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);
144 /// TypeClass - Used by the X86 backend to group LLVM types by their basic X86
148 cByte, cShort, cInt, cLong, cFloat, cDouble
151 /// getClass - Turn a primitive type into a "class" number which is based on the
152 /// size of the type, and whether or not it is floating point.
154 static inline TypeClass getClass(const Type *Ty) {
155 switch (Ty->getPrimitiveID()) {
156 case Type::SByteTyID:
157 case Type::UByteTyID: return cByte; // Byte operands are class #0
158 case Type::ShortTyID:
159 case Type::UShortTyID: return cShort; // Short operands are class #1
162 case Type::PointerTyID: return cInt; // Int's and pointers are class #2
165 case Type::ULongTyID: return cLong; // Longs are class #3
166 case Type::FloatTyID: return cFloat; // Float is class #4
167 case Type::DoubleTyID: return cDouble; // Doubles are class #5
169 assert(0 && "Invalid type to getClass!");
170 return cByte; // not reached
175 /// copyConstantToRegister - Output the instructions required to put the
176 /// specified constant into the specified register.
178 void ISel::copyConstantToRegister(Constant *C, unsigned R) {
179 assert (!isa<ConstantExpr>(C) && "Constant expressions not yet handled!\n");
181 if (C->getType()->isIntegral()) {
182 unsigned Class = getClass(C->getType());
183 assert(Class != 3 && "Type not handled yet!");
185 static const unsigned IntegralOpcodeTab[] = {
186 X86::MOVir8, X86::MOVir16, X86::MOVir32
189 if (C->getType()->isSigned()) {
190 ConstantSInt *CSI = cast<ConstantSInt>(C);
191 BuildMI(BB, IntegralOpcodeTab[Class], 1, R).addSImm(CSI->getValue());
193 ConstantUInt *CUI = cast<ConstantUInt>(C);
194 BuildMI(BB, IntegralOpcodeTab[Class], 1, R).addZImm(CUI->getValue());
197 assert(0 && "Type not handled yet!");
202 /// SetCC instructions - Here we just emit boilerplate code to set a byte-sized
203 /// register, then move it to wherever the result should be.
204 /// We handle FP setcc instructions by pushing them, doing a
205 /// compare-and-pop-twice, and then copying the concodes to the main
206 /// processor's concodes (I didn't make this up, it's in the Intel manual)
208 void ISel::visitSetCCInst(SetCondInst &I, unsigned OpNum) {
209 // The arguments are already supposed to be of the same type.
210 const Type *CompTy = I.getOperand(0)->getType();
211 unsigned reg1 = getReg(I.getOperand(0));
212 unsigned reg2 = getReg(I.getOperand(1));
214 unsigned Class = getClass(CompTy);
216 // Emit: cmp <var1>, <var2> (do the comparison). We can
217 // compare 8-bit with 8-bit, 16-bit with 16-bit, 32-bit with
220 BuildMI (BB, X86::CMPrr8, 2).addReg (reg1).addReg (reg2);
223 BuildMI (BB, X86::CMPrr16, 2).addReg (reg1).addReg (reg2);
226 BuildMI (BB, X86::CMPrr32, 2).addReg (reg1).addReg (reg2);
229 // Push the variables on the stack with fldl opcodes.
230 // FIXME: assuming var1, var2 are in memory, if not, spill to
232 case cFloat: // Floats
233 BuildMI (BB, X86::FLDr4, 1).addReg (reg1);
234 BuildMI (BB, X86::FLDr4, 1).addReg (reg2);
236 case cDouble: // Doubles
237 BuildMI (BB, X86::FLDr8, 1).addReg (reg1);
238 BuildMI (BB, X86::FLDr8, 1).addReg (reg2);
245 if (CompTy->isFloatingPoint()) {
246 // (Non-trapping) compare and pop twice.
247 BuildMI (BB, X86::FUCOMPP, 0);
248 // Move fp status word (concodes) to ax.
249 BuildMI (BB, X86::FNSTSWr8, 1, X86::AX);
250 // Load real concodes from ax.
251 BuildMI (BB, X86::SAHF, 1).addReg(X86::AH);
254 // Emit setOp instruction (extract concode; clobbers ax),
255 // using the following mapping:
256 // LLVM -> X86 signed X86 unsigned
258 // seteq -> sete sete
259 // setne -> setne setne
260 // setlt -> setl setb
261 // setgt -> setg seta
262 // setle -> setle setbe
263 // setge -> setge setae
265 static const unsigned OpcodeTab[2][6] = {
266 {X86::SETEr, X86::SETNEr, X86::SETBr, X86::SETAr, X86::SETBEr, X86::SETAEr},
267 {X86::SETEr, X86::SETNEr, X86::SETLr, X86::SETGr, X86::SETLEr, X86::SETGEr},
270 BuildMI(BB, OpcodeTab[CompTy->isSigned()][OpNum], 0, X86::AL);
272 // Put it in the result using a move.
273 BuildMI (BB, X86::MOVrr8, 1, getReg(I)).addReg(X86::AL);
276 /// promote32 - Emit instructions to turn a narrow operand into a 32-bit-wide
277 /// operand, in the specified target register.
279 ISel::promote32 (const unsigned targetReg, Value *v)
281 unsigned vReg = getReg (v);
282 unsigned Class = getClass (v->getType ());
283 bool isUnsigned = v->getType ()->isUnsigned ();
284 assert (((Class == cByte) || (Class == cShort) || (Class == cInt))
285 && "Unpromotable operand class in promote32");
289 // Extend value into target register (8->32)
291 BuildMI (BB, X86::MOVZXr32r8, 1, targetReg).addReg (vReg);
293 BuildMI (BB, X86::MOVSXr32r8, 1, targetReg).addReg (vReg);
296 // Extend value into target register (16->32)
298 BuildMI (BB, X86::MOVZXr32r16, 1, targetReg).addReg (vReg);
300 BuildMI (BB, X86::MOVSXr32r16, 1, targetReg).addReg (vReg);
303 // Move value into target register (32->32)
304 BuildMI (BB, X86::MOVrr32, 1, targetReg).addReg (vReg);
309 /// 'ret' instruction - Here we are interested in meeting the x86 ABI. As such,
310 /// we have the following possibilities:
312 /// ret void: No return value, simply emit a 'ret' instruction
313 /// ret sbyte, ubyte : Extend value into EAX and return
314 /// ret short, ushort: Extend value into EAX and return
315 /// ret int, uint : Move value into EAX and return
316 /// ret pointer : Move value into EAX and return
317 /// ret long, ulong : Move value into EAX/EDX and return
318 /// ret float/double : Top of FP stack
321 ISel::visitReturnInst (ReturnInst &I)
323 if (I.getNumOperands () == 0)
325 // Emit a 'ret' instruction
326 BuildMI (BB, X86::RET, 0);
329 Value *rv = I.getOperand (0);
330 unsigned Class = getClass (rv->getType ());
333 // integral return values: extend or move into EAX and return.
337 promote32 (X86::EAX, rv);
339 // ret float/double: top of FP stack
341 case cFloat: // Floats
342 BuildMI (BB, X86::FLDr4, 1).addReg (getReg (rv));
344 case cDouble: // Doubles
345 BuildMI (BB, X86::FLDr8, 1).addReg (getReg (rv));
348 // ret long: use EAX(least significant 32 bits)/EDX (most
349 // significant 32)...uh, I think so Brain, but how do i call
350 // up the two parts of the value from inside this mouse
353 visitInstruction (I);
355 // Emit a 'ret' instruction
356 BuildMI (BB, X86::RET, 0);
359 /// visitBranchInst - Handle conditional and unconditional branches here. Note
360 /// that since code layout is frozen at this point, that if we are trying to
361 /// jump to a block that is the immediate successor of the current block, we can
362 /// just make a fall-through. (but we don't currently).
365 ISel::visitBranchInst (BranchInst & BI)
367 if (BI.isConditional ())
369 BasicBlock *ifTrue = BI.getSuccessor (0);
370 BasicBlock *ifFalse = BI.getSuccessor (1); // this is really unobvious
372 // simplest thing I can think of: compare condition with zero,
373 // followed by jump-if-equal to ifFalse, and jump-if-nonequal to
375 unsigned int condReg = getReg (BI.getCondition ());
376 BuildMI (BB, X86::CMPri8, 2).addReg (condReg).addZImm (0);
377 BuildMI (BB, X86::JNE, 1).addPCDisp (BI.getSuccessor (0));
378 BuildMI (BB, X86::JE, 1).addPCDisp (BI.getSuccessor (1));
380 else // unconditional branch
382 BuildMI (BB, X86::JMP, 1).addPCDisp (BI.getSuccessor (0));
386 /// visitCallInst - Push args on stack and do a procedure call instruction.
388 ISel::visitCallInst (CallInst & CI)
390 // Push the arguments on the stack in reverse order, as specified by
392 for (unsigned i = CI.getNumOperands (); i >= 1; --i)
394 Value *v = CI.getOperand (i);
395 unsigned argReg = getReg (v);
396 switch (getClass (v->getType ()))
400 promote32 (X86::EAX, v);
401 BuildMI (BB, X86::PUSHr32, 1).addReg (X86::EAX);
405 BuildMI (BB, X86::PUSHr32, 1).addReg (argReg);
409 visitInstruction (CI);
413 // Emit a CALL instruction with PC-relative displacement.
414 BuildMI (BB, X86::CALLpcrel32, 1).addPCDisp (CI.getCalledValue ());
417 /// visitSimpleBinary - Implement simple binary operators for integral types...
418 /// OperatorClass is one of: 0 for Add, 1 for Sub, 2 for And, 3 for Or,
421 void ISel::visitSimpleBinary(BinaryOperator &B, unsigned OperatorClass) {
422 if (B.getType() == Type::BoolTy) // FIXME: Handle bools for logicals
425 unsigned Class = getClass(B.getType());
426 if (Class > 2) // FIXME: Handle longs
429 static const unsigned OpcodeTab[][4] = {
430 // Arithmetic operators
431 { X86::ADDrr8, X86::ADDrr16, X86::ADDrr32, 0 }, // ADD
432 { X86::SUBrr8, X86::SUBrr16, X86::SUBrr32, 0 }, // SUB
435 { X86::ANDrr8, X86::ANDrr16, X86::ANDrr32, 0 }, // AND
436 { X86:: ORrr8, X86:: ORrr16, X86:: ORrr32, 0 }, // OR
437 { X86::XORrr8, X86::XORrr16, X86::XORrr32, 0 }, // XOR
440 unsigned Opcode = OpcodeTab[OperatorClass][Class];
441 unsigned Op0r = getReg(B.getOperand(0));
442 unsigned Op1r = getReg(B.getOperand(1));
443 BuildMI(BB, Opcode, 2, getReg(B)).addReg(Op0r).addReg(Op1r);
446 /// visitMul - Multiplies are not simple binary operators because they must deal
447 /// with the EAX register explicitly.
449 void ISel::visitMul(BinaryOperator &I) {
450 unsigned Class = getClass(I.getType());
451 if (Class > 2) // FIXME: Handle longs
454 static const unsigned Regs[] ={ X86::AL , X86::AX , X86::EAX };
455 static const unsigned MulOpcode[]={ X86::MULrr8, X86::MULrr16, X86::MULrr32 };
456 static const unsigned MovOpcode[]={ X86::MOVrr8, X86::MOVrr16, X86::MOVrr32 };
458 unsigned Reg = Regs[Class];
459 unsigned Op0Reg = getReg(I.getOperand(0));
460 unsigned Op1Reg = getReg(I.getOperand(1));
462 // Put the first operand into one of the A registers...
463 BuildMI(BB, MovOpcode[Class], 1, Reg).addReg(Op0Reg);
465 // Emit the appropriate multiply instruction...
466 BuildMI(BB, MulOpcode[Class], 1).addReg(Op1Reg);
468 // Put the result into the destination register...
469 BuildMI(BB, MovOpcode[Class], 1, getReg(I)).addReg(Reg);
473 /// visitDivRem - Handle division and remainder instructions... these
474 /// instruction both require the same instructions to be generated, they just
475 /// select the result from a different register. Note that both of these
476 /// instructions work differently for signed and unsigned operands.
478 void ISel::visitDivRem(BinaryOperator &I) {
479 unsigned Class = getClass(I.getType());
480 if (Class > 2) // FIXME: Handle longs
483 static const unsigned Regs[] ={ X86::AL , X86::AX , X86::EAX };
484 static const unsigned MovOpcode[]={ X86::MOVrr8, X86::MOVrr16, X86::MOVrr32 };
485 static const unsigned ExtOpcode[]={ X86::CBW , X86::CWD , X86::CDQ };
486 static const unsigned ClrOpcode[]={ X86::XORrr8, X86::XORrr16, X86::XORrr32 };
487 static const unsigned ExtRegs[] ={ X86::AH , X86::DX , X86::EDX };
489 static const unsigned DivOpcode[][4] = {
490 { X86::DIVrr8 , X86::DIVrr16 , X86::DIVrr32 , 0 }, // Unsigned division
491 { X86::IDIVrr8, X86::IDIVrr16, X86::IDIVrr32, 0 }, // Signed division
494 bool isSigned = I.getType()->isSigned();
495 unsigned Reg = Regs[Class];
496 unsigned ExtReg = ExtRegs[Class];
497 unsigned Op0Reg = getReg(I.getOperand(0));
498 unsigned Op1Reg = getReg(I.getOperand(1));
500 // Put the first operand into one of the A registers...
501 BuildMI(BB, MovOpcode[Class], 1, Reg).addReg(Op0Reg);
504 // Emit a sign extension instruction...
505 BuildMI(BB, ExtOpcode[Class], 1, ExtReg).addReg(Reg);
507 // If unsigned, emit a zeroing instruction... (reg = xor reg, reg)
508 BuildMI(BB, ClrOpcode[Class], 2, ExtReg).addReg(ExtReg).addReg(ExtReg);
511 // Emit the appropriate divide or remainder instruction...
512 BuildMI(BB, DivOpcode[isSigned][Class], 1).addReg(Op1Reg);
514 // Figure out which register we want to pick the result out of...
515 unsigned DestReg = (I.getOpcode() == Instruction::Div) ? Reg : ExtReg;
517 // Put the result into the destination register...
518 BuildMI(BB, MovOpcode[Class], 1, getReg(I)).addReg(DestReg);
522 /// Shift instructions: 'shl', 'sar', 'shr' - Some special cases here
523 /// for constant immediate shift values, and for constant immediate
524 /// shift values equal to 1. Even the general case is sort of special,
525 /// because the shift amount has to be in CL, not just any old register.
527 void ISel::visitShiftInst (ShiftInst &I) {
528 unsigned Op0r = getReg (I.getOperand(0));
529 unsigned DestReg = getReg(I);
530 bool isLeftShift = I.getOpcode() == Instruction::Shl;
531 bool isOperandSigned = I.getType()->isUnsigned();
532 unsigned OperandClass = getClass(I.getType());
534 if (OperandClass > 2)
535 visitInstruction(I); // Can't handle longs yet!
537 if (ConstantUInt *CUI = dyn_cast <ConstantUInt> (I.getOperand (1)))
539 // The shift amount is constant, guaranteed to be a ubyte. Get its value.
540 assert(CUI->getType() == Type::UByteTy && "Shift amount not a ubyte?");
541 unsigned char shAmt = CUI->getValue();
543 static const unsigned ConstantOperand[][4] = {
544 { X86::SHRir8, X86::SHRir16, X86::SHRir32, 0 }, // SHR
545 { X86::SARir8, X86::SARir16, X86::SARir32, 0 }, // SAR
546 { X86::SHLir8, X86::SHLir16, X86::SHLir32, 0 }, // SHL
547 { X86::SHLir8, X86::SHLir16, X86::SHLir32, 0 }, // SAL = SHL
550 const unsigned *OpTab = // Figure out the operand table to use
551 ConstantOperand[isLeftShift*2+isOperandSigned];
553 // Emit: <insn> reg, shamt (shift-by-immediate opcode "ir" form.)
554 BuildMI(BB, OpTab[OperandClass], 2, DestReg).addReg(Op0r).addZImm(shAmt);
558 // The shift amount is non-constant.
560 // In fact, you can only shift with a variable shift amount if
561 // that amount is already in the CL register, so we have to put it
565 // Emit: move cl, shiftAmount (put the shift amount in CL.)
566 BuildMI(BB, X86::MOVrr8, 1, X86::CL).addReg(getReg(I.getOperand(1)));
568 // This is a shift right (SHR).
569 static const unsigned NonConstantOperand[][4] = {
570 { X86::SHRrr8, X86::SHRrr16, X86::SHRrr32, 0 }, // SHR
571 { X86::SARrr8, X86::SARrr16, X86::SARrr32, 0 }, // SAR
572 { X86::SHLrr8, X86::SHLrr16, X86::SHLrr32, 0 }, // SHL
573 { X86::SHLrr8, X86::SHLrr16, X86::SHLrr32, 0 }, // SAL = SHL
576 const unsigned *OpTab = // Figure out the operand table to use
577 NonConstantOperand[isLeftShift*2+isOperandSigned];
579 BuildMI(BB, OpTab[OperandClass], 1, DestReg).addReg(Op0r);
584 /// visitLoadInst - Implement LLVM load instructions in terms of the x86 'mov'
587 void ISel::visitLoadInst(LoadInst &I) {
588 unsigned Class = getClass(I.getType());
589 if (Class > 2) // FIXME: Handle longs and others...
592 static const unsigned Opcode[] = { X86::MOVmr8, X86::MOVmr16, X86::MOVmr32 };
594 unsigned AddressReg = getReg(I.getOperand(0));
595 addDirectMem(BuildMI(BB, Opcode[Class], 4, getReg(I)), AddressReg);
599 /// visitStoreInst - Implement LLVM store instructions in terms of the x86 'mov'
602 void ISel::visitStoreInst(StoreInst &I) {
603 unsigned Class = getClass(I.getOperand(0)->getType());
604 if (Class > 2) // FIXME: Handle longs and others...
607 static const unsigned Opcode[] = { X86::MOVrm8, X86::MOVrm16, X86::MOVrm32 };
609 unsigned ValReg = getReg(I.getOperand(0));
610 unsigned AddressReg = getReg(I.getOperand(1));
611 addDirectMem(BuildMI(BB, Opcode[Class], 1+4), AddressReg).addReg(ValReg);
615 /// visitPHINode - Turn an LLVM PHI node into an X86 PHI node...
617 void ISel::visitPHINode(PHINode &PN) {
618 MachineInstr *MI = BuildMI(BB, X86::PHI, PN.getNumOperands(), getReg(PN));
620 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
621 // FIXME: This will put constants after the PHI nodes in the block, which
622 // is invalid. They should be put inline into the PHI node eventually.
624 MI->addRegOperand(getReg(PN.getIncomingValue(i)));
625 MI->addPCDispOperand(PN.getIncomingBlock(i));
629 /// visitCastInst - Here we have various kinds of copying with or without
630 /// sign extension going on.
632 ISel::visitCastInst (CastInst &CI)
634 //> cast larger int to smaller int --> copy least significant byte/word w/ mov?
636 //I'm not really sure what to do with this. We could insert a pseudo-op
637 //that says take the low X bits of a Y bit register, but for now we can just
638 //force the value into, say, EAX, then rip out AL or AX. The advantage of
639 //the former is that the register allocator could use any register it wants,
640 //but for now this obviously doesn't matter. :)
642 // if target type is bool
644 // Emit Set-if-not-zero
646 // if size of target type == size of source type
647 // Emit Mov reg(target) <- reg(source)
649 // if size of target type > size of source type
650 // if both types are integer types
651 // if source type is signed
652 // sbyte to short, ushort: Emit movsx 8->16
653 // sbyte to int, uint: Emit movsx 8->32
654 // short to int, uint: Emit movsx 16->32
655 // else if source type is unsigned
656 // ubyte to short, ushort: Emit movzx 8->16
657 // ubyte to int, uint: Emit movzx 8->32
658 // ushort to int, uint: Emit movzx 16->32
659 // if both types are fp types
660 // float to double: Emit fstp, fld (???)
662 visitInstruction (CI);
665 /// createSimpleX86InstructionSelector - This pass converts an LLVM function
666 /// into a machine code representation is a very simple peep-hole fashion. The
667 /// generated code sucks but the implementation is nice and simple.
669 Pass *createSimpleX86InstructionSelector(TargetMachine &TM) {