llvm-project/llvm/lib/CodeGen/InstrSelection/InstrSelection.cpp

381 lines
13 KiB
C++

//===- InstrSelection.cpp - Machine Independant Inst Selection Driver -----===//
//
// Machine-independent driver file for instruction selection. This file
// constructs a forest of BURG instruction trees and then uses the
// BURG-generated tree grammar (BURM) to find the optimal instruction sequences
// for a given machine.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/InstrSelection.h"
#include "llvm/CodeGen/InstrSelectionSupport.h"
#include "llvm/CodeGen/InstrForest.h"
#include "llvm/CodeGen/MachineCodeForInstruction.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/Target/TargetRegInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Function.h"
#include "llvm/iPHINode.h"
#include "llvm/Pass.h"
#include "Support/CommandLine.h"
#include "Support/LeakDetector.h"
using std::vector;
std::vector<MachineInstr*>
FixConstantOperandsForInstr(Instruction* vmInstr, MachineInstr* minstr,
TargetMachine& target);
namespace {
//===--------------------------------------------------------------------===//
// SelectDebugLevel - Allow command line control over debugging.
//
enum SelectDebugLevel_t {
Select_NoDebugInfo,
Select_PrintMachineCode,
Select_DebugInstTrees,
Select_DebugBurgTrees,
};
// Enable Debug Options to be specified on the command line
cl::opt<SelectDebugLevel_t>
SelectDebugLevel("dselect", cl::Hidden,
cl::desc("enable instruction selection debug information"),
cl::values(
clEnumValN(Select_NoDebugInfo, "n", "disable debug output"),
clEnumValN(Select_PrintMachineCode, "y", "print generated machine code"),
clEnumValN(Select_DebugInstTrees, "i",
"print debugging info for instruction selection"),
clEnumValN(Select_DebugBurgTrees, "b", "print burg trees"),
0));
//===--------------------------------------------------------------------===//
// InstructionSelection Pass
//
// This is the actual pass object that drives the instruction selection
// process.
//
class InstructionSelection : public FunctionPass {
TargetMachine &Target;
void InsertCodeForPhis(Function &F);
void InsertPhiElimInstructions(BasicBlock *BB,
const vector<MachineInstr*>& CpVec);
void SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt);
void PostprocessMachineCodeForTree(InstructionNode* instrNode,
int ruleForNode, short* nts);
public:
InstructionSelection(TargetMachine &T) : Target(T) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
bool runOnFunction(Function &F);
};
}
// Register the pass...
static RegisterLLC<InstructionSelection>
X("instselect", "Instruction Selection", createInstructionSelectionPass);
TmpInstruction::TmpInstruction(Value *s1, Value *s2, const std::string &name)
: Instruction(s1->getType(), Instruction::UserOp1, name) {
Operands.push_back(Use(s1, this)); // s1 must be nonnull
if (s2) {
Operands.push_back(Use(s2, this));
}
// TmpInstructions should not be garbage checked.
LeakDetector::removeGarbageObject(this);
}
// Constructor that requires the type of the temporary to be specified.
// Both S1 and S2 may be NULL.(
TmpInstruction::TmpInstruction(const Type *Ty, Value *s1, Value* s2,
const std::string &name)
: Instruction(Ty, Instruction::UserOp1, name) {
if (s1) { Operands.push_back(Use(s1, this)); }
if (s2) { Operands.push_back(Use(s2, this)); }
// TmpInstructions should not be garbage checked.
LeakDetector::removeGarbageObject(this);
}
bool InstructionSelection::runOnFunction(Function &F)
{
//
// Build the instruction trees to be given as inputs to BURG.
//
InstrForest instrForest(&F);
if (SelectDebugLevel >= Select_DebugInstTrees)
{
std::cerr << "\n\n*** Input to instruction selection for function "
<< F.getName() << "\n\n" << F
<< "\n\n*** Instruction trees for function "
<< F.getName() << "\n\n";
instrForest.dump();
}
//
// Invoke BURG instruction selection for each tree
//
for (InstrForest::const_root_iterator RI = instrForest.roots_begin();
RI != instrForest.roots_end(); ++RI)
{
InstructionNode* basicNode = *RI;
assert(basicNode->parent() == NULL && "A `root' node has a parent?");
// Invoke BURM to label each tree node with a state
burm_label(basicNode);
if (SelectDebugLevel >= Select_DebugBurgTrees)
{
printcover(basicNode, 1, 0);
std::cerr << "\nCover cost == " << treecost(basicNode, 1, 0) <<"\n\n";
printMatches(basicNode);
}
// Then recursively walk the tree to select instructions
SelectInstructionsForTree(basicNode, /*goalnt*/1);
}
//
// Create the MachineBasicBlock records and add all of the MachineInstrs
// defined in the MachineCodeForInstruction objects to also live in the
// MachineBasicBlock objects.
//
MachineFunction &MF = MachineFunction::get(&F);
for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
MachineBasicBlock *MCBB = new MachineBasicBlock(BI);
MF.getBasicBlockList().push_back(MCBB);
for (BasicBlock::iterator II = BI->begin(); II != BI->end(); ++II) {
MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(II);
MCBB->insert(MCBB->end(), mvec.begin(), mvec.end());
}
}
// Insert phi elimination code
InsertCodeForPhis(F);
if (SelectDebugLevel >= Select_PrintMachineCode)
{
std::cerr << "\n*** Machine instructions after INSTRUCTION SELECTION\n";
MachineFunction::get(&F).dump();
}
return true;
}
//-------------------------------------------------------------------------
// This method inserts phi elimination code for all BBs in a method
//-------------------------------------------------------------------------
void
InstructionSelection::InsertCodeForPhis(Function &F)
{
// for all basic blocks in function
//
MachineFunction &MF = MachineFunction::get(&F);
for (MachineFunction::iterator BB = MF.begin(); BB != MF.end(); ++BB) {
for (BasicBlock::iterator IIt = BB->getBasicBlock()->begin();
PHINode *PN = dyn_cast<PHINode>(&*IIt); ++IIt) {
// FIXME: This is probably wrong...
Value *PhiCpRes = new PHINode(PN->getType(), "PhiCp:");
// The leak detector shouldn't track these nodes. They are not garbage,
// even though their parent field is never filled in.
//
LeakDetector::removeGarbageObject(PhiCpRes);
// for each incoming value of the phi, insert phi elimination
//
for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i) {
// insert the copy instruction to the predecessor BB
vector<MachineInstr*> mvec, CpVec;
Target.getRegInfo().cpValue2Value(PN->getIncomingValue(i), PhiCpRes,
mvec);
for (vector<MachineInstr*>::iterator MI=mvec.begin();
MI != mvec.end(); ++MI) {
vector<MachineInstr*> CpVec2 =
FixConstantOperandsForInstr(PN, *MI, Target);
CpVec2.push_back(*MI);
CpVec.insert(CpVec.end(), CpVec2.begin(), CpVec2.end());
}
InsertPhiElimInstructions(PN->getIncomingBlock(i), CpVec);
}
vector<MachineInstr*> mvec;
Target.getRegInfo().cpValue2Value(PhiCpRes, PN, mvec);
BB->insert(BB->begin(), mvec.begin(), mvec.end());
} // for each Phi Instr in BB
} // for all BBs in function
}
//-------------------------------------------------------------------------
// Thid method inserts a copy instruction to a predecessor BB as a result
// of phi elimination.
//-------------------------------------------------------------------------
void
InstructionSelection::InsertPhiElimInstructions(BasicBlock *BB,
const vector<MachineInstr*>& CpVec)
{
Instruction *TermInst = (Instruction*)BB->getTerminator();
MachineCodeForInstruction &MC4Term = MachineCodeForInstruction::get(TermInst);
MachineInstr *FirstMIOfTerm = MC4Term.front();
assert (FirstMIOfTerm && "No Machine Instrs for terminator");
MachineFunction &MF = MachineFunction::get(BB->getParent());
// FIXME: if PHI instructions existed in the machine code, this would be
// unnecesary.
MachineBasicBlock *MBB = 0;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
if (I->getBasicBlock() == BB) {
MBB = I;
break;
}
// find the position of first machine instruction generated by the
// terminator of this BB
MachineBasicBlock::iterator MCIt =
std::find(MBB->begin(), MBB->end(), FirstMIOfTerm);
assert(MCIt != MBB->end() && "Start inst of terminator not found");
// insert the copy instructions just before the first machine instruction
// generated for the terminator
MBB->insert(MCIt, CpVec.begin(), CpVec.end());
}
//---------------------------------------------------------------------------
// Function SelectInstructionsForTree
//
// Recursively walk the tree to select instructions.
// Do this top-down so that child instructions can exploit decisions
// made at the child instructions.
//
// E.g., if br(setle(reg,const)) decides the constant is 0 and uses
// a branch-on-integer-register instruction, then the setle node
// can use that information to avoid generating the SUBcc instruction.
//
// Note that this cannot be done bottom-up because setle must do this
// only if it is a child of the branch (otherwise, the result of setle
// may be used by multiple instructions).
//---------------------------------------------------------------------------
void
InstructionSelection::SelectInstructionsForTree(InstrTreeNode* treeRoot,
int goalnt)
{
// Get the rule that matches this node.
//
int ruleForNode = burm_rule(treeRoot->state, goalnt);
if (ruleForNode == 0) {
std::cerr << "Could not match instruction tree for instr selection\n";
abort();
}
// Get this rule's non-terminals and the corresponding child nodes (if any)
//
short *nts = burm_nts[ruleForNode];
// First, select instructions for the current node and rule.
// (If this is a list node, not an instruction, then skip this step).
// This function is specific to the target architecture.
//
if (treeRoot->opLabel != VRegListOp)
{
vector<MachineInstr*> minstrVec;
InstructionNode* instrNode = (InstructionNode*)treeRoot;
assert(instrNode->getNodeType() == InstrTreeNode::NTInstructionNode);
GetInstructionsByRule(instrNode, ruleForNode, nts, Target, minstrVec);
MachineCodeForInstruction &mvec =
MachineCodeForInstruction::get(instrNode->getInstruction());
mvec.insert(mvec.end(), minstrVec.begin(), minstrVec.end());
}
// Then, recursively compile the child nodes, if any.
//
if (nts[0])
{ // i.e., there is at least one kid
InstrTreeNode* kids[2];
int currentRule = ruleForNode;
burm_kids(treeRoot, currentRule, kids);
// First skip over any chain rules so that we don't visit
// the current node again.
//
while (ThisIsAChainRule(currentRule))
{
currentRule = burm_rule(treeRoot->state, nts[0]);
nts = burm_nts[currentRule];
burm_kids(treeRoot, currentRule, kids);
}
// Now we have the first non-chain rule so we have found
// the actual child nodes. Recursively compile them.
//
for (unsigned i = 0; nts[i]; i++)
{
assert(i < 2);
InstrTreeNode::InstrTreeNodeType nodeType = kids[i]->getNodeType();
if (nodeType == InstrTreeNode::NTVRegListNode ||
nodeType == InstrTreeNode::NTInstructionNode)
SelectInstructionsForTree(kids[i], nts[i]);
}
}
// Finally, do any postprocessing on this node after its children
// have been translated
//
if (treeRoot->opLabel != VRegListOp)
PostprocessMachineCodeForTree((InstructionNode*)treeRoot, ruleForNode, nts);
}
//---------------------------------------------------------------------------
// Function PostprocessMachineCodeForTree
//
// Apply any final cleanups to machine code for the root of a subtree
// after selection for all its children has been completed.
//
void
InstructionSelection::PostprocessMachineCodeForTree(InstructionNode* instrNode,
int ruleForNode,
short* nts)
{
// Fix up any constant operands in the machine instructions to either
// use an immediate field or to load the constant into a register
// Walk backwards and use direct indexes to allow insertion before current
//
Instruction* vmInstr = instrNode->getInstruction();
MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(vmInstr);
for (unsigned i = mvec.size(); i != 0; --i)
{
vector<MachineInstr*> loadConstVec =
FixConstantOperandsForInstr(vmInstr, mvec[i-1], Target);
mvec.insert(mvec.begin()+i-1, loadConstVec.begin(), loadConstVec.end());
}
}
//===----------------------------------------------------------------------===//
// createInstructionSelectionPass - Public entrypoint for instruction selection
// and this file as a whole...
//
Pass *createInstructionSelectionPass(TargetMachine &T) {
return new InstructionSelection(T);
}