1 //===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file is a copy of the generic LLVM PrologEpilogInserter pass, modified
11 // to remove unneeded functionality and to handle virtual registers. Most code
12 // here is a copy of PrologEpilogInserter.cpp.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "NVPTX.h"
17 #include "llvm/CodeGen/MachineFrameInfo.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/Pass.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/raw_ostream.h"
23 #include "llvm/Target/TargetFrameLowering.h"
24 #include "llvm/Target/TargetRegisterInfo.h"
25 #include "llvm/Target/TargetSubtargetInfo.h"
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "nvptx-prolog-epilog"
30
31 namespace {
32 class NVPTXPrologEpilogPass : public MachineFunctionPass {
33 public:
34 static char ID;
NVPTXPrologEpilogPass()35 NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
36
37 bool runOnMachineFunction(MachineFunction &MF) override;
38
39 private:
40 void calculateFrameObjectOffsets(MachineFunction &Fn);
41 };
42 }
43
createNVPTXPrologEpilogPass()44 MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
45 return new NVPTXPrologEpilogPass();
46 }
47
48 char NVPTXPrologEpilogPass::ID = 0;
49
runOnMachineFunction(MachineFunction & MF)50 bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
51 const TargetSubtargetInfo &STI = MF.getSubtarget();
52 const TargetFrameLowering &TFI = *STI.getFrameLowering();
53 const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
54 bool Modified = false;
55
56 calculateFrameObjectOffsets(MF);
57
58 for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB) {
59 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
60 MachineInstr *MI = I;
61 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
62 if (!MI->getOperand(i).isFI())
63 continue;
64 TRI.eliminateFrameIndex(MI, 0, i, nullptr);
65 Modified = true;
66 }
67 }
68 }
69
70 // Add function prolog/epilog
71 TFI.emitPrologue(MF);
72
73 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
74 // If last instruction is a return instruction, add an epilogue
75 if (!I->empty() && I->back().isReturn())
76 TFI.emitEpilogue(MF, *I);
77 }
78
79 return Modified;
80 }
81
82 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
83 static inline void
AdjustStackOffset(MachineFrameInfo * MFI,int FrameIdx,bool StackGrowsDown,int64_t & Offset,unsigned & MaxAlign)84 AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
85 bool StackGrowsDown, int64_t &Offset,
86 unsigned &MaxAlign) {
87 // If the stack grows down, add the object size to find the lowest address.
88 if (StackGrowsDown)
89 Offset += MFI->getObjectSize(FrameIdx);
90
91 unsigned Align = MFI->getObjectAlignment(FrameIdx);
92
93 // If the alignment of this object is greater than that of the stack, then
94 // increase the stack alignment to match.
95 MaxAlign = std::max(MaxAlign, Align);
96
97 // Adjust to alignment boundary.
98 Offset = (Offset + Align - 1) / Align * Align;
99
100 if (StackGrowsDown) {
101 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
102 MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
103 } else {
104 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
105 MFI->setObjectOffset(FrameIdx, Offset);
106 Offset += MFI->getObjectSize(FrameIdx);
107 }
108 }
109
110 void
calculateFrameObjectOffsets(MachineFunction & Fn)111 NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
112 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
113 const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
114
115 bool StackGrowsDown =
116 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
117
118 // Loop over all of the stack objects, assigning sequential addresses...
119 MachineFrameInfo *MFI = Fn.getFrameInfo();
120
121 // Start at the beginning of the local area.
122 // The Offset is the distance from the stack top in the direction
123 // of stack growth -- so it's always nonnegative.
124 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
125 if (StackGrowsDown)
126 LocalAreaOffset = -LocalAreaOffset;
127 assert(LocalAreaOffset >= 0
128 && "Local area offset should be in direction of stack growth");
129 int64_t Offset = LocalAreaOffset;
130
131 // If there are fixed sized objects that are preallocated in the local area,
132 // non-fixed objects can't be allocated right at the start of local area.
133 // We currently don't support filling in holes in between fixed sized
134 // objects, so we adjust 'Offset' to point to the end of last fixed sized
135 // preallocated object.
136 for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
137 int64_t FixedOff;
138 if (StackGrowsDown) {
139 // The maximum distance from the stack pointer is at lower address of
140 // the object -- which is given by offset. For down growing stack
141 // the offset is negative, so we negate the offset to get the distance.
142 FixedOff = -MFI->getObjectOffset(i);
143 } else {
144 // The maximum distance from the start pointer is at the upper
145 // address of the object.
146 FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
147 }
148 if (FixedOff > Offset) Offset = FixedOff;
149 }
150
151 // NOTE: We do not have a call stack
152
153 unsigned MaxAlign = MFI->getMaxAlignment();
154
155 // No scavenger
156
157 // FIXME: Once this is working, then enable flag will change to a target
158 // check for whether the frame is large enough to want to use virtual
159 // frame index registers. Functions which don't want/need this optimization
160 // will continue to use the existing code path.
161 if (MFI->getUseLocalStackAllocationBlock()) {
162 unsigned Align = MFI->getLocalFrameMaxAlign();
163
164 // Adjust to alignment boundary.
165 Offset = (Offset + Align - 1) / Align * Align;
166
167 DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
168
169 // Resolve offsets for objects in the local block.
170 for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
171 std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
172 int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
173 DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
174 FIOffset << "]\n");
175 MFI->setObjectOffset(Entry.first, FIOffset);
176 }
177 // Allocate the local block
178 Offset += MFI->getLocalFrameSize();
179
180 MaxAlign = std::max(Align, MaxAlign);
181 }
182
183 // No stack protector
184
185 // Then assign frame offsets to stack objects that are not used to spill
186 // callee saved registers.
187 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
188 if (MFI->isObjectPreAllocated(i) &&
189 MFI->getUseLocalStackAllocationBlock())
190 continue;
191 if (MFI->isDeadObjectIndex(i))
192 continue;
193
194 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
195 }
196
197 // No scavenger
198
199 if (!TFI.targetHandlesStackFrameRounding()) {
200 // If we have reserved argument space for call sites in the function
201 // immediately on entry to the current function, count it as part of the
202 // overall stack size.
203 if (MFI->adjustsStack() && TFI.hasReservedCallFrame(Fn))
204 Offset += MFI->getMaxCallFrameSize();
205
206 // Round up the size to a multiple of the alignment. If the function has
207 // any calls or alloca's, align to the target's StackAlignment value to
208 // ensure that the callee's frame or the alloca data is suitably aligned;
209 // otherwise, for leaf functions, align to the TransientStackAlignment
210 // value.
211 unsigned StackAlign;
212 if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
213 (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
214 StackAlign = TFI.getStackAlignment();
215 else
216 StackAlign = TFI.getTransientStackAlignment();
217
218 // If the frame pointer is eliminated, all frame offsets will be relative to
219 // SP not FP. Align to MaxAlign so this works.
220 StackAlign = std::max(StackAlign, MaxAlign);
221 unsigned AlignMask = StackAlign - 1;
222 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
223 }
224
225 // Update frame info to pretend that this is part of the stack...
226 int64_t StackSize = Offset - LocalAreaOffset;
227 MFI->setStackSize(StackSize);
228 }
229