1 //===-- SIFixSGPRCopies.cpp - Remove potential VGPR => SGPR copies --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// Copies from VGPR to SGPR registers are illegal and the register coalescer
12 /// will sometimes generate these illegal copies in situations like this:
14 /// Register Class <vsrc> is the union of <vgpr> and <sgpr>
17 /// %vreg0 <sgpr> = SCALAR_INST
18 /// %vreg1 <vsrc> = COPY %vreg0 <sgpr>
20 /// BRANCH %cond BB1, BB2
22 /// %vreg2 <vgpr> = VECTOR_INST
23 /// %vreg3 <vsrc> = COPY %vreg2 <vgpr>
25 /// %vreg4 <vsrc> = PHI %vreg1 <vsrc>, <BB#0>, %vreg3 <vrsc>, <BB#1>
26 /// %vreg5 <vgpr> = VECTOR_INST %vreg4 <vsrc>
29 /// The coalescer will begin at BB0 and eliminate its copy, then the resulting
30 /// code will look like this:
33 /// %vreg0 <sgpr> = SCALAR_INST
35 /// BRANCH %cond BB1, BB2
37 /// %vreg2 <vgpr> = VECTOR_INST
38 /// %vreg3 <vsrc> = COPY %vreg2 <vgpr>
40 /// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <vsrc>, <BB#1>
41 /// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr>
43 /// Now that the result of the PHI instruction is an SGPR, the register
44 /// allocator is now forced to constrain the register class of %vreg3 to
45 /// <sgpr> so we end up with final code like this:
48 /// %vreg0 <sgpr> = SCALAR_INST
50 /// BRANCH %cond BB1, BB2
52 /// %vreg2 <vgpr> = VECTOR_INST
53 /// %vreg3 <sgpr> = COPY %vreg2 <vgpr>
55 /// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <sgpr>, <BB#1>
56 /// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr>
58 /// Now this code contains an illegal copy from a VGPR to an SGPR.
60 /// In order to avoid this problem, this pass searches for PHI instructions
61 /// which define a <vsrc> register and constrains its definition class to
62 /// <vgpr> if the user of the PHI's definition register is a vector instruction.
63 /// If the PHI's definition class is constrained to <vgpr> then the coalescer
64 /// will be unable to perform the COPY removal from the above example which
65 /// ultimately led to the creation of an illegal COPY.
66 //===----------------------------------------------------------------------===//
69 #include "AMDGPUSubtarget.h"
70 #include "SIInstrInfo.h"
71 #include "llvm/CodeGen/MachineFunctionPass.h"
72 #include "llvm/CodeGen/MachineInstrBuilder.h"
73 #include "llvm/CodeGen/MachineRegisterInfo.h"
74 #include "llvm/Support/Debug.h"
75 #include "llvm/Support/raw_ostream.h"
76 #include "llvm/Target/TargetMachine.h"
80 #define DEBUG_TYPE "sgpr-copies"
84 class SIFixSGPRCopies : public MachineFunctionPass {
90 SIFixSGPRCopies(TargetMachine &tm) : MachineFunctionPass(ID) { }
92 bool runOnMachineFunction(MachineFunction &MF) override;
94 const char *getPassName() const override {
95 return "SI Fix SGPR copies";
98 void getAnalysisUsage(AnalysisUsage &AU) const override {
100 MachineFunctionPass::getAnalysisUsage(AU);
104 } // End anonymous namespace
106 char SIFixSGPRCopies::ID = 0;
108 FunctionPass *llvm::createSIFixSGPRCopiesPass(TargetMachine &tm) {
109 return new SIFixSGPRCopies(tm);
112 static bool hasVGPROperands(const MachineInstr &MI, const SIRegisterInfo *TRI) {
113 const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
114 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
115 if (!MI.getOperand(i).isReg() ||
116 !TargetRegisterInfo::isVirtualRegister(MI.getOperand(i).getReg()))
119 if (TRI->hasVGPRs(MRI.getRegClass(MI.getOperand(i).getReg())))
125 static std::pair<const TargetRegisterClass *, const TargetRegisterClass *>
126 getCopyRegClasses(const MachineInstr &Copy,
127 const SIRegisterInfo &TRI,
128 const MachineRegisterInfo &MRI) {
129 unsigned DstReg = Copy.getOperand(0).getReg();
130 unsigned SrcReg = Copy.getOperand(1).getReg();
132 const TargetRegisterClass *SrcRC =
133 TargetRegisterInfo::isVirtualRegister(SrcReg) ?
134 MRI.getRegClass(SrcReg) :
135 TRI.getPhysRegClass(SrcReg);
137 // We don't really care about the subregister here.
138 // SrcRC = TRI.getSubRegClass(SrcRC, Copy.getOperand(1).getSubReg());
140 const TargetRegisterClass *DstRC =
141 TargetRegisterInfo::isVirtualRegister(DstReg) ?
142 MRI.getRegClass(DstReg) :
143 TRI.getPhysRegClass(DstReg);
145 return std::make_pair(SrcRC, DstRC);
148 static bool isVGPRToSGPRCopy(const TargetRegisterClass *SrcRC,
149 const TargetRegisterClass *DstRC,
150 const SIRegisterInfo &TRI) {
151 return TRI.isSGPRClass(DstRC) && TRI.hasVGPRs(SrcRC);
154 static bool isSGPRToVGPRCopy(const TargetRegisterClass *SrcRC,
155 const TargetRegisterClass *DstRC,
156 const SIRegisterInfo &TRI) {
157 return TRI.isSGPRClass(SrcRC) && TRI.hasVGPRs(DstRC);
160 // Distribute an SGPR->VGPR copy of a REG_SEQUENCE into a VGPR REG_SEQUENCE.
163 // SGPRy = REG_SEQUENCE SGPRx, sub0 ...
164 // VGPRz = COPY SGPRy
168 // VGPRx = COPY SGPRx
169 // VGPRz = REG_SEQUENCE VGPRx, sub0
171 // This exposes immediate folding opportunities when materializing 64-bit
173 static bool foldVGPRCopyIntoRegSequence(MachineInstr &MI,
174 const SIRegisterInfo *TRI,
175 const SIInstrInfo *TII,
176 MachineRegisterInfo &MRI) {
177 assert(MI.isRegSequence());
179 unsigned DstReg = MI.getOperand(0).getReg();
180 if (!TRI->isSGPRClass(MRI.getRegClass(DstReg)))
183 if (!MRI.hasOneUse(DstReg))
186 MachineInstr &CopyUse = *MRI.use_instr_begin(DstReg);
187 if (!CopyUse.isCopy())
190 const TargetRegisterClass *SrcRC, *DstRC;
191 std::tie(SrcRC, DstRC) = getCopyRegClasses(CopyUse, *TRI, MRI);
193 if (!isSGPRToVGPRCopy(SrcRC, DstRC, *TRI))
196 // TODO: Could have multiple extracts?
197 unsigned SubReg = CopyUse.getOperand(1).getSubReg();
198 if (SubReg != AMDGPU::NoSubRegister)
201 MRI.setRegClass(DstReg, DstRC);
204 // SGPRy = REG_SEQUENCE SGPRx, sub0 ...
205 // VGPRz = COPY SGPRy
208 // VGPRx = COPY SGPRx
209 // VGPRz = REG_SEQUENCE VGPRx, sub0
211 MI.getOperand(0).setReg(CopyUse.getOperand(0).getReg());
213 for (unsigned I = 1, N = MI.getNumOperands(); I != N; I += 2) {
214 unsigned SrcReg = MI.getOperand(I).getReg();
215 unsigned SrcSubReg = MI.getOperand(I).getReg();
217 const TargetRegisterClass *SrcRC = MRI.getRegClass(SrcReg);
218 assert(TRI->isSGPRClass(SrcRC) &&
219 "Expected SGPR REG_SEQUENCE to only have SGPR inputs");
221 SrcRC = TRI->getSubRegClass(SrcRC, SrcSubReg);
222 const TargetRegisterClass *NewSrcRC = TRI->getEquivalentVGPRClass(SrcRC);
224 unsigned TmpReg = MRI.createVirtualRegister(NewSrcRC);
226 BuildMI(*MI.getParent(), &MI, MI.getDebugLoc(), TII->get(AMDGPU::COPY), TmpReg)
227 .addOperand(MI.getOperand(I));
229 MI.getOperand(I).setReg(TmpReg);
232 CopyUse.eraseFromParent();
236 bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) {
237 MachineRegisterInfo &MRI = MF.getRegInfo();
238 const SIRegisterInfo *TRI =
239 static_cast<const SIRegisterInfo *>(MF.getSubtarget().getRegisterInfo());
240 const SIInstrInfo *TII =
241 static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
242 for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
245 MachineBasicBlock &MBB = *BI;
246 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
248 MachineInstr &MI = *I;
250 switch (MI.getOpcode()) {
254 // If the destination register is a physical register there isn't really
255 // much we can do to fix this.
256 if (!TargetRegisterInfo::isVirtualRegister(MI.getOperand(0).getReg()))
259 const TargetRegisterClass *SrcRC, *DstRC;
260 std::tie(SrcRC, DstRC) = getCopyRegClasses(MI, *TRI, MRI);
261 if (isVGPRToSGPRCopy(SrcRC, DstRC, *TRI)) {
262 DEBUG(dbgs() << "Fixing VGPR -> SGPR copy: " << MI);
269 DEBUG(dbgs() << "Fixing PHI: " << MI);
270 unsigned Reg = MI.getOperand(0).getReg();
271 if (!TRI->isSGPRClass(MRI.getRegClass(Reg)))
274 // If a PHI node defines an SGPR and any of its operands are VGPRs,
275 // then we need to move it to the VALU.
277 // Also, if a PHI node defines an SGPR and has all SGPR operands
278 // we must move it to the VALU, because the SGPR operands will
279 // all end up being assigned the same register, which means
280 // there is a potential for a conflict if different threads take
281 // different control flow paths.
289 // sgpr2 = PHI sgpr0, sgpr1
300 // FIXME: This is OK if the branching decision is made based on an
302 bool SGPRBranch = false;
304 // The one exception to this rule is when one of the operands
305 // is defined by a SI_BREAK, SI_IF_BREAK, or SI_ELSE_BREAK
306 // instruction. In this case, there we know the program will
307 // never enter the second block (the loop) without entering
308 // the first block (where the condition is computed), so there
309 // is no chance for values to be over-written.
311 bool HasBreakDef = false;
312 for (unsigned i = 1; i < MI.getNumOperands(); i+=2) {
313 unsigned Reg = MI.getOperand(i).getReg();
314 if (TRI->hasVGPRs(MRI.getRegClass(Reg))) {
318 MachineInstr *DefInstr = MRI.getUniqueVRegDef(Reg);
320 switch(DefInstr->getOpcode()) {
322 case AMDGPU::SI_BREAK:
323 case AMDGPU::SI_IF_BREAK:
324 case AMDGPU::SI_ELSE_BREAK:
325 // If we see a PHI instruction that defines an SGPR, then that PHI
326 // instruction has already been considered and should have
327 // a *_BREAK as an operand.
334 if (!SGPRBranch && !HasBreakDef)
338 case AMDGPU::REG_SEQUENCE: {
339 if (TRI->hasVGPRs(TII->getOpRegClass(MI, 0)) ||
340 !hasVGPROperands(MI, TRI)) {
341 foldVGPRCopyIntoRegSequence(MI, TRI, TII, MRI);
345 DEBUG(dbgs() << "Fixing REG_SEQUENCE: " << MI);
350 case AMDGPU::INSERT_SUBREG: {
351 const TargetRegisterClass *DstRC, *Src0RC, *Src1RC;
352 DstRC = MRI.getRegClass(MI.getOperand(0).getReg());
353 Src0RC = MRI.getRegClass(MI.getOperand(1).getReg());
354 Src1RC = MRI.getRegClass(MI.getOperand(2).getReg());
355 if (TRI->isSGPRClass(DstRC) &&
356 (TRI->hasVGPRs(Src0RC) || TRI->hasVGPRs(Src1RC))) {
357 DEBUG(dbgs() << " Fixing INSERT_SUBREG: " << MI);