1//===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
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 is a copy of the generic LLVM PrologEpilogInserter pass, modified
10// to remove unneeded functionality and to handle virtual registers. Most code
11// here is a copy of PrologEpilogInserter.cpp.
12//
13//===----------------------------------------------------------------------===//
14
15#include "NVPTX.h"
16#include "llvm/CodeGen/MachineFrameInfo.h"
17#include "llvm/CodeGen/MachineFunction.h"
18#include "llvm/CodeGen/MachineFunctionPass.h"
19#include "llvm/CodeGen/TargetFrameLowering.h"
20#include "llvm/CodeGen/TargetRegisterInfo.h"
21#include "llvm/CodeGen/TargetSubtargetInfo.h"
22#include "llvm/IR/DebugInfoMetadata.h"
23#include "llvm/Pass.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/raw_ostream.h"
26
27using namespace llvm;
28
29#define DEBUG_TYPE "nvptx-prolog-epilog"
30
31namespace {
32class NVPTXPrologEpilogPass : public MachineFunctionPass {
33public:
34 static char ID;
35 NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
36
37 bool runOnMachineFunction(MachineFunction &MF) override;
38
39 StringRef getPassName() const override { return "NVPTX Prolog Epilog Pass"; }
40
41private:
42 void calculateFrameObjectOffsets(MachineFunction &Fn);
43};
44} // end anonymous namespace
45
46MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
47 return new NVPTXPrologEpilogPass();
48}
49
50char NVPTXPrologEpilogPass::ID = 0;
51
52INITIALIZE_PASS(NVPTXPrologEpilogPass, DEBUG_TYPE,
53 "NVPTX Prologue/Epilogue Insertion", false, false)
54
55static bool replaceFrameIndexDebugInstr(MachineFunction &MF, MachineInstr &MI,
56 unsigned OpIdx) {
57 const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
58 const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
59 if (MI.isDebugValue()) {
60
61 MachineOperand &Op = MI.getOperand(i: OpIdx);
62 assert(MI.isDebugOperand(&Op) &&
63 "Frame indices can only appear as a debug operand in a DBG_VALUE*"
64 " machine instruction");
65 Register Reg;
66 unsigned FrameIdx = Op.getIndex();
67
68 StackOffset Offset = TFI->getFrameIndexReference(MF, FI: FrameIdx, FrameReg&: Reg);
69 Op.ChangeToRegister(Reg, isDef: false /*isDef*/);
70
71 const DIExpression *DIExpr = MI.getDebugExpression();
72 if (MI.isNonListDebugValue()) {
73 DIExpr = TRI.prependOffsetExpression(Expr: MI.getDebugExpression(),
74 PrependFlags: DIExpression::ApplyOffset, Offset);
75 } else {
76 // The debug operand at DebugOpIndex was a frame index at offset
77 // `Offset`; now the operand has been replaced with the frame
78 // register, we must add Offset with `register x, plus Offset`.
79 unsigned DebugOpIndex = MI.getDebugOperandIndex(Op: &Op);
80 SmallVector<uint64_t, 3> Ops;
81 TRI.getOffsetOpcodes(Offset, Ops);
82 DIExpr = DIExpression::appendOpsToArg(Expr: DIExpr, Ops, ArgNo: DebugOpIndex);
83 }
84 MI.getDebugExpressionOp().setMetadata(DIExpr);
85 return true;
86 }
87 return false;
88}
89
90bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
91 const TargetSubtargetInfo &STI = MF.getSubtarget();
92 const TargetFrameLowering &TFI = *STI.getFrameLowering();
93 const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
94 bool Modified = false;
95
96 calculateFrameObjectOffsets(Fn&: MF);
97
98 for (MachineBasicBlock &BB : MF) {
99 for (MachineBasicBlock::iterator I = BB.end(); I != BB.begin();) {
100 MachineInstr &MI = *std::prev(x: I);
101
102 bool RemovedMI = false;
103 for (const auto &[Idx, Op] : enumerate(First: MI.operands())) {
104 if (!Op.isFI())
105 continue;
106
107 if (replaceFrameIndexDebugInstr(MF, MI, OpIdx: Idx))
108 continue;
109
110 // Eliminate this FrameIndex operand.
111 RemovedMI = TRI.eliminateFrameIndex(MI, SPAdj: 0, FIOperandNum: Idx, RS: nullptr);
112 Modified = true;
113 if (RemovedMI)
114 break;
115 }
116
117 if (!RemovedMI)
118 --I;
119 }
120 }
121
122 // Add function prolog/epilog
123 TFI.emitPrologue(MF, MBB&: MF.front());
124
125 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
126 // If last instruction is a return instruction, add an epilogue
127 if (I->isReturnBlock())
128 TFI.emitEpilogue(MF, MBB&: *I);
129 }
130
131 return Modified;
132}
133
134/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
135static inline void AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
136 bool StackGrowsDown, int64_t &Offset,
137 Align &MaxAlign) {
138 // If the stack grows down, add the object size to find the lowest address.
139 if (StackGrowsDown)
140 Offset += MFI.getObjectSize(ObjectIdx: FrameIdx);
141
142 Align Alignment = MFI.getObjectAlign(ObjectIdx: FrameIdx);
143
144 // If the alignment of this object is greater than that of the stack, then
145 // increase the stack alignment to match.
146 MaxAlign = std::max(a: MaxAlign, b: Alignment);
147
148 // Adjust to alignment boundary.
149 Offset = alignTo(Size: Offset, A: Alignment);
150
151 if (StackGrowsDown) {
152 LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset
153 << "]\n");
154 MFI.setObjectOffset(ObjectIdx: FrameIdx, SPOffset: -Offset); // Set the computed offset
155 } else {
156 LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset
157 << "]\n");
158 MFI.setObjectOffset(ObjectIdx: FrameIdx, SPOffset: Offset);
159 Offset += MFI.getObjectSize(ObjectIdx: FrameIdx);
160 }
161}
162
163void
164NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
165 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
166 const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
167
168 bool StackGrowsDown =
169 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
170
171 // Loop over all of the stack objects, assigning sequential addresses...
172 MachineFrameInfo &MFI = Fn.getFrameInfo();
173
174 // Start at the beginning of the local area.
175 // The Offset is the distance from the stack top in the direction
176 // of stack growth -- so it's always nonnegative.
177 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
178 if (StackGrowsDown)
179 LocalAreaOffset = -LocalAreaOffset;
180 assert(LocalAreaOffset >= 0
181 && "Local area offset should be in direction of stack growth");
182 int64_t Offset = LocalAreaOffset;
183
184 // If there are fixed sized objects that are preallocated in the local area,
185 // non-fixed objects can't be allocated right at the start of local area.
186 // We currently don't support filling in holes in between fixed sized
187 // objects, so we adjust 'Offset' to point to the end of last fixed sized
188 // preallocated object.
189 for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
190 int64_t FixedOff;
191 if (StackGrowsDown) {
192 // The maximum distance from the stack pointer is at lower address of
193 // the object -- which is given by offset. For down growing stack
194 // the offset is negative, so we negate the offset to get the distance.
195 FixedOff = -MFI.getObjectOffset(ObjectIdx: i);
196 } else {
197 // The maximum distance from the start pointer is at the upper
198 // address of the object.
199 FixedOff = MFI.getObjectOffset(ObjectIdx: i) + MFI.getObjectSize(ObjectIdx: i);
200 }
201 if (FixedOff > Offset) Offset = FixedOff;
202 }
203
204 // NOTE: We do not have a call stack
205
206 Align MaxAlign = MFI.getMaxAlign();
207
208 // No scavenger
209
210 // FIXME: Once this is working, then enable flag will change to a target
211 // check for whether the frame is large enough to want to use virtual
212 // frame index registers. Functions which don't want/need this optimization
213 // will continue to use the existing code path.
214 if (MFI.getUseLocalStackAllocationBlock()) {
215 Align Alignment = MFI.getLocalFrameMaxAlign();
216
217 // Adjust to alignment boundary.
218 Offset = alignTo(Size: Offset, A: Alignment);
219
220 LLVM_DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
221
222 // Resolve offsets for objects in the local block.
223 for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
224 std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
225 int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
226 LLVM_DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" << FIOffset
227 << "]\n");
228 MFI.setObjectOffset(ObjectIdx: Entry.first, SPOffset: FIOffset);
229 }
230 // Allocate the local block
231 Offset += MFI.getLocalFrameSize();
232
233 MaxAlign = std::max(a: Alignment, b: MaxAlign);
234 }
235
236 // No stack protector
237
238 // Then assign frame offsets to stack objects that are not used to spill
239 // callee saved registers.
240 for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
241 if (MFI.isObjectPreAllocated(ObjectIdx: i) &&
242 MFI.getUseLocalStackAllocationBlock())
243 continue;
244 if (MFI.isDeadObjectIndex(ObjectIdx: i))
245 continue;
246
247 AdjustStackOffset(MFI, FrameIdx: i, StackGrowsDown, Offset, MaxAlign);
248 }
249
250 // No scavenger
251
252 if (!TFI.targetHandlesStackFrameRounding()) {
253 // If we have reserved argument space for call sites in the function
254 // immediately on entry to the current function, count it as part of the
255 // overall stack size.
256 if (MFI.adjustsStack() && TFI.hasReservedCallFrame(MF: Fn))
257 Offset += MFI.getMaxCallFrameSize();
258
259 // Round up the size to a multiple of the alignment. If the function has
260 // any calls or alloca's, align to the target's StackAlignment value to
261 // ensure that the callee's frame or the alloca data is suitably aligned;
262 // otherwise, for leaf functions, align to the TransientStackAlignment
263 // value.
264 Align StackAlign;
265 if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
266 (RegInfo->hasStackRealignment(MF: Fn) && MFI.getObjectIndexEnd() != 0))
267 StackAlign = TFI.getStackAlign();
268 else
269 StackAlign = TFI.getTransientStackAlign();
270
271 // If the frame pointer is eliminated, all frame offsets will be relative to
272 // SP not FP. Align to MaxAlign so this works.
273 Offset = alignTo(Size: Offset, A: std::max(a: StackAlign, b: MaxAlign));
274 }
275
276 // Update frame info to pretend that this is part of the stack...
277 int64_t StackSize = Offset - LocalAreaOffset;
278 MFI.setStackSize(StackSize);
279}
280