1 //===-- CallingConvLower.cpp - Calling Conventions ------------------------===//
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 implements the CCState class, used for lowering and implementing
10 // calling conventions.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/CodeGen/CallingConvLower.h"
15 #include "llvm/CodeGen/MachineFrameInfo.h"
16 #include "llvm/CodeGen/MachineRegisterInfo.h"
17 #include "llvm/CodeGen/TargetLowering.h"
18 #include "llvm/CodeGen/TargetRegisterInfo.h"
19 #include "llvm/CodeGen/TargetSubtargetInfo.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/ErrorHandling.h"
23 #include "llvm/Support/SaveAndRestore.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include <algorithm>
26 
27 using namespace llvm;
28 
29 CCState::CCState(CallingConv::ID CC, bool isVarArg, MachineFunction &mf,
30                  SmallVectorImpl<CCValAssign> &locs, LLVMContext &C)
31     : CallingConv(CC), IsVarArg(isVarArg), MF(mf),
32       TRI(*MF.getSubtarget().getRegisterInfo()), Locs(locs), Context(C) {
33   // No stack is used.
34   StackOffset = 0;
35 
36   clearByValRegsInfo();
37   UsedRegs.resize((TRI.getNumRegs()+31)/32);
38 }
39 
40 /// Allocate space on the stack large enough to pass an argument by value.
41 /// The size and alignment information of the argument is encoded in
42 /// its parameter attribute.
43 void CCState::HandleByVal(unsigned ValNo, MVT ValVT, MVT LocVT,
44                           CCValAssign::LocInfo LocInfo, int MinSize,
45                           int MinAlignment, ISD::ArgFlagsTy ArgFlags) {
46   Align MinAlign(MinAlignment);
47   Align Alignment(ArgFlags.getByValAlign());
48   unsigned Size  = ArgFlags.getByValSize();
49   if (MinSize > (int)Size)
50     Size = MinSize;
51   if (MinAlign > Alignment)
52     Alignment = MinAlign;
53   ensureMaxAlignment(Alignment);
54   MF.getSubtarget().getTargetLowering()->HandleByVal(this, Size,
55                                                      Alignment.value());
56   Size = unsigned(alignTo(Size, MinAlign));
57   unsigned Offset = AllocateStack(Size, Alignment.value());
58   addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
59 }
60 
61 /// Mark a register and all of its aliases as allocated.
62 void CCState::MarkAllocated(unsigned Reg) {
63   for (MCRegAliasIterator AI(Reg, &TRI, true); AI.isValid(); ++AI)
64     UsedRegs[*AI/32] |= 1 << (*AI&31);
65 }
66 
67 bool CCState::IsShadowAllocatedReg(unsigned Reg) const {
68   if (!isAllocated(Reg))
69     return false;
70 
71   for (auto const &ValAssign : Locs) {
72     if (ValAssign.isRegLoc()) {
73       for (MCRegAliasIterator AI(ValAssign.getLocReg(), &TRI, true);
74            AI.isValid(); ++AI) {
75         if (*AI == Reg)
76           return false;
77       }
78     }
79   }
80   return true;
81 }
82 
83 /// Analyze an array of argument values,
84 /// incorporating info about the formals into this state.
85 void
86 CCState::AnalyzeFormalArguments(const SmallVectorImpl<ISD::InputArg> &Ins,
87                                 CCAssignFn Fn) {
88   unsigned NumArgs = Ins.size();
89 
90   for (unsigned i = 0; i != NumArgs; ++i) {
91     MVT ArgVT = Ins[i].VT;
92     ISD::ArgFlagsTy ArgFlags = Ins[i].Flags;
93     if (Fn(i, ArgVT, ArgVT, CCValAssign::Full, ArgFlags, *this))
94       report_fatal_error("unable to allocate function argument #" + Twine(i));
95   }
96 }
97 
98 /// Analyze the return values of a function, returning true if the return can
99 /// be performed without sret-demotion and false otherwise.
100 bool CCState::CheckReturn(const SmallVectorImpl<ISD::OutputArg> &Outs,
101                           CCAssignFn Fn) {
102   // Determine which register each value should be copied into.
103   for (unsigned i = 0, e = Outs.size(); i != e; ++i) {
104     MVT VT = Outs[i].VT;
105     ISD::ArgFlagsTy ArgFlags = Outs[i].Flags;
106     if (Fn(i, VT, VT, CCValAssign::Full, ArgFlags, *this))
107       return false;
108   }
109   return true;
110 }
111 
112 /// Analyze the returned values of a return,
113 /// incorporating info about the result values into this state.
114 void CCState::AnalyzeReturn(const SmallVectorImpl<ISD::OutputArg> &Outs,
115                             CCAssignFn Fn) {
116   // Determine which register each value should be copied into.
117   for (unsigned i = 0, e = Outs.size(); i != e; ++i) {
118     MVT VT = Outs[i].VT;
119     ISD::ArgFlagsTy ArgFlags = Outs[i].Flags;
120     if (Fn(i, VT, VT, CCValAssign::Full, ArgFlags, *this))
121       report_fatal_error("unable to allocate function return #" + Twine(i));
122   }
123 }
124 
125 /// Analyze the outgoing arguments to a call,
126 /// incorporating info about the passed values into this state.
127 void CCState::AnalyzeCallOperands(const SmallVectorImpl<ISD::OutputArg> &Outs,
128                                   CCAssignFn Fn) {
129   unsigned NumOps = Outs.size();
130   for (unsigned i = 0; i != NumOps; ++i) {
131     MVT ArgVT = Outs[i].VT;
132     ISD::ArgFlagsTy ArgFlags = Outs[i].Flags;
133     if (Fn(i, ArgVT, ArgVT, CCValAssign::Full, ArgFlags, *this)) {
134 #ifndef NDEBUG
135       dbgs() << "Call operand #" << i << " has unhandled type "
136              << EVT(ArgVT).getEVTString() << '\n';
137 #endif
138       llvm_unreachable(nullptr);
139     }
140   }
141 }
142 
143 /// Same as above except it takes vectors of types and argument flags.
144 void CCState::AnalyzeCallOperands(SmallVectorImpl<MVT> &ArgVTs,
145                                   SmallVectorImpl<ISD::ArgFlagsTy> &Flags,
146                                   CCAssignFn Fn) {
147   unsigned NumOps = ArgVTs.size();
148   for (unsigned i = 0; i != NumOps; ++i) {
149     MVT ArgVT = ArgVTs[i];
150     ISD::ArgFlagsTy ArgFlags = Flags[i];
151     if (Fn(i, ArgVT, ArgVT, CCValAssign::Full, ArgFlags, *this)) {
152 #ifndef NDEBUG
153       dbgs() << "Call operand #" << i << " has unhandled type "
154              << EVT(ArgVT).getEVTString() << '\n';
155 #endif
156       llvm_unreachable(nullptr);
157     }
158   }
159 }
160 
161 /// Analyze the return values of a call, incorporating info about the passed
162 /// values into this state.
163 void CCState::AnalyzeCallResult(const SmallVectorImpl<ISD::InputArg> &Ins,
164                                 CCAssignFn Fn) {
165   for (unsigned i = 0, e = Ins.size(); i != e; ++i) {
166     MVT VT = Ins[i].VT;
167     ISD::ArgFlagsTy Flags = Ins[i].Flags;
168     if (Fn(i, VT, VT, CCValAssign::Full, Flags, *this)) {
169 #ifndef NDEBUG
170       dbgs() << "Call result #" << i << " has unhandled type "
171              << EVT(VT).getEVTString() << '\n';
172 #endif
173       llvm_unreachable(nullptr);
174     }
175   }
176 }
177 
178 /// Same as above except it's specialized for calls that produce a single value.
179 void CCState::AnalyzeCallResult(MVT VT, CCAssignFn Fn) {
180   if (Fn(0, VT, VT, CCValAssign::Full, ISD::ArgFlagsTy(), *this)) {
181 #ifndef NDEBUG
182     dbgs() << "Call result has unhandled type "
183            << EVT(VT).getEVTString() << '\n';
184 #endif
185     llvm_unreachable(nullptr);
186   }
187 }
188 
189 static bool isValueTypeInRegForCC(CallingConv::ID CC, MVT VT) {
190   if (VT.isVector())
191     return true; // Assume -msse-regparm might be in effect.
192   if (!VT.isInteger())
193     return false;
194   if (CC == CallingConv::X86_VectorCall || CC == CallingConv::X86_FastCall)
195     return true;
196   return false;
197 }
198 
199 void CCState::getRemainingRegParmsForType(SmallVectorImpl<MCPhysReg> &Regs,
200                                           MVT VT, CCAssignFn Fn) {
201   unsigned SavedStackOffset = StackOffset;
202   Align SavedMaxStackArgAlign = MaxStackArgAlign;
203   unsigned NumLocs = Locs.size();
204 
205   // Set the 'inreg' flag if it is used for this calling convention.
206   ISD::ArgFlagsTy Flags;
207   if (isValueTypeInRegForCC(CallingConv, VT))
208     Flags.setInReg();
209 
210   // Allocate something of this value type repeatedly until we get assigned a
211   // location in memory.
212   bool HaveRegParm = true;
213   while (HaveRegParm) {
214     if (Fn(0, VT, VT, CCValAssign::Full, Flags, *this)) {
215 #ifndef NDEBUG
216       dbgs() << "Call has unhandled type " << EVT(VT).getEVTString()
217              << " while computing remaining regparms\n";
218 #endif
219       llvm_unreachable(nullptr);
220     }
221     HaveRegParm = Locs.back().isRegLoc();
222   }
223 
224   // Copy all the registers from the value locations we added.
225   assert(NumLocs < Locs.size() && "CC assignment failed to add location");
226   for (unsigned I = NumLocs, E = Locs.size(); I != E; ++I)
227     if (Locs[I].isRegLoc())
228       Regs.push_back(MCPhysReg(Locs[I].getLocReg()));
229 
230   // Clear the assigned values and stack memory. We leave the registers marked
231   // as allocated so that future queries don't return the same registers, i.e.
232   // when i64 and f64 are both passed in GPRs.
233   StackOffset = SavedStackOffset;
234   MaxStackArgAlign = SavedMaxStackArgAlign;
235   Locs.resize(NumLocs);
236 }
237 
238 void CCState::analyzeMustTailForwardedRegisters(
239     SmallVectorImpl<ForwardedRegister> &Forwards, ArrayRef<MVT> RegParmTypes,
240     CCAssignFn Fn) {
241   // Oftentimes calling conventions will not user register parameters for
242   // variadic functions, so we need to assume we're not variadic so that we get
243   // all the registers that might be used in a non-variadic call.
244   SaveAndRestore<bool> SavedVarArg(IsVarArg, false);
245   SaveAndRestore<bool> SavedMustTail(AnalyzingMustTailForwardedRegs, true);
246 
247   for (MVT RegVT : RegParmTypes) {
248     SmallVector<MCPhysReg, 8> RemainingRegs;
249     getRemainingRegParmsForType(RemainingRegs, RegVT, Fn);
250     const TargetLowering *TL = MF.getSubtarget().getTargetLowering();
251     const TargetRegisterClass *RC = TL->getRegClassFor(RegVT);
252     for (MCPhysReg PReg : RemainingRegs) {
253       unsigned VReg = MF.addLiveIn(PReg, RC);
254       Forwards.push_back(ForwardedRegister(VReg, PReg, RegVT));
255     }
256   }
257 }
258 
259 bool CCState::resultsCompatible(CallingConv::ID CalleeCC,
260                                 CallingConv::ID CallerCC, MachineFunction &MF,
261                                 LLVMContext &C,
262                                 const SmallVectorImpl<ISD::InputArg> &Ins,
263                                 CCAssignFn CalleeFn, CCAssignFn CallerFn) {
264   if (CalleeCC == CallerCC)
265     return true;
266   SmallVector<CCValAssign, 4> RVLocs1;
267   CCState CCInfo1(CalleeCC, false, MF, RVLocs1, C);
268   CCInfo1.AnalyzeCallResult(Ins, CalleeFn);
269 
270   SmallVector<CCValAssign, 4> RVLocs2;
271   CCState CCInfo2(CallerCC, false, MF, RVLocs2, C);
272   CCInfo2.AnalyzeCallResult(Ins, CallerFn);
273 
274   if (RVLocs1.size() != RVLocs2.size())
275     return false;
276   for (unsigned I = 0, E = RVLocs1.size(); I != E; ++I) {
277     const CCValAssign &Loc1 = RVLocs1[I];
278     const CCValAssign &Loc2 = RVLocs2[I];
279     if (Loc1.getLocInfo() != Loc2.getLocInfo())
280       return false;
281     bool RegLoc1 = Loc1.isRegLoc();
282     if (RegLoc1 != Loc2.isRegLoc())
283       return false;
284     if (RegLoc1) {
285       if (Loc1.getLocReg() != Loc2.getLocReg())
286         return false;
287     } else {
288       if (Loc1.getLocMemOffset() != Loc2.getLocMemOffset())
289         return false;
290     }
291   }
292   return true;
293 }
294