1 //===-- InstSelectSimple.cpp - A simple instruction selector for x86 ------===//
3 // This file defines a simple peephole instruction selector for the x86 platform
5 //===----------------------------------------------------------------------===//
8 #include "X86InstrInfo.h"
9 #include "X86InstrBuilder.h"
10 #include "llvm/Function.h"
11 #include "llvm/iTerminators.h"
12 #include "llvm/iOperators.h"
13 #include "llvm/iOther.h"
14 #include "llvm/iPHINode.h"
15 #include "llvm/iMemory.h"
16 #include "llvm/Type.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Pass.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/Target/TargetMachine.h"
22 #include "llvm/Support/InstVisitor.h"
23 #include "llvm/Target/MRegisterInfo.h"
26 using namespace MOTy; // Get Use, Def, UseAndDef
29 struct ISel : public FunctionPass, InstVisitor<ISel> {
31 MachineFunction *F; // The function we are compiling into
32 MachineBasicBlock *BB; // The current MBB we are compiling
35 std::map<Value*, unsigned> RegMap; // Mapping between Val's and SSA Regs
37 ISel(TargetMachine &tm)
38 : TM(tm), F(0), BB(0), CurReg(MRegisterInfo::FirstVirtualRegister) {}
40 /// runOnFunction - Top level implementation of instruction selection for
41 /// the entire function.
43 bool runOnFunction(Function &Fn) {
44 F = &MachineFunction::construct(&Fn, TM);
47 CurReg = MRegisterInfo::FirstVirtualRegister;
49 return false; // We never modify the LLVM itself.
52 /// visitBasicBlock - This method is called when we are visiting a new basic
53 /// block. This simply creates a new MachineBasicBlock to emit code into
54 /// and adds it to the current MachineFunction. Subsequent visit* for
55 /// instructions will be invoked for all instructions in the basic block.
57 void visitBasicBlock(BasicBlock &LLVM_BB) {
58 BB = new MachineBasicBlock(&LLVM_BB);
59 // FIXME: Use the auto-insert form when it's available
60 F->getBasicBlockList().push_back(BB);
63 // Visitation methods for various instructions. These methods simply emit
64 // fixed X86 code for each instruction.
67 // Control flow operators
68 void visitReturnInst(ReturnInst &RI);
69 void visitBranchInst(BranchInst &BI);
70 void visitCallInst(CallInst &I);
72 // Arithmetic operators
73 void visitSimpleBinary(BinaryOperator &B, unsigned OpcodeClass);
74 void visitAdd(BinaryOperator &B) { visitSimpleBinary(B, 0); }
75 void visitSub(BinaryOperator &B) { visitSimpleBinary(B, 1); }
76 void visitMul(BinaryOperator &B);
78 void visitDiv(BinaryOperator &B) { visitDivRem(B); }
79 void visitRem(BinaryOperator &B) { visitDivRem(B); }
80 void visitDivRem(BinaryOperator &B);
83 void visitAnd(BinaryOperator &B) { visitSimpleBinary(B, 2); }
84 void visitOr (BinaryOperator &B) { visitSimpleBinary(B, 3); }
85 void visitXor(BinaryOperator &B) { visitSimpleBinary(B, 4); }
87 // Binary comparison operators
88 void visitSetCCInst(SetCondInst &I, unsigned OpNum);
89 void visitSetEQ(SetCondInst &I) { visitSetCCInst(I, 0); }
90 void visitSetNE(SetCondInst &I) { visitSetCCInst(I, 1); }
91 void visitSetLT(SetCondInst &I) { visitSetCCInst(I, 2); }
92 void visitSetGT(SetCondInst &I) { visitSetCCInst(I, 3); }
93 void visitSetLE(SetCondInst &I) { visitSetCCInst(I, 4); }
94 void visitSetGE(SetCondInst &I) { visitSetCCInst(I, 5); }
96 // Memory Instructions
97 void visitLoadInst(LoadInst &I);
98 void visitStoreInst(StoreInst &I);
101 void visitShiftInst(ShiftInst &I);
102 void visitPHINode(PHINode &I);
103 void visitCastInst(CastInst &I);
105 void visitInstruction(Instruction &I) {
106 std::cerr << "Cannot instruction select: " << I;
110 void promote32 (const unsigned targetReg, Value *v);
112 /// copyConstantToRegister - Output the instructions required to put the
113 /// specified constant into the specified register.
115 void copyConstantToRegister(Constant *C, unsigned Reg);
117 /// getReg - This method turns an LLVM value into a register number. This
118 /// is guaranteed to produce the same register number for a particular value
119 /// every time it is queried.
121 unsigned getReg(Value &V) { return getReg(&V); } // Allow references
122 unsigned getReg(Value *V) {
123 unsigned &Reg = RegMap[V];
128 // Add the mapping of regnumber => reg class to MachineFunction
130 TM.getRegisterInfo()->getRegClassForType(V->getType()));
133 // If this operand is a constant, emit the code to copy the constant into
134 // the register here...
136 if (Constant *C = dyn_cast<Constant>(V)) {
137 copyConstantToRegister(C, Reg);
138 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
139 // Move the address of the global into the register
140 BuildMI(BB, X86::MOVir32, 1, Reg).addReg(GV);
141 } else if (Argument *A = dyn_cast<Argument>(V)) {
142 std::cerr << "ERROR: Arguments not implemented in SimpleInstSel\n";
144 assert(0 && "Don't know how to handle a value of this type!");
152 /// TypeClass - Used by the X86 backend to group LLVM types by their basic X86
156 cByte, cShort, cInt, cLong, cFloat, cDouble
159 /// getClass - Turn a primitive type into a "class" number which is based on the
160 /// size of the type, and whether or not it is floating point.
162 static inline TypeClass getClass(const Type *Ty) {
163 switch (Ty->getPrimitiveID()) {
164 case Type::SByteTyID:
165 case Type::UByteTyID: return cByte; // Byte operands are class #0
166 case Type::ShortTyID:
167 case Type::UShortTyID: return cShort; // Short operands are class #1
170 case Type::PointerTyID: return cInt; // Int's and pointers are class #2
173 case Type::ULongTyID: return cLong; // Longs are class #3
174 case Type::FloatTyID: return cFloat; // Float is class #4
175 case Type::DoubleTyID: return cDouble; // Doubles are class #5
177 assert(0 && "Invalid type to getClass!");
178 return cByte; // not reached
183 /// copyConstantToRegister - Output the instructions required to put the
184 /// specified constant into the specified register.
186 void ISel::copyConstantToRegister(Constant *C, unsigned R) {
187 assert (!isa<ConstantExpr>(C) && "Constant expressions not yet handled!\n");
189 if (C->getType()->isIntegral()) {
190 unsigned Class = getClass(C->getType());
191 assert(Class != 3 && "Type not handled yet!");
193 static const unsigned IntegralOpcodeTab[] = {
194 X86::MOVir8, X86::MOVir16, X86::MOVir32
197 if (C->getType()->isSigned()) {
198 ConstantSInt *CSI = cast<ConstantSInt>(C);
199 BuildMI(BB, IntegralOpcodeTab[Class], 1, R).addSImm(CSI->getValue());
201 ConstantUInt *CUI = cast<ConstantUInt>(C);
202 BuildMI(BB, IntegralOpcodeTab[Class], 1, R).addZImm(CUI->getValue());
205 assert(0 && "Type not handled yet!");
210 /// SetCC instructions - Here we just emit boilerplate code to set a byte-sized
211 /// register, then move it to wherever the result should be.
212 /// We handle FP setcc instructions by pushing them, doing a
213 /// compare-and-pop-twice, and then copying the concodes to the main
214 /// processor's concodes (I didn't make this up, it's in the Intel manual)
216 void ISel::visitSetCCInst(SetCondInst &I, unsigned OpNum) {
217 // The arguments are already supposed to be of the same type.
218 const Type *CompTy = I.getOperand(0)->getType();
219 unsigned reg1 = getReg(I.getOperand(0));
220 unsigned reg2 = getReg(I.getOperand(1));
222 unsigned Class = getClass(CompTy);
224 // Emit: cmp <var1>, <var2> (do the comparison). We can
225 // compare 8-bit with 8-bit, 16-bit with 16-bit, 32-bit with
228 BuildMI (BB, X86::CMPrr8, 2).addReg (reg1).addReg (reg2);
231 BuildMI (BB, X86::CMPrr16, 2).addReg (reg1).addReg (reg2);
234 BuildMI (BB, X86::CMPrr32, 2).addReg (reg1).addReg (reg2);
237 // Push the variables on the stack with fldl opcodes.
238 // FIXME: assuming var1, var2 are in memory, if not, spill to
240 case cFloat: // Floats
241 BuildMI (BB, X86::FLDr4, 1).addReg (reg1);
242 BuildMI (BB, X86::FLDr4, 1).addReg (reg2);
244 case cDouble: // Doubles
245 BuildMI (BB, X86::FLDr8, 1).addReg (reg1);
246 BuildMI (BB, X86::FLDr8, 1).addReg (reg2);
253 if (CompTy->isFloatingPoint()) {
254 // (Non-trapping) compare and pop twice.
255 BuildMI (BB, X86::FUCOMPP, 0);
256 // Move fp status word (concodes) to ax.
257 BuildMI (BB, X86::FNSTSWr8, 1, X86::AX);
258 // Load real concodes from ax.
259 BuildMI (BB, X86::SAHF, 1).addReg(X86::AH);
262 // Emit setOp instruction (extract concode; clobbers ax),
263 // using the following mapping:
264 // LLVM -> X86 signed X86 unsigned
266 // seteq -> sete sete
267 // setne -> setne setne
268 // setlt -> setl setb
269 // setgt -> setg seta
270 // setle -> setle setbe
271 // setge -> setge setae
273 static const unsigned OpcodeTab[2][6] = {
274 {X86::SETEr, X86::SETNEr, X86::SETBr, X86::SETAr, X86::SETBEr, X86::SETAEr},
275 {X86::SETEr, X86::SETNEr, X86::SETLr, X86::SETGr, X86::SETLEr, X86::SETGEr},
278 BuildMI(BB, OpcodeTab[CompTy->isSigned()][OpNum], 0, X86::AL);
280 // Put it in the result using a move.
281 BuildMI (BB, X86::MOVrr8, 1, getReg(I)).addReg(X86::AL);
284 /// promote32 - Emit instructions to turn a narrow operand into a 32-bit-wide
285 /// operand, in the specified target register.
287 ISel::promote32 (const unsigned targetReg, Value *v)
289 unsigned vReg = getReg (v);
290 unsigned Class = getClass (v->getType ());
291 bool isUnsigned = v->getType ()->isUnsigned ();
292 assert (((Class == cByte) || (Class == cShort) || (Class == cInt))
293 && "Unpromotable operand class in promote32");
297 // Extend value into target register (8->32)
299 BuildMI (BB, X86::MOVZXr32r8, 1, targetReg).addReg (vReg);
301 BuildMI (BB, X86::MOVSXr32r8, 1, targetReg).addReg (vReg);
304 // Extend value into target register (16->32)
306 BuildMI (BB, X86::MOVZXr32r16, 1, targetReg).addReg (vReg);
308 BuildMI (BB, X86::MOVSXr32r16, 1, targetReg).addReg (vReg);
311 // Move value into target register (32->32)
312 BuildMI (BB, X86::MOVrr32, 1, targetReg).addReg (vReg);
317 /// 'ret' instruction - Here we are interested in meeting the x86 ABI. As such,
318 /// we have the following possibilities:
320 /// ret void: No return value, simply emit a 'ret' instruction
321 /// ret sbyte, ubyte : Extend value into EAX and return
322 /// ret short, ushort: Extend value into EAX and return
323 /// ret int, uint : Move value into EAX and return
324 /// ret pointer : Move value into EAX and return
325 /// ret long, ulong : Move value into EAX/EDX and return
326 /// ret float/double : Top of FP stack
329 ISel::visitReturnInst (ReturnInst &I)
331 if (I.getNumOperands () == 0)
333 // Emit a 'ret' instruction
334 BuildMI (BB, X86::RET, 0);
337 Value *rv = I.getOperand (0);
338 unsigned Class = getClass (rv->getType ());
341 // integral return values: extend or move into EAX and return.
345 promote32 (X86::EAX, rv);
347 // ret float/double: top of FP stack
349 case cFloat: // Floats
350 BuildMI (BB, X86::FLDr4, 1).addReg (getReg (rv));
352 case cDouble: // Doubles
353 BuildMI (BB, X86::FLDr8, 1).addReg (getReg (rv));
356 // ret long: use EAX(least significant 32 bits)/EDX (most
357 // significant 32)...uh, I think so Brain, but how do i call
358 // up the two parts of the value from inside this mouse
361 visitInstruction (I);
363 // Emit a 'ret' instruction
364 BuildMI (BB, X86::RET, 0);
367 /// visitBranchInst - Handle conditional and unconditional branches here. Note
368 /// that since code layout is frozen at this point, that if we are trying to
369 /// jump to a block that is the immediate successor of the current block, we can
370 /// just make a fall-through. (but we don't currently).
373 ISel::visitBranchInst (BranchInst & BI)
375 if (BI.isConditional ())
377 BasicBlock *ifTrue = BI.getSuccessor (0);
378 BasicBlock *ifFalse = BI.getSuccessor (1); // this is really unobvious
380 // simplest thing I can think of: compare condition with zero,
381 // followed by jump-if-equal to ifFalse, and jump-if-nonequal to
383 unsigned int condReg = getReg (BI.getCondition ());
384 BuildMI (BB, X86::CMPri8, 2).addReg (condReg).addZImm (0);
385 BuildMI (BB, X86::JNE, 1).addPCDisp (BI.getSuccessor (0));
386 BuildMI (BB, X86::JE, 1).addPCDisp (BI.getSuccessor (1));
388 else // unconditional branch
390 BuildMI (BB, X86::JMP, 1).addPCDisp (BI.getSuccessor (0));
394 /// visitCallInst - Push args on stack and do a procedure call instruction.
396 ISel::visitCallInst (CallInst & CI)
398 // Push the arguments on the stack in reverse order, as specified by
400 for (unsigned i = CI.getNumOperands()-1; i >= 1; --i)
402 Value *v = CI.getOperand (i);
403 switch (getClass (v->getType ()))
407 // Promote V to 32 bits wide, and move the result into EAX,
409 promote32 (X86::EAX, v);
410 BuildMI (BB, X86::PUSHr32, 1).addReg (X86::EAX);
414 unsigned Reg = getReg(v);
415 BuildMI (BB, X86::PUSHr32, 1).addReg(Reg);
419 // FIXME: long/ulong/double args not handled.
420 visitInstruction (CI);
424 // Emit a CALL instruction with PC-relative displacement.
425 BuildMI (BB, X86::CALLpcrel32, 1).addPCDisp (CI.getCalledValue ());
428 /// visitSimpleBinary - Implement simple binary operators for integral types...
429 /// OperatorClass is one of: 0 for Add, 1 for Sub, 2 for And, 3 for Or,
432 void ISel::visitSimpleBinary(BinaryOperator &B, unsigned OperatorClass) {
433 if (B.getType() == Type::BoolTy) // FIXME: Handle bools for logicals
436 unsigned Class = getClass(B.getType());
437 if (Class > 2) // FIXME: Handle longs
440 static const unsigned OpcodeTab[][4] = {
441 // Arithmetic operators
442 { X86::ADDrr8, X86::ADDrr16, X86::ADDrr32, 0 }, // ADD
443 { X86::SUBrr8, X86::SUBrr16, X86::SUBrr32, 0 }, // SUB
446 { X86::ANDrr8, X86::ANDrr16, X86::ANDrr32, 0 }, // AND
447 { X86:: ORrr8, X86:: ORrr16, X86:: ORrr32, 0 }, // OR
448 { X86::XORrr8, X86::XORrr16, X86::XORrr32, 0 }, // XOR
451 unsigned Opcode = OpcodeTab[OperatorClass][Class];
452 unsigned Op0r = getReg(B.getOperand(0));
453 unsigned Op1r = getReg(B.getOperand(1));
454 BuildMI(BB, Opcode, 2, getReg(B)).addReg(Op0r).addReg(Op1r);
457 /// visitMul - Multiplies are not simple binary operators because they must deal
458 /// with the EAX register explicitly.
460 void ISel::visitMul(BinaryOperator &I) {
461 unsigned Class = getClass(I.getType());
462 if (Class > 2) // FIXME: Handle longs
465 static const unsigned Regs[] ={ X86::AL , X86::AX , X86::EAX };
466 static const unsigned MulOpcode[]={ X86::MULrr8, X86::MULrr16, X86::MULrr32 };
467 static const unsigned MovOpcode[]={ X86::MOVrr8, X86::MOVrr16, X86::MOVrr32 };
469 unsigned Reg = Regs[Class];
470 unsigned Op0Reg = getReg(I.getOperand(0));
471 unsigned Op1Reg = getReg(I.getOperand(1));
473 // Put the first operand into one of the A registers...
474 BuildMI(BB, MovOpcode[Class], 1, Reg).addReg(Op0Reg);
476 // Emit the appropriate multiply instruction...
477 BuildMI(BB, MulOpcode[Class], 1).addReg(Op1Reg);
479 // Put the result into the destination register...
480 BuildMI(BB, MovOpcode[Class], 1, getReg(I)).addReg(Reg);
484 /// visitDivRem - Handle division and remainder instructions... these
485 /// instruction both require the same instructions to be generated, they just
486 /// select the result from a different register. Note that both of these
487 /// instructions work differently for signed and unsigned operands.
489 void ISel::visitDivRem(BinaryOperator &I) {
490 unsigned Class = getClass(I.getType());
491 if (Class > 2) // FIXME: Handle longs
494 static const unsigned Regs[] ={ X86::AL , X86::AX , X86::EAX };
495 static const unsigned MovOpcode[]={ X86::MOVrr8, X86::MOVrr16, X86::MOVrr32 };
496 static const unsigned ExtOpcode[]={ X86::CBW , X86::CWD , X86::CDQ };
497 static const unsigned ClrOpcode[]={ X86::XORrr8, X86::XORrr16, X86::XORrr32 };
498 static const unsigned ExtRegs[] ={ X86::AH , X86::DX , X86::EDX };
500 static const unsigned DivOpcode[][4] = {
501 { X86::DIVrr8 , X86::DIVrr16 , X86::DIVrr32 , 0 }, // Unsigned division
502 { X86::IDIVrr8, X86::IDIVrr16, X86::IDIVrr32, 0 }, // Signed division
505 bool isSigned = I.getType()->isSigned();
506 unsigned Reg = Regs[Class];
507 unsigned ExtReg = ExtRegs[Class];
508 unsigned Op0Reg = getReg(I.getOperand(0));
509 unsigned Op1Reg = getReg(I.getOperand(1));
511 // Put the first operand into one of the A registers...
512 BuildMI(BB, MovOpcode[Class], 1, Reg).addReg(Op0Reg);
515 // Emit a sign extension instruction...
516 BuildMI(BB, ExtOpcode[Class], 0);
518 // If unsigned, emit a zeroing instruction... (reg = xor reg, reg)
519 BuildMI(BB, ClrOpcode[Class], 2, ExtReg).addReg(ExtReg).addReg(ExtReg);
522 // Emit the appropriate divide or remainder instruction...
523 BuildMI(BB, DivOpcode[isSigned][Class], 1).addReg(Op1Reg);
525 // Figure out which register we want to pick the result out of...
526 unsigned DestReg = (I.getOpcode() == Instruction::Div) ? Reg : ExtReg;
528 // Put the result into the destination register...
529 BuildMI(BB, MovOpcode[Class], 1, getReg(I)).addReg(DestReg);
533 /// Shift instructions: 'shl', 'sar', 'shr' - Some special cases here
534 /// for constant immediate shift values, and for constant immediate
535 /// shift values equal to 1. Even the general case is sort of special,
536 /// because the shift amount has to be in CL, not just any old register.
538 void ISel::visitShiftInst (ShiftInst &I) {
539 unsigned Op0r = getReg (I.getOperand(0));
540 unsigned DestReg = getReg(I);
541 bool isLeftShift = I.getOpcode() == Instruction::Shl;
542 bool isOperandSigned = I.getType()->isUnsigned();
543 unsigned OperandClass = getClass(I.getType());
545 if (OperandClass > 2)
546 visitInstruction(I); // Can't handle longs yet!
548 if (ConstantUInt *CUI = dyn_cast <ConstantUInt> (I.getOperand (1)))
550 // The shift amount is constant, guaranteed to be a ubyte. Get its value.
551 assert(CUI->getType() == Type::UByteTy && "Shift amount not a ubyte?");
552 unsigned char shAmt = CUI->getValue();
554 static const unsigned ConstantOperand[][4] = {
555 { X86::SHRir8, X86::SHRir16, X86::SHRir32, 0 }, // SHR
556 { X86::SARir8, X86::SARir16, X86::SARir32, 0 }, // SAR
557 { X86::SHLir8, X86::SHLir16, X86::SHLir32, 0 }, // SHL
558 { X86::SHLir8, X86::SHLir16, X86::SHLir32, 0 }, // SAL = SHL
561 const unsigned *OpTab = // Figure out the operand table to use
562 ConstantOperand[isLeftShift*2+isOperandSigned];
564 // Emit: <insn> reg, shamt (shift-by-immediate opcode "ir" form.)
565 BuildMI(BB, OpTab[OperandClass], 2, DestReg).addReg(Op0r).addZImm(shAmt);
569 // The shift amount is non-constant.
571 // In fact, you can only shift with a variable shift amount if
572 // that amount is already in the CL register, so we have to put it
576 // Emit: move cl, shiftAmount (put the shift amount in CL.)
577 BuildMI(BB, X86::MOVrr8, 1, X86::CL).addReg(getReg(I.getOperand(1)));
579 // This is a shift right (SHR).
580 static const unsigned NonConstantOperand[][4] = {
581 { X86::SHRrr8, X86::SHRrr16, X86::SHRrr32, 0 }, // SHR
582 { X86::SARrr8, X86::SARrr16, X86::SARrr32, 0 }, // SAR
583 { X86::SHLrr8, X86::SHLrr16, X86::SHLrr32, 0 }, // SHL
584 { X86::SHLrr8, X86::SHLrr16, X86::SHLrr32, 0 }, // SAL = SHL
587 const unsigned *OpTab = // Figure out the operand table to use
588 NonConstantOperand[isLeftShift*2+isOperandSigned];
590 BuildMI(BB, OpTab[OperandClass], 1, DestReg).addReg(Op0r);
595 /// visitLoadInst - Implement LLVM load instructions in terms of the x86 'mov'
598 void ISel::visitLoadInst(LoadInst &I) {
599 unsigned Class = getClass(I.getType());
600 if (Class > 2) // FIXME: Handle longs and others...
603 static const unsigned Opcode[] = { X86::MOVmr8, X86::MOVmr16, X86::MOVmr32 };
605 unsigned AddressReg = getReg(I.getOperand(0));
606 addDirectMem(BuildMI(BB, Opcode[Class], 4, getReg(I)), AddressReg);
610 /// visitStoreInst - Implement LLVM store instructions in terms of the x86 'mov'
613 void ISel::visitStoreInst(StoreInst &I) {
614 unsigned Class = getClass(I.getOperand(0)->getType());
615 if (Class > 2) // FIXME: Handle longs and others...
618 static const unsigned Opcode[] = { X86::MOVrm8, X86::MOVrm16, X86::MOVrm32 };
620 unsigned ValReg = getReg(I.getOperand(0));
621 unsigned AddressReg = getReg(I.getOperand(1));
622 addDirectMem(BuildMI(BB, Opcode[Class], 1+4), AddressReg).addReg(ValReg);
626 /// visitPHINode - Turn an LLVM PHI node into an X86 PHI node...
628 void ISel::visitPHINode(PHINode &PN) {
629 MachineInstr *MI = BuildMI(BB, X86::PHI, PN.getNumOperands(), getReg(PN));
631 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
632 // FIXME: This will put constants after the PHI nodes in the block, which
633 // is invalid. They should be put inline into the PHI node eventually.
635 MI->addRegOperand(getReg(PN.getIncomingValue(i)));
636 MI->addPCDispOperand(PN.getIncomingBlock(i));
640 /// visitCastInst - Here we have various kinds of copying with or without
641 /// sign extension going on.
643 ISel::visitCastInst (CastInst &CI)
645 //> cast larger int to smaller int --> copy least significant byte/word w/ mov?
647 //I'm not really sure what to do with this. We could insert a pseudo-op
648 //that says take the low X bits of a Y bit register, but for now we can just
649 //force the value into, say, EAX, then rip out AL or AX. The advantage of
650 //the former is that the register allocator could use any register it wants,
651 //but for now this obviously doesn't matter. :)
653 const Type *targetType = CI.getType ();
654 Value *operand = CI.getOperand (0);
655 unsigned int operandReg = getReg (operand);
656 const Type *sourceType = operand->getType ();
657 unsigned int destReg = getReg (CI);
660 if (targetType == Type::BoolTy) {
662 BuildMI (BB, X86::CMPri8, 2).addReg (operandReg).addZImm (0);
663 // Emit Set-if-not-zero
664 BuildMI (BB, X86::SETNEr, 1, destReg);
668 // if size of target type == size of source type
669 // Emit Mov reg(target) <- reg(source)
671 // if size of target type > size of source type
672 // if both types are integer types
673 // if source type is signed
674 // sbyte to short, ushort: Emit movsx 8->16
675 // sbyte to int, uint: Emit movsx 8->32
676 // short to int, uint: Emit movsx 16->32
677 // else if source type is unsigned
678 // ubyte to short, ushort: Emit movzx 8->16
679 // ubyte to int, uint: Emit movzx 8->32
680 // ushort to int, uint: Emit movzx 16->32
681 // if both types are fp types
682 // float to double: Emit fstp, fld (???)
684 visitInstruction (CI);
687 /// createSimpleX86InstructionSelector - This pass converts an LLVM function
688 /// into a machine code representation is a very simple peep-hole fashion. The
689 /// generated code sucks but the implementation is nice and simple.
691 Pass *createSimpleX86InstructionSelector(TargetMachine &TM) {