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 static AnnotationID CPFM_AID(
56 AnnotationManager::getID("CodeGen::ConstantPoolForModule"));
58 class ConstantPoolForModule: private Annotation, public NonCopyable {
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
65 static ConstantPoolForModule& get(Module* M) {
66 ConstantPoolForModule* cpool =
67 (ConstantPoolForModule*) M->getAnnotation(CPFM_AID);
68 if (cpool == NULL) // create a new annotation and add it to the Module
69 M->addAnnotation(cpool = new ConstantPoolForModule(M));
73 GlobalVariable* getGlobalForConstant(Constant* CV) {
74 std::map<const Constant*, GlobalVariable*>::iterator I = gvars.find(CV);
76 return I->second; // global exists so return it
77 return addToConstantPool(CV); // create a new global and return it
80 GlobalVariable* addToConstantPool(Constant* CV) {
81 GlobalVariable*& GV = gvars[CV]; // handle to global var entry in map
83 { // check if a global constant already existed; otherwise create one
84 std::map<const Constant*, GlobalVariable*>::iterator PI =
86 if (PI != origGVars.end())
87 GV = PI->second; // put in map
90 GV = new GlobalVariable(CV->getType(), true, //put in map
91 GlobalValue::InternalLinkage, CV);
92 myModule->getGlobalList().push_back(GV); // GV owned by module now
100 ConstantPoolForModule::ConstantPoolForModule(Module* M)
101 : Annotation(CPFM_AID), myModule(M)
103 // Build reverse map for pre-existing global constants so we can find them
104 for (Module::giterator GI = M->gbegin(), GE = M->gend(); GI != GE; ++GI)
105 if (GI->hasInitializer() && GI->isConstant())
106 origGVars[GI->getInitializer()] = GI;
109 //===--------------------------------------------------------------------===//
110 // PreSelection Pass - Specialize LLVM code for the current target machine.
111 // This was and will be a basicblock pass, but make it a FunctionPass until
112 // BasicBlockPass ::doFinalization(Function&) is available.
114 class PreSelection : public BasicBlockPass, public InstVisitor<PreSelection>
116 const TargetMachine ⌖
119 GlobalVariable* getGlobalForConstant(Constant* CV) {
120 Module* M = function->getParent();
121 return ConstantPoolForModule::get(M).getGlobalForConstant(CV);
125 PreSelection (const TargetMachine &T): target(T), function(NULL) {}
127 // runOnBasicBlock - apply this pass to each BB
128 bool runOnBasicBlock(BasicBlock &BB) {
129 function = BB.getParent();
134 bool doFinalization(Function &F) {
135 if (PreSelectDebugLevel >= PreSelect_PrintOutput)
136 std::cerr << "\n\n*** LLVM code after pre-selection for function "
137 << F.getName() << ":\n\n" << F;
141 // These methods do the actual work of specializing code
142 void visitInstruction(Instruction &I); // common work for every instr.
143 void visitGetElementPtrInst(GetElementPtrInst &I);
144 void visitLoadInst(LoadInst &I);
145 void visitCastInst(CastInst &I);
146 void visitStoreInst(StoreInst &I);
148 // Helper functions for visiting operands of every instruction
149 void visitOperands(Instruction &I); // work on all operands of instr.
150 void visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
151 Instruction& insertBefore); // iworks on one operand
154 // Register the pass...
155 RegisterOpt<PreSelection> X("preselect",
156 "Specialize LLVM code for a target machine",
157 createPreSelectionPass);
158 } // end anonymous namespace
161 //------------------------------------------------------------------------------
162 // Helper functions used by methods of class PreSelection
163 //------------------------------------------------------------------------------
166 // getGlobalAddr(): Put address of a global into a v. register.
167 static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
169 if (isa<ConstantPointerRef>(ptr))
170 ptr = cast<ConstantPointerRef>(ptr)->getValue();
172 return (isa<GlobalValue>(ptr))
173 ? new GetElementPtrInst(ptr,
174 std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
175 "addrOfGlobal", &insertBefore)
180 // Wrapper on Constant::classof to use in find_if :-(
181 inline static bool nonConstant(const Use& U)
183 return ! isa<Constant>(U);
187 static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
188 Instruction& insertBefore)
190 Value *getArg1, *getArg2;
192 switch(CE->getOpcode())
194 case Instruction::Cast:
195 getArg1 = CE->getOperand(0);
196 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
197 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
198 return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);
200 case Instruction::GetElementPtr:
201 assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
202 && "All indices in ConstantExpr getelementptr must be constant!");
203 getArg1 = CE->getOperand(0);
204 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
205 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
206 else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
208 return new GetElementPtrInst(getArg1,
209 std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
210 "constantGEP", &insertBefore);
212 default: // must be a binary operator
213 assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
214 CE->getOpcode() < Instruction::BinaryOpsEnd &&
215 "Unrecognized opcode in ConstantExpr");
216 getArg1 = CE->getOperand(0);
217 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
218 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
219 getArg2 = CE->getOperand(1);
220 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
221 getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
222 return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
224 "constantBinaryOp", &insertBefore);
229 //------------------------------------------------------------------------------
230 // Instruction visitor methods to perform instruction-specific operations
231 //------------------------------------------------------------------------------
233 // Common work for *all* instructions. This needs to be called explicitly
234 // by other visit<InstructionType> functions.
236 PreSelection::visitInstruction(Instruction &I)
238 visitOperands(I); // Perform operand transformations
242 // GetElementPtr instructions: check if pointer is a global
244 PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
246 // Check for a global and put its address into a register before this instr
247 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
248 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
250 // Decompose multidimensional array references
251 DecomposeArrayRef(&I);
253 // Perform other transformations common to all instructions
258 // Load instructions: check if pointer is a global
260 PreSelection::visitLoadInst(LoadInst &I)
262 // Check for a global and put its address into a register before this instr
263 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
264 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
266 // Perform other transformations common to all instructions
271 // Store instructions: check if pointer is a global
273 PreSelection::visitStoreInst(StoreInst &I)
275 // Check for a global and put its address into a register before this instr
276 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
277 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
279 // Perform other transformations common to all instructions
284 // Cast instructions:
285 // -- check if argument is a global
286 // -- make multi-step casts explicit:
287 // -- float/double to uint32_t:
288 // If target does not have a float-to-unsigned instruction, we
289 // need to convert to uint64_t and then to uint32_t, or we may
290 // overflow the signed int representation for legal uint32_t
291 // values. Expand this without checking target.
294 PreSelection::visitCastInst(CastInst &I)
296 CastInst* castI = NULL;
298 // Check for a global and put its address into a register before this instr
299 if (GetElementPtrInst* gep = getGlobalAddr(I.getOperand(0), I))
301 I.setOperand(0, gep); // replace pointer operand
303 else if (I.getType() == Type::UIntTy &&
304 I.getOperand(0)->getType()->isFloatingPoint())
305 { // insert a cast-fp-to-long before I, and then replace the operand of I
306 castI = new CastInst(I.getOperand(0), Type::LongTy, "fp2Long2Uint", &I);
307 I.setOperand(0, castI); // replace fp operand with long
310 // Perform other transformations common to all instructions
313 visitInstruction(*castI);
317 // visitOperands() transforms individual operands of all instructions:
318 // -- Load "large" int constants into a virtual register. What is large
319 // depends on the type of instruction and on the target architecture.
320 // -- For any constants that cannot be put in an immediate field,
321 // load address into virtual register first, and then load the constant.
324 PreSelection::visitOperands(Instruction &I)
326 // For any instruction other than PHI, copies go just before the instr.
327 // For a PHI, operand copies must be before the terminator of the
328 // appropriate predecessor basic block. Remaining logic is simple
329 // so just handle PHIs and other instructions separately.
331 if (PHINode* phi = dyn_cast<PHINode>(&I))
333 for (unsigned i=0, N=phi->getNumIncomingValues(); i < N; ++i)
334 if (Constant* CV = dyn_cast<Constant>(phi->getIncomingValue(i)))
335 this->visitOneOperand(I, CV, phi->getOperandNumForIncomingValue(i),
336 * phi->getIncomingBlock(i)->getTerminator());
339 for (unsigned i=0, N=I.getNumOperands(); i < N; ++i)
340 if (Constant* CV = dyn_cast<Constant>(I.getOperand(i)))
341 this->visitOneOperand(I, CV, i, I);
345 PreSelection::visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
346 Instruction& insertBefore)
348 if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
349 { // load-time constant: factor it out so we optimize as best we can
350 Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
351 I.setOperand(opNum, computeConst); // replace expr operand with result
353 else if (target.getInstrInfo().ConstantTypeMustBeLoaded(CV))
354 { // load address of constant into a register, then load the constant
355 GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
357 LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
358 I.setOperand(opNum, ldI); // replace operand with copy in v.reg.
360 else if (target.getInstrInfo().ConstantMayNotFitInImmedField(CV, &I))
361 { // put the constant into a virtual register using a cast
362 CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
364 I.setOperand(opNum, castI); // replace operand with copy in v.reg.
369 //===----------------------------------------------------------------------===//
370 // createPreSelectionPass - Public entrypoint for pre-selection pass
371 // and this file as a whole...
374 createPreSelectionPass(TargetMachine &T)
376 return new PreSelection(T);