llvm-6502/lib/Transforms/Utils/LowerSwitch.cpp

306 lines
11 KiB
C++
Raw Normal View History

//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The LowerSwitch transformation rewrites switch instructions with a sequence
// of branches, which allows targets to get away with not implementing the
// switch instruction until it is convenient.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
namespace {
/// LowerSwitch Pass - Replace all SwitchInst instructions with chained branch
/// instructions.
class LowerSwitch : public FunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
LowerSwitch() : FunctionPass(ID) {
initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// This is a cluster of orthogonal Transforms
AU.addPreserved<UnifyFunctionExitNodes>();
AU.addPreserved("mem2reg");
AU.addPreservedID(LowerInvokePassID);
}
struct CaseRange {
Constant* Low;
Constant* High;
BasicBlock* BB;
CaseRange(Constant *low = 0, Constant *high = 0, BasicBlock *bb = 0) :
Low(low), High(high), BB(bb) { }
};
typedef std::vector<CaseRange> CaseVector;
typedef std::vector<CaseRange>::iterator CaseItr;
private:
void processSwitchInst(SwitchInst *SI);
BasicBlock* switchConvert(CaseItr Begin, CaseItr End, Value* Val,
BasicBlock* OrigBlock, BasicBlock* Default);
BasicBlock* newLeafBlock(CaseRange& Leaf, Value* Val,
BasicBlock* OrigBlock, BasicBlock* Default);
unsigned Clusterify(CaseVector& Cases, SwitchInst *SI);
};
}
char LowerSwitch::ID = 0;
INITIALIZE_PASS(LowerSwitch, "lowerswitch",
"Lower SwitchInst's to branches", false, false)
// Publicly exposed interface to pass...
char &llvm::LowerSwitchID = LowerSwitch::ID;
// createLowerSwitchPass - Interface to this file...
FunctionPass *llvm::createLowerSwitchPass() {
return new LowerSwitch();
}
bool LowerSwitch::runOnFunction(Function &F) {
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
BasicBlock *Cur = I++; // Advance over block so we don't traverse new blocks
if (SwitchInst *SI = dyn_cast<SwitchInst>(Cur->getTerminator())) {
Changed = true;
processSwitchInst(SI);
}
}
return Changed;
}
// operator<< - Used for debugging purposes.
//
static raw_ostream& operator<<(raw_ostream &O,
const LowerSwitch::CaseVector &C)
LLVM_ATTRIBUTE_USED;
static raw_ostream& operator<<(raw_ostream &O,
const LowerSwitch::CaseVector &C) {
O << "[";
for (LowerSwitch::CaseVector::const_iterator B = C.begin(),
E = C.end(); B != E; ) {
O << *B->Low << " -" << *B->High;
if (++B != E) O << ", ";
}
return O << "]";
}
// switchConvert - Convert the switch statement into a binary lookup of
// the case values. The function recursively builds this tree.
//
BasicBlock* LowerSwitch::switchConvert(CaseItr Begin, CaseItr End,
Value* Val, BasicBlock* OrigBlock,
BasicBlock* Default)
{
unsigned Size = End - Begin;
if (Size == 1)
return newLeafBlock(*Begin, Val, OrigBlock, Default);
unsigned Mid = Size / 2;
std::vector<CaseRange> LHS(Begin, Begin + Mid);
DEBUG(dbgs() << "LHS: " << LHS << "\n");
std::vector<CaseRange> RHS(Begin + Mid, End);
DEBUG(dbgs() << "RHS: " << RHS << "\n");
CaseRange& Pivot = *(Begin + Mid);
DEBUG(dbgs() << "Pivot ==> "
<< cast<ConstantInt>(Pivot.Low)->getValue() << " -"
<< cast<ConstantInt>(Pivot.High)->getValue() << "\n");
BasicBlock* LBranch = switchConvert(LHS.begin(), LHS.end(), Val,
OrigBlock, Default);
BasicBlock* RBranch = switchConvert(RHS.begin(), RHS.end(), Val,
OrigBlock, Default);
// Create a new node that checks if the value is < pivot. Go to the
// left branch if it is and right branch if not.
Function* F = OrigBlock->getParent();
BasicBlock* NewNode = BasicBlock::Create(Val->getContext(), "NodeBlock");
Function::iterator FI = OrigBlock;
F->getBasicBlockList().insert(++FI, NewNode);
ICmpInst* Comp = new ICmpInst(ICmpInst::ICMP_ULT,
Val, Pivot.Low, "Pivot");
NewNode->getInstList().push_back(Comp);
BranchInst::Create(LBranch, RBranch, Comp, NewNode);
return NewNode;
}
// newLeafBlock - Create a new leaf block for the binary lookup tree. It
// checks if the switch's value == the case's value. If not, then it
// jumps to the default branch. At this point in the tree, the value
// can't be another valid case value, so the jump to the "default" branch
// is warranted.
//
BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
BasicBlock* OrigBlock,
BasicBlock* Default)
{
Function* F = OrigBlock->getParent();
BasicBlock* NewLeaf = BasicBlock::Create(Val->getContext(), "LeafBlock");
Function::iterator FI = OrigBlock;
F->getBasicBlockList().insert(++FI, NewLeaf);
// Emit comparison
ICmpInst* Comp = NULL;
if (Leaf.Low == Leaf.High) {
// Make the seteq instruction...
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_EQ, Val,
Leaf.Low, "SwitchLeaf");
} else {
// Make range comparison
if (cast<ConstantInt>(Leaf.Low)->isMinValue(true /*isSigned*/)) {
// Val >= Min && Val <= Hi --> Val <= Hi
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
"SwitchLeaf");
} else if (cast<ConstantInt>(Leaf.Low)->isZero()) {
// Val >= 0 && Val <= Hi --> Val <=u Hi
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
"SwitchLeaf");
} else {
// Emit V-Lo <=u Hi-Lo
Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
Instruction* Add = BinaryOperator::CreateAdd(Val, NegLo,
Val->getName()+".off",
NewLeaf);
Constant *UpperBound = ConstantExpr::getAdd(NegLo, Leaf.High);
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
"SwitchLeaf");
}
}
// Make the conditional branch...
BasicBlock* Succ = Leaf.BB;
BranchInst::Create(Succ, Default, Comp, NewLeaf);
// If there were any PHI nodes in this successor, rewrite one entry
// from OrigBlock to come from NewLeaf.
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
PHINode* PN = cast<PHINode>(I);
// Remove all but one incoming entries from the cluster
uint64_t Range = cast<ConstantInt>(Leaf.High)->getSExtValue() -
cast<ConstantInt>(Leaf.Low)->getSExtValue();
for (uint64_t j = 0; j < Range; ++j) {
PN->removeIncomingValue(OrigBlock);
}
int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
}
return NewLeaf;
}
// Clusterify - Transform simple list of Cases into list of CaseRange's
unsigned LowerSwitch::Clusterify(CaseVector& Cases, SwitchInst *SI) {
IntegersSubsetToBB TheClusterifier;
// Start with "simple" cases
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock *SuccBB = i.getCaseSuccessor();
IntegersSubset CaseRanges = i.getCaseValueEx();
TheClusterifier.add(CaseRanges, SuccBB);
}
TheClusterifier.optimize();
size_t numCmps = 0;
for (IntegersSubsetToBB::RangeIterator i = TheClusterifier.begin(),
e = TheClusterifier.end(); i != e; ++i, ++numCmps) {
IntegersSubsetToBB::Cluster &C = *i;
PR1255: Case Ranges Implemented IntItem - the wrapper around APInt. Why not to use APInt item directly right now? 1. It will very difficult to implement case ranges as series of small patches. We got several large and heavy patches. Each patch will about 90-120 kb. If you replace ConstantInt with APInt in SwitchInst you will need to changes at the same time all Readers,Writers and absolutely all passes that uses SwitchInst. 2. We can implement APInt pool inside and save memory space. E.g. we use several switches that works with 256 bit items (switch on signatures, or strings). We can avoid value duplicates in this case. 3. IntItem can be easyly easily replaced with APInt. 4. Currenly we can interpret IntItem both as ConstantInt and as APInt. It allows to provide SwitchInst methods that works with ConstantInt for non-updated passes. Why I need it right now? Currently I need to update SimplifyCFG pass (EqualityComparisons). I need to work with APInts directly a lot, so peaces of code ConstantInt *V = ...; if (V->getValue().ugt(AnotherV->getValue()) { ... } will look awful. Much more better this way: IntItem V = ConstantIntVal->getValue(); if (AnotherV < V) { } Of course any reviews are welcome. P.S.: I'm also going to rename ConstantRangesSet to IntegersSubset, and CRSBuilder to IntegersSubsetMapping (allows to map individual subsets of integers to the BasicBlocks). Since in future these classes will founded on APInt, it will possible to use them in more generic ways. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157576 91177308-0d34-0410-b5e6-96231b3b80d8
2012-05-28 12:39:09 +00:00
// FIXME: Currently work with ConstantInt based numbers.
// Changing it to APInt based is a pretty heavy for this commit.
Cases.push_back(CaseRange(C.first.getLow().toConstantInt(),
C.first.getHigh().toConstantInt(), C.second));
if (C.first.isSingleNumber())
// A range counts double, since it requires two compares.
++numCmps;
}
return numCmps;
}
// processSwitchInst - Replace the specified switch instruction with a sequence
// of chained if-then insts in a balanced binary search.
//
void LowerSwitch::processSwitchInst(SwitchInst *SI) {
BasicBlock *CurBlock = SI->getParent();
BasicBlock *OrigBlock = CurBlock;
Function *F = CurBlock->getParent();
Value *Val = SI->getCondition(); // The value we are switching on...
BasicBlock* Default = SI->getDefaultDest();
// If there is only the default destination, don't bother with the code below.
SwitchInst refactoring. The purpose of refactoring is to hide operand roles from SwitchInst user (programmer). If you want to play with operands directly, probably you will need lower level methods than SwitchInst ones (TerminatorInst or may be User). After this patch we can reorganize SwitchInst operands and successors as we want. What was done: 1. Changed semantics of index inside the getCaseValue method: getCaseValue(0) means "get first case", not a condition. Use getCondition() if you want to resolve the condition. I propose don't mix SwitchInst case indexing with low level indexing (TI successors indexing, User's operands indexing), since it may be dangerous. 2. By the same reason findCaseValue(ConstantInt*) returns actual number of case value. 0 means first case, not default. If there is no case with given value, ErrorIndex will returned. 3. Added getCaseSuccessor method. I propose to avoid usage of TerminatorInst::getSuccessor if you want to resolve case successor BB. Use getCaseSuccessor instead, since internal SwitchInst organization of operands/successors is hidden and may be changed in any moment. 4. Added resolveSuccessorIndex and resolveCaseIndex. The main purpose of these methods is to see how case successors are really mapped in TerminatorInst. 4.1 "resolveSuccessorIndex" was created if you need to level down from SwitchInst to TerminatorInst. It returns TerminatorInst's successor index for given case successor. 4.2 "resolveCaseIndex" converts low level successors index to case index that curresponds to the given successor. Note: There are also related compatability fix patches for dragonegg, klee, llvm-gcc-4.0, llvm-gcc-4.2, safecode, clang. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149481 91177308-0d34-0410-b5e6-96231b3b80d8
2012-02-01 07:49:51 +00:00
if (!SI->getNumCases()) {
BranchInst::Create(SI->getDefaultDest(), CurBlock);
CurBlock->getInstList().erase(SI);
return;
}
// Create a new, empty default block so that the new hierarchy of
// if-then statements go to this and the PHI nodes are happy.
BasicBlock* NewDefault = BasicBlock::Create(SI->getContext(), "NewDefault");
F->getBasicBlockList().insert(Default, NewDefault);
BranchInst::Create(Default, NewDefault);
// If there is an entry in any PHI nodes for the default edge, make sure
// to update them as well.
for (BasicBlock::iterator I = Default->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewDefault);
}
// Prepare cases vector.
CaseVector Cases;
unsigned numCmps = Clusterify(Cases, SI);
DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
<< ". Total compares: " << numCmps << "\n");
DEBUG(dbgs() << "Cases: " << Cases << "\n");
(void)numCmps;
BasicBlock* SwitchBlock = switchConvert(Cases.begin(), Cases.end(), Val,
OrigBlock, NewDefault);
// Branch to our shiny new if-then stuff...
BranchInst::Create(SwitchBlock, OrigBlock);
// We are now done with the switch instruction, delete it.
CurBlock->getInstList().erase(SI);
}