1 //===- ConstantPools.h - Keep track of assembler-generated ------*- C++ -*-===//
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 declares the ConstantPool and AssemblerConstantPools classes.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_MC_CONSTANTPOOLS_H
14 #define LLVM_MC_CONSTANTPOOLS_H
15 
16 #include "llvm/ADT/MapVector.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/Support/SMLoc.h"
19 #include <cstdint>
20 #include <map>
21 
22 namespace llvm {
23 
24 class MCContext;
25 class MCExpr;
26 class MCSection;
27 class MCStreamer;
28 class MCSymbol;
29 class MCSymbolRefExpr;
30 
31 struct ConstantPoolEntry {
ConstantPoolEntryConstantPoolEntry32   ConstantPoolEntry(MCSymbol *L, const MCExpr *Val, unsigned Sz, SMLoc Loc_)
33     : Label(L), Value(Val), Size(Sz), Loc(Loc_) {}
34 
35   MCSymbol *Label;
36   const MCExpr *Value;
37   unsigned Size;
38   SMLoc Loc;
39 };
40 
41 // A class to keep track of assembler-generated constant pools that are use to
42 // implement the ldr-pseudo.
43 class ConstantPool {
44   using EntryVecTy = SmallVector<ConstantPoolEntry, 4>;
45   EntryVecTy Entries;
46   std::map<int64_t, const MCSymbolRefExpr *> CachedEntries;
47 
48 public:
49   // Initialize a new empty constant pool
50   ConstantPool() = default;
51 
52   // Add a new entry to the constant pool in the next slot.
53   // \param Value is the new entry to put in the constant pool.
54   // \param Size is the size in bytes of the entry
55   //
56   // \returns a MCExpr that references the newly inserted value
57   const MCExpr *addEntry(const MCExpr *Value, MCContext &Context,
58                          unsigned Size, SMLoc Loc);
59 
60   // Emit the contents of the constant pool using the provided streamer.
61   void emitEntries(MCStreamer &Streamer);
62 
63   // Return true if the constant pool is empty
64   bool empty();
65 
66   void clearCache();
67 };
68 
69 class AssemblerConstantPools {
70   // Map type used to keep track of per-Section constant pools used by the
71   // ldr-pseudo opcode. The map associates a section to its constant pool. The
72   // constant pool is a vector of (label, value) pairs. When the ldr
73   // pseudo is parsed we insert a new (label, value) pair into the constant pool
74   // for the current section and add MCSymbolRefExpr to the new label as
75   // an opcode to the ldr. After we have parsed all the user input we
76   // output the (label, value) pairs in each constant pool at the end of the
77   // section.
78   //
79   // We use the MapVector for the map type to ensure stable iteration of
80   // the sections at the end of the parse. We need to iterate over the
81   // sections in a stable order to ensure that we have print the
82   // constant pools in a deterministic order when printing an assembly
83   // file.
84   using ConstantPoolMapTy = MapVector<MCSection *, ConstantPool>;
85   ConstantPoolMapTy ConstantPools;
86 
87 public:
88   void emitAll(MCStreamer &Streamer);
89   void emitForCurrentSection(MCStreamer &Streamer);
90   void clearCacheForCurrentSection(MCStreamer &Streamer);
91   const MCExpr *addEntry(MCStreamer &Streamer, const MCExpr *Expr,
92                          unsigned Size, SMLoc Loc);
93 
94 private:
95   ConstantPool *getConstantPool(MCSection *Section);
96   ConstantPool &getOrCreateConstantPool(MCSection *Section);
97 };
98 
99 } // end namespace llvm
100 
101 #endif // LLVM_MC_CONSTANTPOOLS_H
102