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 *> CachedConstantEntries;
47   DenseMap<const MCSymbol *, const MCSymbolRefExpr *> CachedSymbolEntries;
48 
49 public:
50   // Initialize a new empty constant pool
51   ConstantPool() = default;
52 
53   // Add a new entry to the constant pool in the next slot.
54   // \param Value is the new entry to put in the constant pool.
55   // \param Size is the size in bytes of the entry
56   //
57   // \returns a MCExpr that references the newly inserted value
58   const MCExpr *addEntry(const MCExpr *Value, MCContext &Context,
59                          unsigned Size, SMLoc Loc);
60 
61   // Emit the contents of the constant pool using the provided streamer.
62   void emitEntries(MCStreamer &Streamer);
63 
64   // Return true if the constant pool is empty
65   bool empty();
66 
67   void clearCache();
68 };
69 
70 class AssemblerConstantPools {
71   // Map type used to keep track of per-Section constant pools used by the
72   // ldr-pseudo opcode. The map associates a section to its constant pool. The
73   // constant pool is a vector of (label, value) pairs. When the ldr
74   // pseudo is parsed we insert a new (label, value) pair into the constant pool
75   // for the current section and add MCSymbolRefExpr to the new label as
76   // an opcode to the ldr. After we have parsed all the user input we
77   // output the (label, value) pairs in each constant pool at the end of the
78   // section.
79   //
80   // We use the MapVector for the map type to ensure stable iteration of
81   // the sections at the end of the parse. We need to iterate over the
82   // sections in a stable order to ensure that we have print the
83   // constant pools in a deterministic order when printing an assembly
84   // file.
85   using ConstantPoolMapTy = MapVector<MCSection *, ConstantPool>;
86   ConstantPoolMapTy ConstantPools;
87 
88 public:
89   void emitAll(MCStreamer &Streamer);
90   void emitForCurrentSection(MCStreamer &Streamer);
91   void clearCacheForCurrentSection(MCStreamer &Streamer);
92   const MCExpr *addEntry(MCStreamer &Streamer, const MCExpr *Expr,
93                          unsigned Size, SMLoc Loc);
94 
95 private:
96   ConstantPool *getConstantPool(MCSection *Section);
97   ConstantPool &getOrCreateConstantPool(MCSection *Section);
98 };
99 
100 } // end namespace llvm
101 
102 #endif // LLVM_MC_CONSTANTPOOLS_H
103