1 //===- PreSelection.cpp - Specialize LLVM code for target machine ---------===//
3 // This file defines the PreSelection pass which specializes LLVM code for a
4 // target machine, while remaining in legal portable LLVM form and
5 // preserving type information and type safety. This is meant to enable
6 // dataflow optimizations on target-specific operations such as accesses to
7 // constants, globals, and array indexing.
9 //===----------------------------------------------------------------------===//
11 #include "llvm/CodeGen/PreSelection.h"
12 #include "llvm/Target/TargetMachine.h"
13 #include "llvm/Target/TargetInstrInfo.h"
14 #include "llvm/Transforms/Scalar.h"
15 #include "llvm/Support/InstVisitor.h"
16 #include "llvm/Module.h"
17 #include "llvm/Constants.h"
18 #include "llvm/iMemory.h"
19 #include "llvm/iPHINode.h"
20 #include "llvm/iOther.h"
21 #include "llvm/DerivedTypes.h"
22 #include "llvm/Pass.h"
23 #include "Support/CommandLine.h"
27 //===--------------------------------------------------------------------===//
28 // SelectDebugLevel - Allow command line control over debugging.
30 enum PreSelectDebugLevel_t {
31 PreSelect_NoDebugInfo,
32 PreSelect_PrintOutput,
35 // Enable Debug Options to be specified on the command line
36 cl::opt<PreSelectDebugLevel_t>
37 PreSelectDebugLevel("dpreselect", cl::Hidden,
38 cl::desc("debug information for target-dependent pre-selection"),
40 clEnumValN(PreSelect_NoDebugInfo, "n", "disable debug output (default)"),
41 clEnumValN(PreSelect_PrintOutput, "y", "print generated machine code"),
42 /* default level = */ PreSelect_NoDebugInfo));
45 //===--------------------------------------------------------------------===//
46 // class ConstantPoolForModule:
48 // The pool of constants that must be emitted for a module.
49 // This is a single pool for the entire module and is shared by
50 // all invocations of the PreSelection pass for this module by putting
51 // this as an annotation on the Module object.
52 // A single GlobalVariable is created for each constant in the pool
53 // representing the memory for that constant.
55 AnnotationID CPFM_AID(
56 AnnotationManager::getID("CodeGen::ConstantPoolForModule"));
58 class ConstantPoolForModule : private Annotation {
60 std::map<const Constant*, GlobalVariable*> gvars;
61 std::map<const Constant*, GlobalVariable*> origGVars;
62 ConstantPoolForModule(Module* M); // called only by annotation builder
63 ConstantPoolForModule(); // DO NOT IMPLEMENT
64 void operator=(const ConstantPoolForModule&); // DO NOT IMPLEMENT
66 static ConstantPoolForModule& get(Module* M) {
67 ConstantPoolForModule* cpool =
68 (ConstantPoolForModule*) M->getAnnotation(CPFM_AID);
69 if (cpool == NULL) // create a new annotation and add it to the Module
70 M->addAnnotation(cpool = new ConstantPoolForModule(M));
74 GlobalVariable* getGlobalForConstant(Constant* CV) {
75 std::map<const Constant*, GlobalVariable*>::iterator I = gvars.find(CV);
77 return I->second; // global exists so return it
78 return addToConstantPool(CV); // create a new global and return it
81 GlobalVariable* addToConstantPool(Constant* CV) {
82 GlobalVariable*& GV = gvars[CV]; // handle to global var entry in map
84 { // check if a global constant already existed; otherwise create one
85 std::map<const Constant*, GlobalVariable*>::iterator PI =
87 if (PI != origGVars.end())
88 GV = PI->second; // put in map
91 GV = new GlobalVariable(CV->getType(), true, //put in map
92 GlobalValue::InternalLinkage, CV);
93 myModule->getGlobalList().push_back(GV); // GV owned by module now
101 ConstantPoolForModule::ConstantPoolForModule(Module* M)
102 : Annotation(CPFM_AID), myModule(M)
104 // Build reverse map for pre-existing global constants so we can find them
105 for (Module::giterator GI = M->gbegin(), GE = M->gend(); GI != GE; ++GI)
106 if (GI->hasInitializer() && GI->isConstant())
107 origGVars[GI->getInitializer()] = GI;
110 //===--------------------------------------------------------------------===//
111 // PreSelection Pass - Specialize LLVM code for the current target machine.
112 // This was and will be a basicblock pass, but make it a FunctionPass until
113 // BasicBlockPass ::doFinalization(Function&) is available.
115 class PreSelection : public BasicBlockPass, public InstVisitor<PreSelection>
117 const TargetMachine ⌖
120 GlobalVariable* getGlobalForConstant(Constant* CV) {
121 Module* M = function->getParent();
122 return ConstantPoolForModule::get(M).getGlobalForConstant(CV);
126 PreSelection (const TargetMachine &T): target(T), function(NULL) {}
128 // runOnBasicBlock - apply this pass to each BB
129 bool runOnBasicBlock(BasicBlock &BB) {
130 function = BB.getParent();
135 bool doFinalization(Function &F) {
136 if (PreSelectDebugLevel >= PreSelect_PrintOutput)
137 std::cerr << "\n\n*** LLVM code after pre-selection for function "
138 << F.getName() << ":\n\n" << F;
142 // These methods do the actual work of specializing code
143 void visitInstruction(Instruction &I); // common work for every instr.
144 void visitGetElementPtrInst(GetElementPtrInst &I);
145 void visitLoadInst(LoadInst &I);
146 void visitCastInst(CastInst &I);
147 void visitCallInst(CallInst &I);
148 void visitStoreInst(StoreInst &I);
150 // Helper functions for visiting operands of every instruction
152 // visitOperands() works on every operand in [firstOp, lastOp-1].
153 // If lastOp==0, lastOp defaults to #operands or #incoming Phi values.
155 // visitOneOperand() does all the work for one operand.
157 void visitOperands(Instruction &I, int firstOp=0, int lastOp=0);
158 void visitOneOperand(Instruction &I, Value* Op, unsigned opNum,
159 Instruction& insertBefore);
162 // Register the pass...
163 RegisterOpt<PreSelection> X("preselect",
164 "Specialize LLVM code for a target machine",
165 createPreSelectionPass);
166 } // end anonymous namespace
169 //------------------------------------------------------------------------------
170 // Helper functions used by methods of class PreSelection
171 //------------------------------------------------------------------------------
174 // getGlobalAddr(): Put address of a global into a v. register.
175 static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
177 if (isa<ConstantPointerRef>(ptr))
178 ptr = cast<ConstantPointerRef>(ptr)->getValue();
180 return (isa<GlobalVariable>(ptr))
181 ? new GetElementPtrInst(ptr,
182 std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
183 "addrOfGlobal", &insertBefore)
188 // Wrapper on Constant::classof to use in find_if :-(
189 inline static bool nonConstant(const Use& U)
191 return ! isa<Constant>(U);
195 static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
196 Instruction& insertBefore)
198 Value *getArg1, *getArg2;
200 switch(CE->getOpcode())
202 case Instruction::Cast:
203 getArg1 = CE->getOperand(0);
204 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
205 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
206 return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);
208 case Instruction::GetElementPtr:
209 assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
210 && "All indices in ConstantExpr getelementptr must be constant!");
211 getArg1 = CE->getOperand(0);
212 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
213 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
214 else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
216 return new GetElementPtrInst(getArg1,
217 std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
218 "constantGEP", &insertBefore);
220 default: // must be a binary operator
221 assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
222 CE->getOpcode() < Instruction::BinaryOpsEnd &&
223 "Unrecognized opcode in ConstantExpr");
224 getArg1 = CE->getOperand(0);
225 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
226 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
227 getArg2 = CE->getOperand(1);
228 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
229 getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
230 return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
232 "constantBinaryOp", &insertBefore);
237 //------------------------------------------------------------------------------
238 // Instruction visitor methods to perform instruction-specific operations
239 //------------------------------------------------------------------------------
241 // Common work for *all* instructions. This needs to be called explicitly
242 // by other visit<InstructionType> functions.
244 PreSelection::visitInstruction(Instruction &I)
246 visitOperands(I); // Perform operand transformations
250 // GetElementPtr instructions: check if pointer is a global
252 PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
254 // Check for a global and put its address into a register before this instr
255 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
256 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
258 // Decompose multidimensional array references
259 DecomposeArrayRef(&I);
261 // Perform other transformations common to all instructions
266 // Load instructions: check if pointer is a global
268 PreSelection::visitLoadInst(LoadInst &I)
270 // Check for a global and put its address into a register before this instr
271 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
272 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
274 // Perform other transformations common to all instructions
279 // Store instructions: check if pointer is a global
281 PreSelection::visitStoreInst(StoreInst &I)
283 // Check for a global and put its address into a register before this instr
284 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
285 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
287 // Perform other transformations common to all instructions
292 // Cast instructions:
293 // -- check if argument is a global
294 // -- make multi-step casts explicit:
295 // -- float/double to uint32_t:
296 // If target does not have a float-to-unsigned instruction, we
297 // need to convert to uint64_t and then to uint32_t, or we may
298 // overflow the signed int representation for legal uint32_t
299 // values. Expand this without checking target.
302 PreSelection::visitCastInst(CastInst &I)
304 CastInst* castI = NULL;
306 // Check for a global and put its address into a register before this instr
307 if (GetElementPtrInst* gep = getGlobalAddr(I.getOperand(0), I))
309 I.setOperand(0, gep); // replace pointer operand
311 else if (I.getType() == Type::UIntTy &&
312 I.getOperand(0)->getType()->isFloatingPoint())
313 { // insert a cast-fp-to-long before I, and then replace the operand of I
314 castI = new CastInst(I.getOperand(0), Type::LongTy, "fp2Long2Uint", &I);
315 I.setOperand(0, castI); // replace fp operand with long
318 // Perform other transformations common to all instructions
321 visitInstruction(*castI);
325 PreSelection::visitCallInst(CallInst &I)
327 // Tell visitOperands to ignore the function name if this is a direct call.
328 visitOperands(I, (/*firstOp=*/ I.getCalledFunction()? 1 : 0));
332 // visitOperands() transforms individual operands of all instructions:
333 // -- Load "large" int constants into a virtual register. What is large
334 // depends on the type of instruction and on the target architecture.
335 // -- For any constants that cannot be put in an immediate field,
336 // load address into virtual register first, and then load the constant.
338 // firstOp and lastOp can be used to skip leading and trailing operands.
339 // If lastOp is 0, it defaults to #operands or #incoming Phi values.
342 PreSelection::visitOperands(Instruction &I, int firstOp, int lastOp)
344 // For any instruction other than PHI, copies go just before the instr.
345 // For a PHI, operand copies must be before the terminator of the
346 // appropriate predecessor basic block. Remaining logic is simple
347 // so just handle PHIs and other instructions separately.
349 if (PHINode* phi = dyn_cast<PHINode>(&I))
352 lastOp = phi->getNumIncomingValues();
353 for (unsigned i=firstOp, N=lastOp; i < N; ++i)
354 this->visitOneOperand(I, phi->getIncomingValue(i),
355 phi->getOperandNumForIncomingValue(i),
356 * phi->getIncomingBlock(i)->getTerminator());
361 lastOp = I.getNumOperands();
362 for (unsigned i=firstOp, N=lastOp; i < N; ++i)
363 this->visitOneOperand(I, I.getOperand(i), i, I);
368 PreSelection::visitOneOperand(Instruction &I, Value* Op, unsigned opNum,
369 Instruction& insertBefore)
371 if (GetElementPtrInst* gep = getGlobalAddr(Op, insertBefore)) {
372 I.setOperand(opNum, gep); // replace global operand
376 Constant* CV = dyn_cast<Constant>(Op);
380 if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
381 { // load-time constant: factor it out so we optimize as best we can
382 Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
383 I.setOperand(opNum, computeConst); // replace expr operand with result
385 else if (target.getInstrInfo().ConstantTypeMustBeLoaded(CV))
386 { // load address of constant into a register, then load the constant
387 GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
389 LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
390 I.setOperand(opNum, ldI); // replace operand with copy in v.reg.
392 else if (target.getInstrInfo().ConstantMayNotFitInImmedField(CV, &I))
393 { // put the constant into a virtual register using a cast
394 CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
396 I.setOperand(opNum, castI); // replace operand with copy in v.reg.
401 //===----------------------------------------------------------------------===//
402 // createPreSelectionPass - Public entrypoint for pre-selection pass
403 // and this file as a whole...
406 createPreSelectionPass(TargetMachine &T)
408 return new PreSelection(T);