Refactor `PtcInfo` (#2625)

* Refactor `PtcInfo`

This change reduces the coupling of `PtcInfo` by moving relocation
tracking to the backend. `RelocEntry`s remains as `RelocEntry`s through
out the pipeline until it actually needs to be written to the PTC
streams. Keeping this representation makes inspecting and manipulating
relocations after compilations less painful. This is something I needed
to do to patch relocations to 0 to diff dumps.

Contributes to #1125.

* Turn `Symbol` & `RelocInfo` into readonly structs

* Add documentation to `CompiledFunction`

* Remove `Compiler.Compile<T>`

Remove `Compiler.Compile<T>` and replace it by `Map<T>` of the
`CompiledFunction` returned.

4 files changed, 198 insertions, 0 deletions

diff --git a/ARMeilleure/CodeGen/Linking/RelocEntry.cs b/ARMeilleure/CodeGen/Linking/RelocEntry.cs
new file mode 100644
index 00000000..a27bfded
--- /dev/null
+++ b/ARMeilleure/CodeGen/Linking/RelocEntry.cs
@@ -0,0 +1,38 @@
+namespace ARMeilleure.CodeGen.Linking
+{
+    /// <summary>
+    /// Represents a relocation.
+    /// </summary>
+    readonly struct RelocEntry
+    {
+        public const int Stride = 13; // Bytes.
+
+        /// <summary>
+        /// Gets the position of the relocation.
+        /// </summary>
+        public int Position { get; }
+
+        /// <summary>
+        /// Gets the <see cref="Symbol"/> of the relocation.
+        /// </summary>
+        public Symbol Symbol { get; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RelocEntry"/> struct with the specified position and
+        /// <see cref="Symbol"/>.
+        /// </summary>
+        /// <param name="position">Position of relocation</param>
+        /// <param name="symbol">Symbol of relocation</param>
+        public RelocEntry(int position, Symbol symbol)
+        {
+            Position = position;
+            Symbol = symbol;
+        }
+
+        /// <inheritdoc/>
+        public override string ToString()
+        {
+            return $"({nameof(Position)} = {Position}, {nameof(Symbol)} = {Symbol})";
+        }
+    }
+}
\ No newline at end of file
diff --git a/ARMeilleure/CodeGen/Linking/RelocInfo.cs b/ARMeilleure/CodeGen/Linking/RelocInfo.cs
new file mode 100644
index 00000000..922b8bfe
--- /dev/null
+++ b/ARMeilleure/CodeGen/Linking/RelocInfo.cs
@@ -0,0 +1,32 @@
+using System;
+
+namespace ARMeilleure.CodeGen.Linking
+{
+    /// <summary>
+    /// Represents relocation information about a <see cref="CompiledFunction"/>.
+    /// </summary>
+    readonly struct RelocInfo
+    {
+        /// <summary>
+        /// Gets an empty <see cref="RelocInfo"/>.
+        /// </summary>
+        public static RelocInfo Empty { get; } = new RelocInfo(null);
+
+        private readonly RelocEntry[] _entries;
+
+        /// <summary>
+        /// Gets the set of <see cref="RelocEntry"/>.
+        /// </summary>
+        public ReadOnlySpan<RelocEntry> Entries => _entries ?? Array.Empty<RelocEntry>();
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RelocInfo"/> struct with the specified set of
+        /// <see cref="RelocEntry"/>.
+        /// </summary>
+        /// <param name="entries">Set of <see cref="RelocInfo"/> to use</param>
+        public RelocInfo(RelocEntry[] entries)
+        {
+            _entries = entries ?? Array.Empty<RelocEntry>();
+        }
+    }
+}
\ No newline at end of file
diff --git a/ARMeilleure/CodeGen/Linking/Symbol.cs b/ARMeilleure/CodeGen/Linking/Symbol.cs
new file mode 100644
index 00000000..fa47ee23
--- /dev/null
+++ b/ARMeilleure/CodeGen/Linking/Symbol.cs
@@ -0,0 +1,100 @@
+using System;
+
+namespace ARMeilleure.CodeGen.Linking
+{
+    /// <summary>
+    /// Represents a symbol.
+    /// </summary>
+    readonly struct Symbol
+    {
+        private readonly ulong _value;
+
+        /// <summary>
+        /// Gets the <see cref="SymbolType"/> of the <see cref="Symbol"/>.
+        /// </summary>
+        public SymbolType Type { get; }
+
+        /// <summary>
+        /// Gets the value of the <see cref="Symbol"/>.
+        /// </summary>
+        /// <exception cref="InvalidOperationException"><see cref="Type"/> is <see cref="SymbolType.None"/></exception>
+        public ulong Value
+        {
+            get
+            {
+                if (Type == SymbolType.None)
+                {
+                    ThrowSymbolNone();
+                }
+
+                return _value;
+            }
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Symbol"/> structure with the specified <see cref="SymbolType"/> and value.
+        /// </summary>
+        /// <param name="type">Type of symbol</param>
+        /// <param name="value">Value of symbol</param>
+        public Symbol(SymbolType type, ulong value)
+        {
+            (Type, _value) = (type, value);
+        }
+
+        /// <summary>
+        /// Determines if the specified <see cref="Symbol"/> instances are equal.
+        /// </summary>
+        /// <param name="a">First instance</param>
+        /// <param name="b">Second instance</param>
+        /// <returns><see langword="true"/> if equal; otherwise <see langword="false"/></returns>
+        public static bool operator ==(Symbol a, Symbol b)
+        {
+            return a.Equals(b);
+        }
+
+        /// <summary>
+        /// Determines if the specified <see cref="Symbol"/> instances are not equal.
+        /// </summary>
+        /// <param name="a">First instance</param>
+        /// <param name="b">Second instance</param>
+        /// <returns><see langword="true"/> if not equal; otherwise <see langword="false"/></returns>
+        /// <inheritdoc/>
+        public static bool operator !=(Symbol a, Symbol b)
+        {
+            return !(a == b);
+        }
+
+        /// <summary>
+        /// Determines if the specified <see cref="Symbol"/> is equal to this <see cref="Symbol"/> instance.
+        /// </summary>
+        /// <param name="other">Other <see cref="Symbol"/> instance</param>
+        /// <returns><see langword="true"/> if equal; otherwise <see langword="false"/></returns>
+        public bool Equals(Symbol other)
+        {
+            return other.Type == Type && other._value == _value;
+        }
+
+        /// <inheritdoc/>
+        public override bool Equals(object obj)
+        {
+            return obj is Symbol sym && Equals(sym);
+        }
+
+        /// <inheritdoc/>
+        public override int GetHashCode()
+        {
+            return HashCode.Combine(Type, _value);
+        }
+
+        /// <inheritdoc/>
+        public override string ToString()
+        {
+            return $"{Type}:{_value}";
+        }
+
+        private static void ThrowSymbolNone()
+        {
+            throw new InvalidOperationException("Symbol refers to nothing.");
+        }
+    }
+}
diff --git a/ARMeilleure/CodeGen/Linking/SymbolType.cs b/ARMeilleure/CodeGen/Linking/SymbolType.cs
new file mode 100644
index 00000000..b05b6969
--- /dev/null
+++ b/ARMeilleure/CodeGen/Linking/SymbolType.cs
@@ -0,0 +1,28 @@
+namespace ARMeilleure.CodeGen.Linking
+{
+    /// <summary>
+    /// Types of <see cref="Symbol"/>.
+    /// </summary>
+    enum SymbolType : byte
+    {
+        /// <summary>
+        /// Refers to nothing, i.e no symbol.
+        /// </summary>
+        None,
+
+        /// <summary>
+        /// Refers to an entry in <see cref="Translation.Delegates"/>.
+        /// </summary>
+        DelegateTable,
+
+        /// <summary>
+        /// Refers to an entry in <see cref="Translation.Translator.FunctionTable"/>.
+        /// </summary>
+        FunctionTable,
+
+        /// <summary>
+        /// Refers to a special symbol which is handled by <see cref="Translation.PTC.Ptc.PatchCode"/>.
+        /// </summary>
+        Special
+    }
+}