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/MachineInstrInfo.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 "llvm/Annotation.h"
24 #include "Support/CommandLine.h"
25 #include "Support/NonCopyable.h"
30 //===--------------------------------------------------------------------===//
31 // SelectDebugLevel - Allow command line control over debugging.
33 enum PreSelectDebugLevel_t {
34 PreSelect_NoDebugInfo,
35 PreSelect_PrintOutput,
38 // Enable Debug Options to be specified on the command line
39 cl::opt<PreSelectDebugLevel_t>
40 PreSelectDebugLevel("dpreselect", cl::Hidden,
41 cl::desc("debug information for target-dependent pre-selection"),
43 clEnumValN(PreSelect_NoDebugInfo, "n", "disable debug output (default)"),
44 clEnumValN(PreSelect_PrintOutput, "y", "print generated machine code"),
45 /* default level = */ PreSelect_NoDebugInfo));
48 //===--------------------------------------------------------------------===//
49 // class ConstantPoolForModule:
51 // The pool of constants that must be emitted for a module.
52 // This is a single pool for the entire module and is shared by
53 // all invocations of the PreSelection pass for this module by putting
54 // this as an annotation on the Module object.
55 // A single GlobalVariable is created for each constant in the pool
56 // representing the memory for that constant.
58 static AnnotationID CPFM_AID(
59 AnnotationManager::getID("CodeGen::ConstantPoolForModule"));
61 class ConstantPoolForModule: private Annotation, public NonCopyable {
63 std::map<const Constant*, GlobalVariable*> gvars;
64 std::map<const Constant*, GlobalVariable*> origGVars;
65 ConstantPoolForModule(Module* M); // called only by annotation builder
66 ConstantPoolForModule(); // do not implement
68 static ConstantPoolForModule& get(Module* M) {
69 ConstantPoolForModule* cpool =
70 (ConstantPoolForModule*) M->getAnnotation(CPFM_AID);
71 if (cpool == NULL) // create a new annotation and add it to the Module
72 M->addAnnotation(cpool = new ConstantPoolForModule(M));
76 GlobalVariable* getGlobalForConstant(Constant* CV) {
77 std::map<const Constant*, GlobalVariable*>::iterator I = gvars.find(CV);
79 return I->second; // global exists so return it
80 return addToConstantPool(CV); // create a new global and return it
83 GlobalVariable* addToConstantPool(Constant* CV) {
84 GlobalVariable*& GV = gvars[CV]; // handle to global var entry in map
86 { // check if a global constant already existed; otherwise create one
87 std::map<const Constant*, GlobalVariable*>::iterator PI =
89 if (PI != origGVars.end())
90 GV = PI->second; // put in map
93 GV = new GlobalVariable(CV->getType(), true,true,CV); //put in map
94 myModule->getGlobalList().push_back(GV); // GV owned by module now
102 ConstantPoolForModule::ConstantPoolForModule(Module* M)
103 : Annotation(CPFM_AID), myModule(M)
105 // Build reverse map for pre-existing global constants so we can find them
106 for (Module::giterator GI = M->gbegin(), GE = M->gend(); GI != GE; ++GI)
107 if (GI->hasInitializer() && GI->isConstant())
108 origGVars[GI->getInitializer()] = GI;
111 //===--------------------------------------------------------------------===//
112 // PreSelection Pass - Specialize LLVM code for the current target machine.
113 // This was and will be a basicblock pass, but make it a FunctionPass until
114 // BasicBlockPass ::doFinalization(Function&) is available.
116 class PreSelection : public BasicBlockPass, public InstVisitor<PreSelection>
118 const TargetMachine ⌖
121 GlobalVariable* getGlobalForConstant(Constant* CV) {
122 Module* M = function->getParent();
123 return ConstantPoolForModule::get(M).getGlobalForConstant(CV);
127 PreSelection (const TargetMachine &T): target(T), function(NULL) {}
129 // runOnBasicBlock - apply this pass to each BB
130 bool runOnBasicBlock(BasicBlock &BB) {
131 function = BB.getParent();
136 bool doFinalization(Function &F) {
137 if (PreSelectDebugLevel >= PreSelect_PrintOutput)
138 cerr << "\n\n*** LLVM code after pre-selection for function "
139 << F.getName() << ":\n\n" << F;
143 // These methods do the actual work of specializing code
144 void visitInstruction(Instruction &I); // common work for every instr.
145 void visitGetElementPtrInst(GetElementPtrInst &I);
146 void visitLoadInst(LoadInst &I);
147 void visitCastInst(CastInst &I);
148 void visitStoreInst(StoreInst &I);
150 // Helper functions for visiting operands of every instruction
151 void visitOperands(Instruction &I); // work on all operands of instr.
152 void visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
153 Instruction& insertBefore); // iworks on one operand
155 } // end anonymous namespace
158 // Register the pass...
159 static RegisterOpt<PreSelection> X("preselect",
160 "Specialize LLVM code for a target machine",
161 createPreSelectionPass);
163 //------------------------------------------------------------------------------
164 // Helper functions used by methods of class PreSelection
165 //------------------------------------------------------------------------------
168 // getGlobalAddr(): Put address of a global into a v. register.
169 static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
171 if (isa<ConstantPointerRef>(ptr))
172 ptr = cast<ConstantPointerRef>(ptr)->getValue();
174 return (isa<GlobalValue>(ptr))
175 ? new GetElementPtrInst(ptr,
176 std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
177 "addrOfGlobal", &insertBefore)
182 // Wrapper on Constant::classof to use in find_if :-(
183 inline static bool nonConstant(const Use& U)
185 return ! isa<Constant>(U);
189 static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
190 Instruction& insertBefore)
192 Value *getArg1, *getArg2;
194 switch(CE->getOpcode())
196 case Instruction::Cast:
197 getArg1 = CE->getOperand(0);
198 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
199 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
200 return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);
202 case Instruction::GetElementPtr:
203 assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
204 && "All indices in ConstantExpr getelementptr must be constant!");
205 getArg1 = CE->getOperand(0);
206 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
207 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
208 else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
210 return new GetElementPtrInst(getArg1,
211 std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
212 "constantGEP", &insertBefore);
214 default: // must be a binary operator
215 assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
216 CE->getOpcode() < Instruction::BinaryOpsEnd &&
217 "Unrecognized opcode in ConstantExpr");
218 getArg1 = CE->getOperand(0);
219 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
220 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
221 getArg2 = CE->getOperand(1);
222 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
223 getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
224 return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
226 "constantBinaryOp", &insertBefore);
231 //------------------------------------------------------------------------------
232 // Instruction visitor methods to perform instruction-specific operations
233 //------------------------------------------------------------------------------
235 // Common work for *all* instructions. This needs to be called explicitly
236 // by other visit<InstructionType> functions.
238 PreSelection::visitInstruction(Instruction &I)
240 visitOperands(I); // Perform operand transformations
244 // GetElementPtr instructions: check if pointer is a global
246 PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
248 // Check for a global and put its address into a register before this instr
249 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
250 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
252 // Decompose multidimensional array references
253 DecomposeArrayRef(&I);
255 // Perform other transformations common to all instructions
260 // Load instructions: check if pointer is a global
262 PreSelection::visitLoadInst(LoadInst &I)
264 // Check for a global and put its address into a register before this instr
265 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
266 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
268 // Perform other transformations common to all instructions
273 // Store instructions: check if pointer is a global
275 PreSelection::visitStoreInst(StoreInst &I)
277 // Check for a global and put its address into a register before this instr
278 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
279 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
281 // Perform other transformations common to all instructions
286 // Cast instructions:
287 // -- check if argument is a global
288 // -- make multi-step casts explicit:
289 // -- float/double to uint32_t:
290 // If target does not have a float-to-unsigned instruction, we
291 // need to convert to uint64_t and then to uint32_t, or we may
292 // overflow the signed int representation for legal uint32_t
293 // values. Expand this without checking target.
296 PreSelection::visitCastInst(CastInst &I)
298 CastInst* castI = NULL;
300 // Check for a global and put its address into a register before this instr
301 if (GetElementPtrInst* gep = getGlobalAddr(I.getOperand(0), I))
303 I.setOperand(0, gep); // replace pointer operand
305 else if (I.getType() == Type::UIntTy &&
306 I.getOperand(0)->getType()->isFloatingPoint())
307 { // insert a cast-fp-to-long before I, and then replace the operand of I
308 castI = new CastInst(I.getOperand(0), Type::LongTy, "fp2Long2Uint", &I);
309 I.setOperand(0, castI); // replace fp operand with long
312 // Perform other transformations common to all instructions
315 visitInstruction(*castI);
319 // visitOperands() transforms individual operands of all instructions:
320 // -- Load "large" int constants into a virtual register. What is large
321 // depends on the type of instruction and on the target architecture.
322 // -- For any constants that cannot be put in an immediate field,
323 // load address into virtual register first, and then load the constant.
326 PreSelection::visitOperands(Instruction &I)
328 // For any instruction other than PHI, copies go just before the instr.
329 // For a PHI, operand copies must be before the terminator of the
330 // appropriate predecessor basic block. Remaining logic is simple
331 // so just handle PHIs and other instructions separately.
333 if (PHINode* phi = dyn_cast<PHINode>(&I))
335 for (unsigned i=0, N=phi->getNumIncomingValues(); i < N; ++i)
336 if (Constant* CV = dyn_cast<Constant>(phi->getIncomingValue(i)))
337 this->visitOneOperand(I, CV, phi->getOperandNumForIncomingValue(i),
338 * phi->getIncomingBlock(i)->getTerminator());
341 for (unsigned i=0, N=I.getNumOperands(); i < N; ++i)
342 if (Constant* CV = dyn_cast<Constant>(I.getOperand(i)))
343 this->visitOneOperand(I, CV, i, I);
347 PreSelection::visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
348 Instruction& insertBefore)
350 if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
351 { // load-time constant: factor it out so we optimize as best we can
352 Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
353 I.setOperand(opNum, computeConst); // replace expr operand with result
355 else if (target.getInstrInfo().ConstantTypeMustBeLoaded(CV))
356 { // load address of constant into a register, then load the constant
357 GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
359 LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
360 I.setOperand(opNum, ldI); // replace operand with copy in v.reg.
362 else if (target.getInstrInfo().ConstantMayNotFitInImmedField(CV, &I))
363 { // put the constant into a virtual register using a cast
364 CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
366 I.setOperand(opNum, castI); // replace operand with copy in v.reg.
371 //===----------------------------------------------------------------------===//
372 // createPreSelectionPass - Public entrypoint for pre-selection pass
373 // and this file as a whole...
376 createPreSelectionPass(TargetMachine &T)
378 return new PreSelection(T);