
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
|
|
if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
|
|
Ops.push_back(Op);
|
|
else
|
|
return 0; // All operands not constant!
|
|
|
|
return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops);
|
|
}
|
|
|
|
/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
|
|
/// specified opcode and operands. If successful, the constant result is
|
|
/// returned, if not, null is returned. Note that this function can fail when
|
|
/// attempting to fold instructions like loads and stores, which have no
|
|
/// constant expression form.
|
|
///
|
|
Constant *llvm::ConstantFoldInstOperands(unsigned Opc, const Type *DestTy,
|
|
const std::vector<Constant*> &Ops) {
|
|
if (Opc >= Instruction::BinaryOpsBegin && Opc < Instruction::BinaryOpsEnd)
|
|
return ConstantExpr::get(Opc, Ops[0], Ops[1]);
|
|
|
|
switch (Opc) {
|
|
default: return 0;
|
|
case Instruction::Call:
|
|
if (Function *F = dyn_cast<Function>(Ops[0])) {
|
|
if (canConstantFoldCallTo(F)) {
|
|
std::vector<Constant*> Args(Ops.begin()+1, Ops.end());
|
|
return ConstantFoldCall(F, Args);
|
|
}
|
|
}
|
|
return 0;
|
|
case Instruction::Shl:
|
|
case Instruction::Shr:
|
|
return ConstantExpr::get(Opc, Ops[0], Ops[1]);
|
|
case Instruction::Cast:
|
|
return ConstantExpr::getCast(Ops[0], DestTy);
|
|
case Instruction::Select:
|
|
return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
|
|
case Instruction::ExtractElement:
|
|
return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
|
|
case Instruction::InsertElement:
|
|
return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
|
|
case Instruction::ShuffleVector:
|
|
return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
|
|
case Instruction::GetElementPtr:
|
|
return ConstantExpr::getGetElementPtr(Ops[0],
|
|
std::vector<Constant*>(Ops.begin()+1,
|
|
Ops.end()));
|
|
}
|
|
}
|
|
|
|
// 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)) {
|
|
ConstantInt *CU = cast<ConstantInt>(I.getOperand());
|
|
assert(CU->getZExtValue() < STy->getNumElements() &&
|
|
"Struct index out of range!");
|
|
unsigned El = (unsigned)CU->getZExtValue();
|
|
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())) {
|
|
if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
|
|
if (CI->getZExtValue() >= ATy->getNumElements())
|
|
return 0;
|
|
if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
|
|
C = CA->getOperand(CI->getZExtValue());
|
|
else if (isa<ConstantAggregateZero>(C))
|
|
C = Constant::getNullValue(ATy->getElementType());
|
|
else if (isa<UndefValue>(C))
|
|
C = UndefValue::get(ATy->getElementType());
|
|
else
|
|
return 0;
|
|
} else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
|
|
if (CI->getZExtValue() >= PTy->getNumElements())
|
|
return 0;
|
|
if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
|
|
C = CP->getOperand(CI->getZExtValue());
|
|
else if (isa<ConstantAggregateZero>(C))
|
|
C = Constant::getNullValue(PTy->getElementType());
|
|
else if (isa<UndefValue>(C))
|
|
C = UndefValue::get(PTy->getElementType());
|
|
else
|
|
return 0;
|
|
} 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()) {
|
|
unsigned IntrinsicID = F->getIntrinsicID();
|
|
#define GET_SIDE_EFFECT_INFO
|
|
#include "llvm/Intrinsics.gen"
|
|
#undef GET_SIDE_EFFECT_INFO
|
|
}
|
|
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;
|
|
}
|