1 //===- InstrSelection.cpp - Machine Independant Inst Selection Driver -----===//
3 // Machine-independent driver file for instruction selection. This file
4 // constructs a forest of BURG instruction trees and then uses the
5 // BURG-generated tree grammar (BURM) to find the optimal instruction sequences
6 // for a given machine.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/CodeGen/InstrSelection.h"
11 #include "llvm/CodeGen/InstrSelectionSupport.h"
12 #include "llvm/CodeGen/InstrForest.h"
13 #include "llvm/CodeGen/MachineCodeForInstruction.h"
14 #include "llvm/CodeGen/MachineFunction.h"
15 #include "llvm/Target/MachineRegInfo.h"
16 #include "llvm/Target/TargetMachine.h"
17 #include "llvm/Function.h"
18 #include "llvm/iPHINode.h"
19 #include "llvm/Pass.h"
20 #include "Support/CommandLine.h"
21 #include "Support/LeakDetector.h"
26 //===--------------------------------------------------------------------===//
27 // SelectDebugLevel - Allow command line control over debugging.
29 enum SelectDebugLevel_t {
31 Select_PrintMachineCode,
32 Select_DebugInstTrees,
33 Select_DebugBurgTrees,
36 // Enable Debug Options to be specified on the command line
37 cl::opt<SelectDebugLevel_t>
38 SelectDebugLevel("dselect", cl::Hidden,
39 cl::desc("enable instruction selection debug information"),
41 clEnumValN(Select_NoDebugInfo, "n", "disable debug output"),
42 clEnumValN(Select_PrintMachineCode, "y", "print generated machine code"),
43 clEnumValN(Select_DebugInstTrees, "i",
44 "print debugging info for instruction selection"),
45 clEnumValN(Select_DebugBurgTrees, "b", "print burg trees"),
49 //===--------------------------------------------------------------------===//
50 // InstructionSelection Pass
52 // This is the actual pass object that drives the instruction selection
55 class InstructionSelection : public FunctionPass {
56 TargetMachine &Target;
57 void InsertCodeForPhis(Function &F);
58 void InsertPhiElimInstructions(BasicBlock *BB,
59 const vector<MachineInstr*>& CpVec);
60 void SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt);
61 void PostprocessMachineCodeForTree(InstructionNode* instrNode,
62 int ruleForNode, short* nts);
64 InstructionSelection(TargetMachine &T) : Target(T) {}
66 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
70 bool runOnFunction(Function &F);
74 // Register the pass...
75 static RegisterLLC<InstructionSelection>
76 X("instselect", "Instruction Selection", createInstructionSelectionPass);
78 TmpInstruction::TmpInstruction(Value *s1, Value *s2, const std::string &name)
79 : Instruction(s1->getType(), Instruction::UserOp1, name) {
80 Operands.push_back(Use(s1, this)); // s1 must be nonnull
82 Operands.push_back(Use(s2, this));
85 // TmpInstructions should not be garbage checked.
86 LeakDetector::removeGarbageObject(this);
89 // Constructor that requires the type of the temporary to be specified.
90 // Both S1 and S2 may be NULL.(
91 TmpInstruction::TmpInstruction(const Type *Ty, Value *s1, Value* s2,
92 const std::string &name)
93 : Instruction(Ty, Instruction::UserOp1, name) {
94 if (s1) { Operands.push_back(Use(s1, this)); }
95 if (s2) { Operands.push_back(Use(s2, this)); }
97 // TmpInstructions should not be garbage checked.
98 LeakDetector::removeGarbageObject(this);
102 bool InstructionSelection::runOnFunction(Function &F)
105 // Build the instruction trees to be given as inputs to BURG.
107 InstrForest instrForest(&F);
109 if (SelectDebugLevel >= Select_DebugInstTrees)
111 cerr << "\n\n*** Input to instruction selection for function "
112 << F.getName() << "\n\n" << F
113 << "\n\n*** Instruction trees for function "
114 << F.getName() << "\n\n";
119 // Invoke BURG instruction selection for each tree
121 for (InstrForest::const_root_iterator RI = instrForest.roots_begin();
122 RI != instrForest.roots_end(); ++RI)
124 InstructionNode* basicNode = *RI;
125 assert(basicNode->parent() == NULL && "A `root' node has a parent?");
127 // Invoke BURM to label each tree node with a state
128 burm_label(basicNode);
130 if (SelectDebugLevel >= Select_DebugBurgTrees)
132 printcover(basicNode, 1, 0);
133 cerr << "\nCover cost == " << treecost(basicNode, 1, 0) << "\n\n";
134 printMatches(basicNode);
137 // Then recursively walk the tree to select instructions
138 SelectInstructionsForTree(basicNode, /*goalnt*/1);
142 // Create the MachineBasicBlock records and add all of the MachineInstrs
143 // defined in the MachineCodeForInstruction objects to also live in the
144 // MachineBasicBlock objects.
146 MachineFunction &MF = MachineFunction::get(&F);
147 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
148 MachineBasicBlock *MCBB = new MachineBasicBlock(BI);
149 MF.getBasicBlockList().push_back(MCBB);
151 for (BasicBlock::iterator II = BI->begin(); II != BI->end(); ++II) {
152 MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(II);
153 MCBB->insert(MCBB->end(), mvec.begin(), mvec.end());
157 // Insert phi elimination code
158 InsertCodeForPhis(F);
160 if (SelectDebugLevel >= Select_PrintMachineCode)
162 cerr << "\n*** Machine instructions after INSTRUCTION SELECTION\n";
163 MachineFunction::get(&F).dump();
170 //-------------------------------------------------------------------------
171 // This method inserts phi elimination code for all BBs in a method
172 //-------------------------------------------------------------------------
175 InstructionSelection::InsertCodeForPhis(Function &F)
177 // for all basic blocks in function
179 MachineFunction &MF = MachineFunction::get(&F);
180 for (MachineFunction::iterator BB = MF.begin(); BB != MF.end(); ++BB) {
181 for (BasicBlock::iterator IIt = BB->getBasicBlock()->begin();
182 PHINode *PN = dyn_cast<PHINode>(&*IIt); ++IIt) {
183 // FIXME: This is probably wrong...
184 Value *PhiCpRes = new PHINode(PN->getType(), "PhiCp:");
186 // The leak detector shouldn't track these nodes. They are not garbage,
187 // even though their parent field is never filled in.
189 LeakDetector::removeGarbageObject(PhiCpRes);
191 // for each incoming value of the phi, insert phi elimination
193 for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i) {
194 // insert the copy instruction to the predecessor BB
195 vector<MachineInstr*> mvec, CpVec;
196 Target.getRegInfo().cpValue2Value(PN->getIncomingValue(i), PhiCpRes,
198 for (vector<MachineInstr*>::iterator MI=mvec.begin();
199 MI != mvec.end(); ++MI) {
200 vector<MachineInstr*> CpVec2 =
201 FixConstantOperandsForInstr(PN, *MI, Target);
202 CpVec2.push_back(*MI);
203 CpVec.insert(CpVec.end(), CpVec2.begin(), CpVec2.end());
206 InsertPhiElimInstructions(PN->getIncomingBlock(i), CpVec);
209 vector<MachineInstr*> mvec;
210 Target.getRegInfo().cpValue2Value(PhiCpRes, PN, mvec);
211 BB->insert(BB->begin(), mvec.begin(), mvec.end());
212 } // for each Phi Instr in BB
213 } // for all BBs in function
216 //-------------------------------------------------------------------------
217 // Thid method inserts a copy instruction to a predecessor BB as a result
218 // of phi elimination.
219 //-------------------------------------------------------------------------
222 InstructionSelection::InsertPhiElimInstructions(BasicBlock *BB,
223 const vector<MachineInstr*>& CpVec)
225 Instruction *TermInst = (Instruction*)BB->getTerminator();
226 MachineCodeForInstruction &MC4Term = MachineCodeForInstruction::get(TermInst);
227 MachineInstr *FirstMIOfTerm = MC4Term.front();
228 assert (FirstMIOfTerm && "No Machine Instrs for terminator");
230 MachineFunction &MF = MachineFunction::get(BB->getParent());
231 MachineBasicBlock *MBB;
233 // FIXME: if PHI instructions existed in the machine code, this would be
235 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
236 if (I->getBasicBlock() == BB) {
241 // find the position of first machine instruction generated by the
242 // terminator of this BB
243 MachineBasicBlock::iterator MCIt =
244 std::find(MBB->begin(), MBB->end(), FirstMIOfTerm);
246 assert(MCIt != MBB->end() && "Start inst of terminator not found");
248 // insert the copy instructions just before the first machine instruction
249 // generated for the terminator
250 MBB->insert(MCIt, CpVec.begin(), CpVec.end());
254 //---------------------------------------------------------------------------
255 // Function SelectInstructionsForTree
257 // Recursively walk the tree to select instructions.
258 // Do this top-down so that child instructions can exploit decisions
259 // made at the child instructions.
261 // E.g., if br(setle(reg,const)) decides the constant is 0 and uses
262 // a branch-on-integer-register instruction, then the setle node
263 // can use that information to avoid generating the SUBcc instruction.
265 // Note that this cannot be done bottom-up because setle must do this
266 // only if it is a child of the branch (otherwise, the result of setle
267 // may be used by multiple instructions).
268 //---------------------------------------------------------------------------
271 InstructionSelection::SelectInstructionsForTree(InstrTreeNode* treeRoot,
274 // Get the rule that matches this node.
276 int ruleForNode = burm_rule(treeRoot->state, goalnt);
278 if (ruleForNode == 0) {
279 cerr << "Could not match instruction tree for instr selection\n";
283 // Get this rule's non-terminals and the corresponding child nodes (if any)
285 short *nts = burm_nts[ruleForNode];
287 // First, select instructions for the current node and rule.
288 // (If this is a list node, not an instruction, then skip this step).
289 // This function is specific to the target architecture.
291 if (treeRoot->opLabel != VRegListOp)
293 vector<MachineInstr*> minstrVec;
295 InstructionNode* instrNode = (InstructionNode*)treeRoot;
296 assert(instrNode->getNodeType() == InstrTreeNode::NTInstructionNode);
298 GetInstructionsByRule(instrNode, ruleForNode, nts, Target, minstrVec);
300 MachineCodeForInstruction &mvec =
301 MachineCodeForInstruction::get(instrNode->getInstruction());
302 mvec.insert(mvec.end(), minstrVec.begin(), minstrVec.end());
305 // Then, recursively compile the child nodes, if any.
308 { // i.e., there is at least one kid
309 InstrTreeNode* kids[2];
310 int currentRule = ruleForNode;
311 burm_kids(treeRoot, currentRule, kids);
313 // First skip over any chain rules so that we don't visit
314 // the current node again.
316 while (ThisIsAChainRule(currentRule))
318 currentRule = burm_rule(treeRoot->state, nts[0]);
319 nts = burm_nts[currentRule];
320 burm_kids(treeRoot, currentRule, kids);
323 // Now we have the first non-chain rule so we have found
324 // the actual child nodes. Recursively compile them.
326 for (unsigned i = 0; nts[i]; i++)
329 InstrTreeNode::InstrTreeNodeType nodeType = kids[i]->getNodeType();
330 if (nodeType == InstrTreeNode::NTVRegListNode ||
331 nodeType == InstrTreeNode::NTInstructionNode)
332 SelectInstructionsForTree(kids[i], nts[i]);
336 // Finally, do any postprocessing on this node after its children
337 // have been translated
339 if (treeRoot->opLabel != VRegListOp)
340 PostprocessMachineCodeForTree((InstructionNode*)treeRoot, ruleForNode, nts);
343 //---------------------------------------------------------------------------
344 // Function PostprocessMachineCodeForTree
346 // Apply any final cleanups to machine code for the root of a subtree
347 // after selection for all its children has been completed.
350 InstructionSelection::PostprocessMachineCodeForTree(InstructionNode* instrNode,
354 // Fix up any constant operands in the machine instructions to either
355 // use an immediate field or to load the constant into a register
356 // Walk backwards and use direct indexes to allow insertion before current
358 Instruction* vmInstr = instrNode->getInstruction();
359 MachineCodeForInstruction &mvec = MachineCodeForInstruction::get(vmInstr);
360 for (unsigned i = mvec.size(); i != 0; --i)
362 vector<MachineInstr*> loadConstVec =
363 FixConstantOperandsForInstr(vmInstr, mvec[i-1], Target);
365 mvec.insert(mvec.begin()+i-1, loadConstVec.begin(), loadConstVec.end());
371 //===----------------------------------------------------------------------===//
372 // createInstructionSelectionPass - Public entrypoint for instruction selection
373 // and this file as a whole...
375 Pass *createInstructionSelectionPass(TargetMachine &T) {
376 return new InstructionSelection(T);