1 //===-- LiveStacks.cpp - Live Stack Slot Analysis -------------------------===//
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 live stack slot analysis pass. It is analogous to
10 // live interval analysis except it's analyzing liveness of stack slots rather
11 // than registers.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/CodeGen/LiveStacks.h"
16 #include "llvm/CodeGen/TargetRegisterInfo.h"
17 #include "llvm/CodeGen/TargetSubtargetInfo.h"
18 #include "llvm/InitializePasses.h"
19 using namespace llvm;
20 
21 #define DEBUG_TYPE "livestacks"
22 
23 char LiveStacks::ID = 0;
24 INITIALIZE_PASS_BEGIN(LiveStacks, DEBUG_TYPE,
25                 "Live Stack Slot Analysis", false, false)
26 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
27 INITIALIZE_PASS_END(LiveStacks, DEBUG_TYPE,
28                 "Live Stack Slot Analysis", false, false)
29 
30 char &llvm::LiveStacksID = LiveStacks::ID;
31 
32 void LiveStacks::getAnalysisUsage(AnalysisUsage &AU) const {
33   AU.setPreservesAll();
34   AU.addPreserved<SlotIndexes>();
35   AU.addRequiredTransitive<SlotIndexes>();
36   MachineFunctionPass::getAnalysisUsage(AU);
37 }
38 
39 void LiveStacks::releaseMemory() {
40   // Release VNInfo memory regions, VNInfo objects don't need to be dtor'd.
41   VNInfoAllocator.Reset();
42   S2IMap.clear();
43   S2RCMap.clear();
44 }
45 
46 bool LiveStacks::runOnMachineFunction(MachineFunction &MF) {
47   TRI = MF.getSubtarget().getRegisterInfo();
48   // FIXME: No analysis is being done right now. We are relying on the
49   // register allocators to provide the information.
50   return false;
51 }
52 
53 LiveInterval &
54 LiveStacks::getOrCreateInterval(int Slot, const TargetRegisterClass *RC) {
55   assert(Slot >= 0 && "Spill slot indice must be >= 0");
56   SS2IntervalMap::iterator I = S2IMap.find(Slot);
57   if (I == S2IMap.end()) {
58     I = S2IMap
59             .emplace(
60                 std::piecewise_construct, std::forward_as_tuple(Slot),
61                 std::forward_as_tuple(Register::index2StackSlot(Slot), 0.0F))
62             .first;
63     S2RCMap.insert(std::make_pair(Slot, RC));
64   } else {
65     // Use the largest common subclass register class.
66     const TargetRegisterClass *OldRC = S2RCMap[Slot];
67     S2RCMap[Slot] = TRI->getCommonSubClass(OldRC, RC);
68   }
69   return I->second;
70 }
71 
72 /// print - Implement the dump method.
73 void LiveStacks::print(raw_ostream &OS, const Module*) const {
74 
75   OS << "********** INTERVALS **********\n";
76   for (const_iterator I = begin(), E = end(); I != E; ++I) {
77     I->second.print(OS);
78     int Slot = I->first;
79     const TargetRegisterClass *RC = getIntervalRegClass(Slot);
80     if (RC)
81       OS << " [" << TRI->getRegClassName(RC) << "]\n";
82     else
83       OS << " [Unknown]\n";
84   }
85 }
86