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