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 "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,true,CV); //put in map
91 myModule->getGlobalList().push_back(GV); // GV owned by module now
99 ConstantPoolForModule::ConstantPoolForModule(Module* M)
100 : Annotation(CPFM_AID), myModule(M)
102 // Build reverse map for pre-existing global constants so we can find them
103 for (Module::giterator GI = M->gbegin(), GE = M->gend(); GI != GE; ++GI)
104 if (GI->hasInitializer() && GI->isConstant())
105 origGVars[GI->getInitializer()] = GI;
108 //===--------------------------------------------------------------------===//
109 // PreSelection Pass - Specialize LLVM code for the current target machine.
110 // This was and will be a basicblock pass, but make it a FunctionPass until
111 // BasicBlockPass ::doFinalization(Function&) is available.
113 class PreSelection : public BasicBlockPass, public InstVisitor<PreSelection>
115 const TargetMachine ⌖
118 GlobalVariable* getGlobalForConstant(Constant* CV) {
119 Module* M = function->getParent();
120 return ConstantPoolForModule::get(M).getGlobalForConstant(CV);
124 PreSelection (const TargetMachine &T): target(T), function(NULL) {}
126 // runOnBasicBlock - apply this pass to each BB
127 bool runOnBasicBlock(BasicBlock &BB) {
128 function = BB.getParent();
133 bool doFinalization(Function &F) {
134 if (PreSelectDebugLevel >= PreSelect_PrintOutput)
135 std::cerr << "\n\n*** LLVM code after pre-selection for function "
136 << F.getName() << ":\n\n" << F;
140 // These methods do the actual work of specializing code
141 void visitInstruction(Instruction &I); // common work for every instr.
142 void visitGetElementPtrInst(GetElementPtrInst &I);
143 void visitLoadInst(LoadInst &I);
144 void visitCastInst(CastInst &I);
145 void visitStoreInst(StoreInst &I);
147 // Helper functions for visiting operands of every instruction
148 void visitOperands(Instruction &I); // work on all operands of instr.
149 void visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
150 Instruction& insertBefore); // iworks on one operand
152 } // end anonymous namespace
155 // Register the pass...
156 static RegisterOpt<PreSelection> X("preselect",
157 "Specialize LLVM code for a target machine",
158 createPreSelectionPass);
160 //------------------------------------------------------------------------------
161 // Helper functions used by methods of class PreSelection
162 //------------------------------------------------------------------------------
165 // getGlobalAddr(): Put address of a global into a v. register.
166 static GetElementPtrInst* getGlobalAddr(Value* ptr, Instruction& insertBefore)
168 if (isa<ConstantPointerRef>(ptr))
169 ptr = cast<ConstantPointerRef>(ptr)->getValue();
171 return (isa<GlobalValue>(ptr))
172 ? new GetElementPtrInst(ptr,
173 std::vector<Value*>(1, ConstantSInt::get(Type::LongTy, 0U)),
174 "addrOfGlobal", &insertBefore)
179 // Wrapper on Constant::classof to use in find_if :-(
180 inline static bool nonConstant(const Use& U)
182 return ! isa<Constant>(U);
186 static Instruction* DecomposeConstantExpr(ConstantExpr* CE,
187 Instruction& insertBefore)
189 Value *getArg1, *getArg2;
191 switch(CE->getOpcode())
193 case Instruction::Cast:
194 getArg1 = CE->getOperand(0);
195 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
196 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
197 return new CastInst(getArg1, CE->getType(), "constantCast",&insertBefore);
199 case Instruction::GetElementPtr:
200 assert(find_if(CE->op_begin()+1, CE->op_end(),nonConstant) == CE->op_end()
201 && "All indices in ConstantExpr getelementptr must be constant!");
202 getArg1 = CE->getOperand(0);
203 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
204 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
205 else if (GetElementPtrInst* gep = getGlobalAddr(getArg1, insertBefore))
207 return new GetElementPtrInst(getArg1,
208 std::vector<Value*>(CE->op_begin()+1, CE->op_end()),
209 "constantGEP", &insertBefore);
211 default: // must be a binary operator
212 assert(CE->getOpcode() >= Instruction::BinaryOpsBegin &&
213 CE->getOpcode() < Instruction::BinaryOpsEnd &&
214 "Unrecognized opcode in ConstantExpr");
215 getArg1 = CE->getOperand(0);
216 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg1))
217 getArg1 = DecomposeConstantExpr(CEarg, insertBefore);
218 getArg2 = CE->getOperand(1);
219 if (ConstantExpr* CEarg = dyn_cast<ConstantExpr>(getArg2))
220 getArg2 = DecomposeConstantExpr(CEarg, insertBefore);
221 return BinaryOperator::create((Instruction::BinaryOps) CE->getOpcode(),
223 "constantBinaryOp", &insertBefore);
228 //------------------------------------------------------------------------------
229 // Instruction visitor methods to perform instruction-specific operations
230 //------------------------------------------------------------------------------
232 // Common work for *all* instructions. This needs to be called explicitly
233 // by other visit<InstructionType> functions.
235 PreSelection::visitInstruction(Instruction &I)
237 visitOperands(I); // Perform operand transformations
241 // GetElementPtr instructions: check if pointer is a global
243 PreSelection::visitGetElementPtrInst(GetElementPtrInst &I)
245 // Check for a global and put its address into a register before this instr
246 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
247 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
249 // Decompose multidimensional array references
250 DecomposeArrayRef(&I);
252 // Perform other transformations common to all instructions
257 // Load instructions: check if pointer is a global
259 PreSelection::visitLoadInst(LoadInst &I)
261 // Check for a global and put its address into a register before this instr
262 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
263 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
265 // Perform other transformations common to all instructions
270 // Store instructions: check if pointer is a global
272 PreSelection::visitStoreInst(StoreInst &I)
274 // Check for a global and put its address into a register before this instr
275 if (GetElementPtrInst* gep = getGlobalAddr(I.getPointerOperand(), I))
276 I.setOperand(I.getPointerOperandIndex(), gep); // replace pointer operand
278 // Perform other transformations common to all instructions
283 // Cast instructions:
284 // -- check if argument is a global
285 // -- make multi-step casts explicit:
286 // -- float/double to uint32_t:
287 // If target does not have a float-to-unsigned instruction, we
288 // need to convert to uint64_t and then to uint32_t, or we may
289 // overflow the signed int representation for legal uint32_t
290 // values. Expand this without checking target.
293 PreSelection::visitCastInst(CastInst &I)
295 CastInst* castI = NULL;
297 // Check for a global and put its address into a register before this instr
298 if (GetElementPtrInst* gep = getGlobalAddr(I.getOperand(0), I))
300 I.setOperand(0, gep); // replace pointer operand
302 else if (I.getType() == Type::UIntTy &&
303 I.getOperand(0)->getType()->isFloatingPoint())
304 { // insert a cast-fp-to-long before I, and then replace the operand of I
305 castI = new CastInst(I.getOperand(0), Type::LongTy, "fp2Long2Uint", &I);
306 I.setOperand(0, castI); // replace fp operand with long
309 // Perform other transformations common to all instructions
312 visitInstruction(*castI);
316 // visitOperands() transforms individual operands of all instructions:
317 // -- Load "large" int constants into a virtual register. What is large
318 // depends on the type of instruction and on the target architecture.
319 // -- For any constants that cannot be put in an immediate field,
320 // load address into virtual register first, and then load the constant.
323 PreSelection::visitOperands(Instruction &I)
325 // For any instruction other than PHI, copies go just before the instr.
326 // For a PHI, operand copies must be before the terminator of the
327 // appropriate predecessor basic block. Remaining logic is simple
328 // so just handle PHIs and other instructions separately.
330 if (PHINode* phi = dyn_cast<PHINode>(&I))
332 for (unsigned i=0, N=phi->getNumIncomingValues(); i < N; ++i)
333 if (Constant* CV = dyn_cast<Constant>(phi->getIncomingValue(i)))
334 this->visitOneOperand(I, CV, phi->getOperandNumForIncomingValue(i),
335 * phi->getIncomingBlock(i)->getTerminator());
338 for (unsigned i=0, N=I.getNumOperands(); i < N; ++i)
339 if (Constant* CV = dyn_cast<Constant>(I.getOperand(i)))
340 this->visitOneOperand(I, CV, i, I);
344 PreSelection::visitOneOperand(Instruction &I, Constant* CV, unsigned opNum,
345 Instruction& insertBefore)
347 if (ConstantExpr* CE = dyn_cast<ConstantExpr>(CV))
348 { // load-time constant: factor it out so we optimize as best we can
349 Instruction* computeConst = DecomposeConstantExpr(CE, insertBefore);
350 I.setOperand(opNum, computeConst); // replace expr operand with result
352 else if (target.getInstrInfo().ConstantTypeMustBeLoaded(CV))
353 { // load address of constant into a register, then load the constant
354 GetElementPtrInst* gep = getGlobalAddr(getGlobalForConstant(CV),
356 LoadInst* ldI = new LoadInst(gep, "loadConst", &insertBefore);
357 I.setOperand(opNum, ldI); // replace operand with copy in v.reg.
359 else if (target.getInstrInfo().ConstantMayNotFitInImmedField(CV, &I))
360 { // put the constant into a virtual register using a cast
361 CastInst* castI = new CastInst(CV, CV->getType(), "copyConst",
363 I.setOperand(opNum, castI); // replace operand with copy in v.reg.
368 //===----------------------------------------------------------------------===//
369 // createPreSelectionPass - Public entrypoint for pre-selection pass
370 // and this file as a whole...
373 createPreSelectionPass(TargetMachine &T)
375 return new PreSelection(T);