1 //===-- X86ATTInstPrinter.cpp - AT&T assembly instruction printing --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file includes code for rendering MCInst instances as AT&T-style
10 // assembly.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "X86ATTInstPrinter.h"
15 #include "X86BaseInfo.h"
16 #include "X86InstComments.h"
17 #include "llvm/MC/MCExpr.h"
18 #include "llvm/MC/MCInst.h"
19 #include "llvm/MC/MCInstrInfo.h"
20 #include "llvm/MC/MCSubtargetInfo.h"
21 #include "llvm/Support/Casting.h"
22 #include "llvm/Support/ErrorHandling.h"
23 #include "llvm/Support/Format.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include <cassert>
26 #include <cinttypes>
27 #include <cstdint>
28
29 using namespace llvm;
30
31 #define DEBUG_TYPE "asm-printer"
32
33 // Include the auto-generated portion of the assembly writer.
34 #define PRINT_ALIAS_INSTR
35 #include "X86GenAsmWriter.inc"
36
printRegName(raw_ostream & OS,unsigned RegNo) const37 void X86ATTInstPrinter::printRegName(raw_ostream &OS, unsigned RegNo) const {
38 OS << markup("<reg:") << '%' << getRegisterName(RegNo) << markup(">");
39 }
40
printInst(const MCInst * MI,uint64_t Address,StringRef Annot,const MCSubtargetInfo & STI,raw_ostream & OS)41 void X86ATTInstPrinter::printInst(const MCInst *MI, uint64_t Address,
42 StringRef Annot, const MCSubtargetInfo &STI,
43 raw_ostream &OS) {
44 // If verbose assembly is enabled, we can print some informative comments.
45 if (CommentStream)
46 HasCustomInstComment = EmitAnyX86InstComments(MI, *CommentStream, MII);
47
48 printInstFlags(MI, OS);
49
50 // Output CALLpcrel32 as "callq" in 64-bit mode.
51 // In Intel annotation it's always emitted as "call".
52 //
53 // TODO: Probably this hack should be redesigned via InstAlias in
54 // InstrInfo.td as soon as Requires clause is supported properly
55 // for InstAlias.
56 if (MI->getOpcode() == X86::CALLpcrel32 &&
57 (STI.getFeatureBits()[X86::Mode64Bit])) {
58 OS << "\tcallq\t";
59 printPCRelImm(MI, 0, OS);
60 }
61 // data16 and data32 both have the same encoding of 0x66. While data32 is
62 // valid only in 16 bit systems, data16 is valid in the rest.
63 // There seems to be some lack of support of the Requires clause that causes
64 // 0x66 to be interpreted as "data16" by the asm printer.
65 // Thus we add an adjustment here in order to print the "right" instruction.
66 else if (MI->getOpcode() == X86::DATA16_PREFIX &&
67 STI.getFeatureBits()[X86::Mode16Bit]) {
68 OS << "\tdata32";
69 }
70 // Try to print any aliases first.
71 else if (!printAliasInstr(MI, OS) &&
72 !printVecCompareInstr(MI, OS))
73 printInstruction(MI, Address, OS);
74
75 // Next always print the annotation.
76 printAnnotation(OS, Annot);
77 }
78
printVecCompareInstr(const MCInst * MI,raw_ostream & OS)79 bool X86ATTInstPrinter::printVecCompareInstr(const MCInst *MI,
80 raw_ostream &OS) {
81 if (MI->getNumOperands() == 0 ||
82 !MI->getOperand(MI->getNumOperands() - 1).isImm())
83 return false;
84
85 int64_t Imm = MI->getOperand(MI->getNumOperands() - 1).getImm();
86
87 const MCInstrDesc &Desc = MII.get(MI->getOpcode());
88
89 // Custom print the vector compare instructions to get the immediate
90 // translated into the mnemonic.
91 switch (MI->getOpcode()) {
92 case X86::CMPPDrmi: case X86::CMPPDrri:
93 case X86::CMPPSrmi: case X86::CMPPSrri:
94 case X86::CMPSDrm: case X86::CMPSDrr:
95 case X86::CMPSDrm_Int: case X86::CMPSDrr_Int:
96 case X86::CMPSSrm: case X86::CMPSSrr:
97 case X86::CMPSSrm_Int: case X86::CMPSSrr_Int:
98 if (Imm >= 0 && Imm <= 7) {
99 OS << '\t';
100 printCMPMnemonic(MI, /*IsVCMP*/false, OS);
101
102 if ((Desc.TSFlags & X86II::FormMask) == X86II::MRMSrcMem) {
103 if ((Desc.TSFlags & X86II::OpPrefixMask) == X86II::XS)
104 printdwordmem(MI, 2, OS);
105 else if ((Desc.TSFlags & X86II::OpPrefixMask) == X86II::XD)
106 printqwordmem(MI, 2, OS);
107 else
108 printxmmwordmem(MI, 2, OS);
109 } else
110 printOperand(MI, 2, OS);
111
112 // Skip operand 1 as its tied to the dest.
113
114 OS << ", ";
115 printOperand(MI, 0, OS);
116 return true;
117 }
118 break;
119
120 case X86::VCMPPDrmi: case X86::VCMPPDrri:
121 case X86::VCMPPDYrmi: case X86::VCMPPDYrri:
122 case X86::VCMPPDZ128rmi: case X86::VCMPPDZ128rri:
123 case X86::VCMPPDZ256rmi: case X86::VCMPPDZ256rri:
124 case X86::VCMPPDZrmi: case X86::VCMPPDZrri:
125 case X86::VCMPPSrmi: case X86::VCMPPSrri:
126 case X86::VCMPPSYrmi: case X86::VCMPPSYrri:
127 case X86::VCMPPSZ128rmi: case X86::VCMPPSZ128rri:
128 case X86::VCMPPSZ256rmi: case X86::VCMPPSZ256rri:
129 case X86::VCMPPSZrmi: case X86::VCMPPSZrri:
130 case X86::VCMPSDrm: case X86::VCMPSDrr:
131 case X86::VCMPSDZrm: case X86::VCMPSDZrr:
132 case X86::VCMPSDrm_Int: case X86::VCMPSDrr_Int:
133 case X86::VCMPSDZrm_Int: case X86::VCMPSDZrr_Int:
134 case X86::VCMPSSrm: case X86::VCMPSSrr:
135 case X86::VCMPSSZrm: case X86::VCMPSSZrr:
136 case X86::VCMPSSrm_Int: case X86::VCMPSSrr_Int:
137 case X86::VCMPSSZrm_Int: case X86::VCMPSSZrr_Int:
138 case X86::VCMPPDZ128rmik: case X86::VCMPPDZ128rrik:
139 case X86::VCMPPDZ256rmik: case X86::VCMPPDZ256rrik:
140 case X86::VCMPPDZrmik: case X86::VCMPPDZrrik:
141 case X86::VCMPPSZ128rmik: case X86::VCMPPSZ128rrik:
142 case X86::VCMPPSZ256rmik: case X86::VCMPPSZ256rrik:
143 case X86::VCMPPSZrmik: case X86::VCMPPSZrrik:
144 case X86::VCMPSDZrm_Intk: case X86::VCMPSDZrr_Intk:
145 case X86::VCMPSSZrm_Intk: case X86::VCMPSSZrr_Intk:
146 case X86::VCMPPDZ128rmbi: case X86::VCMPPDZ128rmbik:
147 case X86::VCMPPDZ256rmbi: case X86::VCMPPDZ256rmbik:
148 case X86::VCMPPDZrmbi: case X86::VCMPPDZrmbik:
149 case X86::VCMPPSZ128rmbi: case X86::VCMPPSZ128rmbik:
150 case X86::VCMPPSZ256rmbi: case X86::VCMPPSZ256rmbik:
151 case X86::VCMPPSZrmbi: case X86::VCMPPSZrmbik:
152 case X86::VCMPPDZrrib: case X86::VCMPPDZrribk:
153 case X86::VCMPPSZrrib: case X86::VCMPPSZrribk:
154 case X86::VCMPSDZrrb_Int: case X86::VCMPSDZrrb_Intk:
155 case X86::VCMPSSZrrb_Int: case X86::VCMPSSZrrb_Intk:
156 if (Imm >= 0 && Imm <= 31) {
157 OS << '\t';
158 printCMPMnemonic(MI, /*IsVCMP*/true, OS);
159
160 unsigned CurOp = (Desc.TSFlags & X86II::EVEX_K) ? 3 : 2;
161
162 if ((Desc.TSFlags & X86II::FormMask) == X86II::MRMSrcMem) {
163 if (Desc.TSFlags & X86II::EVEX_B) {
164 // Broadcast form.
165 // Load size is based on W-bit.
166 if (Desc.TSFlags & X86II::VEX_W)
167 printqwordmem(MI, CurOp--, OS);
168 else
169 printdwordmem(MI, CurOp--, OS);
170
171 // Print the number of elements broadcasted.
172 unsigned NumElts;
173 if (Desc.TSFlags & X86II::EVEX_L2)
174 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 8 : 16;
175 else if (Desc.TSFlags & X86II::VEX_L)
176 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 4 : 8;
177 else
178 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 2 : 4;
179 OS << "{1to" << NumElts << "}";
180 } else {
181 if ((Desc.TSFlags & X86II::OpPrefixMask) == X86II::XS)
182 printdwordmem(MI, CurOp--, OS);
183 else if ((Desc.TSFlags & X86II::OpPrefixMask) == X86II::XD)
184 printqwordmem(MI, CurOp--, OS);
185 else if (Desc.TSFlags & X86II::EVEX_L2)
186 printzmmwordmem(MI, CurOp--, OS);
187 else if (Desc.TSFlags & X86II::VEX_L)
188 printymmwordmem(MI, CurOp--, OS);
189 else
190 printxmmwordmem(MI, CurOp--, OS);
191 }
192 } else {
193 if (Desc.TSFlags & X86II::EVEX_B)
194 OS << "{sae}, ";
195 printOperand(MI, CurOp--, OS);
196 }
197
198 OS << ", ";
199 printOperand(MI, CurOp--, OS);
200 OS << ", ";
201 printOperand(MI, 0, OS);
202 if (CurOp > 0) {
203 // Print mask operand.
204 OS << " {";
205 printOperand(MI, CurOp--, OS);
206 OS << "}";
207 }
208
209 return true;
210 }
211 break;
212
213 case X86::VPCOMBmi: case X86::VPCOMBri:
214 case X86::VPCOMDmi: case X86::VPCOMDri:
215 case X86::VPCOMQmi: case X86::VPCOMQri:
216 case X86::VPCOMUBmi: case X86::VPCOMUBri:
217 case X86::VPCOMUDmi: case X86::VPCOMUDri:
218 case X86::VPCOMUQmi: case X86::VPCOMUQri:
219 case X86::VPCOMUWmi: case X86::VPCOMUWri:
220 case X86::VPCOMWmi: case X86::VPCOMWri:
221 if (Imm >= 0 && Imm <= 7) {
222 OS << '\t';
223 printVPCOMMnemonic(MI, OS);
224
225 if ((Desc.TSFlags & X86II::FormMask) == X86II::MRMSrcMem)
226 printxmmwordmem(MI, 2, OS);
227 else
228 printOperand(MI, 2, OS);
229
230 OS << ", ";
231 printOperand(MI, 1, OS);
232 OS << ", ";
233 printOperand(MI, 0, OS);
234 return true;
235 }
236 break;
237
238 case X86::VPCMPBZ128rmi: case X86::VPCMPBZ128rri:
239 case X86::VPCMPBZ256rmi: case X86::VPCMPBZ256rri:
240 case X86::VPCMPBZrmi: case X86::VPCMPBZrri:
241 case X86::VPCMPDZ128rmi: case X86::VPCMPDZ128rri:
242 case X86::VPCMPDZ256rmi: case X86::VPCMPDZ256rri:
243 case X86::VPCMPDZrmi: case X86::VPCMPDZrri:
244 case X86::VPCMPQZ128rmi: case X86::VPCMPQZ128rri:
245 case X86::VPCMPQZ256rmi: case X86::VPCMPQZ256rri:
246 case X86::VPCMPQZrmi: case X86::VPCMPQZrri:
247 case X86::VPCMPUBZ128rmi: case X86::VPCMPUBZ128rri:
248 case X86::VPCMPUBZ256rmi: case X86::VPCMPUBZ256rri:
249 case X86::VPCMPUBZrmi: case X86::VPCMPUBZrri:
250 case X86::VPCMPUDZ128rmi: case X86::VPCMPUDZ128rri:
251 case X86::VPCMPUDZ256rmi: case X86::VPCMPUDZ256rri:
252 case X86::VPCMPUDZrmi: case X86::VPCMPUDZrri:
253 case X86::VPCMPUQZ128rmi: case X86::VPCMPUQZ128rri:
254 case X86::VPCMPUQZ256rmi: case X86::VPCMPUQZ256rri:
255 case X86::VPCMPUQZrmi: case X86::VPCMPUQZrri:
256 case X86::VPCMPUWZ128rmi: case X86::VPCMPUWZ128rri:
257 case X86::VPCMPUWZ256rmi: case X86::VPCMPUWZ256rri:
258 case X86::VPCMPUWZrmi: case X86::VPCMPUWZrri:
259 case X86::VPCMPWZ128rmi: case X86::VPCMPWZ128rri:
260 case X86::VPCMPWZ256rmi: case X86::VPCMPWZ256rri:
261 case X86::VPCMPWZrmi: case X86::VPCMPWZrri:
262 case X86::VPCMPBZ128rmik: case X86::VPCMPBZ128rrik:
263 case X86::VPCMPBZ256rmik: case X86::VPCMPBZ256rrik:
264 case X86::VPCMPBZrmik: case X86::VPCMPBZrrik:
265 case X86::VPCMPDZ128rmik: case X86::VPCMPDZ128rrik:
266 case X86::VPCMPDZ256rmik: case X86::VPCMPDZ256rrik:
267 case X86::VPCMPDZrmik: case X86::VPCMPDZrrik:
268 case X86::VPCMPQZ128rmik: case X86::VPCMPQZ128rrik:
269 case X86::VPCMPQZ256rmik: case X86::VPCMPQZ256rrik:
270 case X86::VPCMPQZrmik: case X86::VPCMPQZrrik:
271 case X86::VPCMPUBZ128rmik: case X86::VPCMPUBZ128rrik:
272 case X86::VPCMPUBZ256rmik: case X86::VPCMPUBZ256rrik:
273 case X86::VPCMPUBZrmik: case X86::VPCMPUBZrrik:
274 case X86::VPCMPUDZ128rmik: case X86::VPCMPUDZ128rrik:
275 case X86::VPCMPUDZ256rmik: case X86::VPCMPUDZ256rrik:
276 case X86::VPCMPUDZrmik: case X86::VPCMPUDZrrik:
277 case X86::VPCMPUQZ128rmik: case X86::VPCMPUQZ128rrik:
278 case X86::VPCMPUQZ256rmik: case X86::VPCMPUQZ256rrik:
279 case X86::VPCMPUQZrmik: case X86::VPCMPUQZrrik:
280 case X86::VPCMPUWZ128rmik: case X86::VPCMPUWZ128rrik:
281 case X86::VPCMPUWZ256rmik: case X86::VPCMPUWZ256rrik:
282 case X86::VPCMPUWZrmik: case X86::VPCMPUWZrrik:
283 case X86::VPCMPWZ128rmik: case X86::VPCMPWZ128rrik:
284 case X86::VPCMPWZ256rmik: case X86::VPCMPWZ256rrik:
285 case X86::VPCMPWZrmik: case X86::VPCMPWZrrik:
286 case X86::VPCMPDZ128rmib: case X86::VPCMPDZ128rmibk:
287 case X86::VPCMPDZ256rmib: case X86::VPCMPDZ256rmibk:
288 case X86::VPCMPDZrmib: case X86::VPCMPDZrmibk:
289 case X86::VPCMPQZ128rmib: case X86::VPCMPQZ128rmibk:
290 case X86::VPCMPQZ256rmib: case X86::VPCMPQZ256rmibk:
291 case X86::VPCMPQZrmib: case X86::VPCMPQZrmibk:
292 case X86::VPCMPUDZ128rmib: case X86::VPCMPUDZ128rmibk:
293 case X86::VPCMPUDZ256rmib: case X86::VPCMPUDZ256rmibk:
294 case X86::VPCMPUDZrmib: case X86::VPCMPUDZrmibk:
295 case X86::VPCMPUQZ128rmib: case X86::VPCMPUQZ128rmibk:
296 case X86::VPCMPUQZ256rmib: case X86::VPCMPUQZ256rmibk:
297 case X86::VPCMPUQZrmib: case X86::VPCMPUQZrmibk:
298 if ((Imm >= 0 && Imm <= 2) || (Imm >= 4 && Imm <= 6)) {
299 OS << '\t';
300 printVPCMPMnemonic(MI, OS);
301
302 unsigned CurOp = (Desc.TSFlags & X86II::EVEX_K) ? 3 : 2;
303
304 if ((Desc.TSFlags & X86II::FormMask) == X86II::MRMSrcMem) {
305 if (Desc.TSFlags & X86II::EVEX_B) {
306 // Broadcast form.
307 // Load size is based on W-bit as only D and Q are supported.
308 if (Desc.TSFlags & X86II::VEX_W)
309 printqwordmem(MI, CurOp--, OS);
310 else
311 printdwordmem(MI, CurOp--, OS);
312
313 // Print the number of elements broadcasted.
314 unsigned NumElts;
315 if (Desc.TSFlags & X86II::EVEX_L2)
316 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 8 : 16;
317 else if (Desc.TSFlags & X86II::VEX_L)
318 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 4 : 8;
319 else
320 NumElts = (Desc.TSFlags & X86II::VEX_W) ? 2 : 4;
321 OS << "{1to" << NumElts << "}";
322 } else {
323 if (Desc.TSFlags & X86II::EVEX_L2)
324 printzmmwordmem(MI, CurOp--, OS);
325 else if (Desc.TSFlags & X86II::VEX_L)
326 printymmwordmem(MI, CurOp--, OS);
327 else
328 printxmmwordmem(MI, CurOp--, OS);
329 }
330 } else {
331 printOperand(MI, CurOp--, OS);
332 }
333
334 OS << ", ";
335 printOperand(MI, CurOp--, OS);
336 OS << ", ";
337 printOperand(MI, 0, OS);
338 if (CurOp > 0) {
339 // Print mask operand.
340 OS << " {";
341 printOperand(MI, CurOp--, OS);
342 OS << "}";
343 }
344
345 return true;
346 }
347 break;
348 }
349
350 return false;
351 }
352
printOperand(const MCInst * MI,unsigned OpNo,raw_ostream & O)353 void X86ATTInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
354 raw_ostream &O) {
355 const MCOperand &Op = MI->getOperand(OpNo);
356 if (Op.isReg()) {
357 printRegName(O, Op.getReg());
358 } else if (Op.isImm()) {
359 // Print immediates as signed values.
360 int64_t Imm = Op.getImm();
361 O << markup("<imm:") << '$' << formatImm(Imm) << markup(">");
362
363 // TODO: This should be in a helper function in the base class, so it can
364 // be used by other printers.
365
366 // If there are no instruction-specific comments, add a comment clarifying
367 // the hex value of the immediate operand when it isn't in the range
368 // [-256,255].
369 if (CommentStream && !HasCustomInstComment && (Imm > 255 || Imm < -256)) {
370 // Don't print unnecessary hex sign bits.
371 if (Imm == (int16_t)(Imm))
372 *CommentStream << format("imm = 0x%" PRIX16 "\n", (uint16_t)Imm);
373 else if (Imm == (int32_t)(Imm))
374 *CommentStream << format("imm = 0x%" PRIX32 "\n", (uint32_t)Imm);
375 else
376 *CommentStream << format("imm = 0x%" PRIX64 "\n", (uint64_t)Imm);
377 }
378 } else {
379 assert(Op.isExpr() && "unknown operand kind in printOperand");
380 O << markup("<imm:") << '$';
381 Op.getExpr()->print(O, &MAI);
382 O << markup(">");
383 }
384 }
385
printMemReference(const MCInst * MI,unsigned Op,raw_ostream & O)386 void X86ATTInstPrinter::printMemReference(const MCInst *MI, unsigned Op,
387 raw_ostream &O) {
388 const MCOperand &BaseReg = MI->getOperand(Op + X86::AddrBaseReg);
389 const MCOperand &IndexReg = MI->getOperand(Op + X86::AddrIndexReg);
390 const MCOperand &DispSpec = MI->getOperand(Op + X86::AddrDisp);
391
392 O << markup("<mem:");
393
394 // If this has a segment register, print it.
395 printOptionalSegReg(MI, Op + X86::AddrSegmentReg, O);
396
397 if (DispSpec.isImm()) {
398 int64_t DispVal = DispSpec.getImm();
399 if (DispVal || (!IndexReg.getReg() && !BaseReg.getReg()))
400 O << formatImm(DispVal);
401 } else {
402 assert(DispSpec.isExpr() && "non-immediate displacement for LEA?");
403 DispSpec.getExpr()->print(O, &MAI);
404 }
405
406 if (IndexReg.getReg() || BaseReg.getReg()) {
407 O << '(';
408 if (BaseReg.getReg())
409 printOperand(MI, Op + X86::AddrBaseReg, O);
410
411 if (IndexReg.getReg()) {
412 O << ',';
413 printOperand(MI, Op + X86::AddrIndexReg, O);
414 unsigned ScaleVal = MI->getOperand(Op + X86::AddrScaleAmt).getImm();
415 if (ScaleVal != 1) {
416 O << ',' << markup("<imm:") << ScaleVal // never printed in hex.
417 << markup(">");
418 }
419 }
420 O << ')';
421 }
422
423 O << markup(">");
424 }
425
printSrcIdx(const MCInst * MI,unsigned Op,raw_ostream & O)426 void X86ATTInstPrinter::printSrcIdx(const MCInst *MI, unsigned Op,
427 raw_ostream &O) {
428 O << markup("<mem:");
429
430 // If this has a segment register, print it.
431 printOptionalSegReg(MI, Op + 1, O);
432
433 O << "(";
434 printOperand(MI, Op, O);
435 O << ")";
436
437 O << markup(">");
438 }
439
printDstIdx(const MCInst * MI,unsigned Op,raw_ostream & O)440 void X86ATTInstPrinter::printDstIdx(const MCInst *MI, unsigned Op,
441 raw_ostream &O) {
442 O << markup("<mem:");
443
444 O << "%es:(";
445 printOperand(MI, Op, O);
446 O << ")";
447
448 O << markup(">");
449 }
450
printMemOffset(const MCInst * MI,unsigned Op,raw_ostream & O)451 void X86ATTInstPrinter::printMemOffset(const MCInst *MI, unsigned Op,
452 raw_ostream &O) {
453 const MCOperand &DispSpec = MI->getOperand(Op);
454
455 O << markup("<mem:");
456
457 // If this has a segment register, print it.
458 printOptionalSegReg(MI, Op + 1, O);
459
460 if (DispSpec.isImm()) {
461 O << formatImm(DispSpec.getImm());
462 } else {
463 assert(DispSpec.isExpr() && "non-immediate displacement?");
464 DispSpec.getExpr()->print(O, &MAI);
465 }
466
467 O << markup(">");
468 }
469
printU8Imm(const MCInst * MI,unsigned Op,raw_ostream & O)470 void X86ATTInstPrinter::printU8Imm(const MCInst *MI, unsigned Op,
471 raw_ostream &O) {
472 if (MI->getOperand(Op).isExpr())
473 return printOperand(MI, Op, O);
474
475 O << markup("<imm:") << '$' << formatImm(MI->getOperand(Op).getImm() & 0xff)
476 << markup(">");
477 }
478
printSTiRegOperand(const MCInst * MI,unsigned OpNo,raw_ostream & OS)479 void X86ATTInstPrinter::printSTiRegOperand(const MCInst *MI, unsigned OpNo,
480 raw_ostream &OS) {
481 const MCOperand &Op = MI->getOperand(OpNo);
482 unsigned Reg = Op.getReg();
483 // Override the default printing to print st(0) instead st.
484 if (Reg == X86::ST0)
485 OS << markup("<reg:") << "%st(0)" << markup(">");
486 else
487 printRegName(OS, Reg);
488 }
489