Make structs readonly when applicable (#4002)

* Make all structs readonly when applicable. It should reduce amount of needless defensive copies

* Make structs with trivial boilerplate equality code record structs

* Remove unnecessary readonly modifiers from TextureCreateInfo

* Make BitMap structs readonly too

ARMeilleure/CodeGen/RegisterAllocators/AllocationResult.cs

@@ -1,6 +1,6 @@
 namespace ARMeilleure.CodeGen.RegisterAllocators
 {
-    struct AllocationResult
+    readonly struct AllocationResult
     {
         public int IntUsedRegisters { get; }
         public int VecUsedRegisters { get; }

ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs

@@ -11,7 +11,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
     {
         private class ParallelCopy
         {
-            private struct Copy
+            private readonly struct Copy
             {
                 public Register Dest   { get; }
                 public Register Source { get; }

ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs

@@ -11,7 +11,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 {
     class HybridAllocator : IRegisterAllocator
     {
-        private struct BlockInfo
+        private readonly struct BlockInfo
         {
             public bool HasCall { get; }
 

ARMeilleure/CodeGen/RegisterAllocators/RegisterMasks.cs

@@ -3,7 +3,7 @@ using System;
 
 namespace ARMeilleure.CodeGen.RegisterAllocators
 {
-    struct RegisterMasks
+    readonly struct RegisterMasks
     {
         public int IntAvailableRegisters   { get; }
         public int VecAvailableRegisters   { get; }

ARMeilleure/CodeGen/X86/IntrinsicInfo.cs

@@ -1,6 +1,6 @@
 namespace ARMeilleure.CodeGen.X86
 {
-    struct IntrinsicInfo
+    readonly struct IntrinsicInfo
     {
         public X86Instruction Inst { get; }
         public IntrinsicType  Type { get; }

ARMeilleure/Decoders/InstDescriptor.cs

@@ -2,7 +2,7 @@ using ARMeilleure.Instructions;
 
 namespace ARMeilleure.Decoders
 {
-    struct InstDescriptor
+    readonly struct InstDescriptor
     {
         public static InstDescriptor Undefined => new InstDescriptor(InstName.Und, InstEmit.Und);
 

ARMeilleure/Decoders/OpCodeTable.cs

@@ -11,7 +11,7 @@ namespace ARMeilleure.Decoders
 
         private const int FastLookupSize = 0x1000;
 
-        private struct InstInfo
+        private readonly struct InstInfo
         {
             public int Mask  { get; }
             public int Value { get; }

ARMeilleure/Diagnostics/Symbols.cs

@@ -6,7 +6,7 @@ namespace ARMeilleure.Diagnostics
 {
     static class Symbols
     {
-        private struct RangedSymbol
+        private readonly struct RangedSymbol
         {
             public readonly ulong Start;
             public readonly ulong End;

ARMeilleure/IntermediateRepresentation/PhiOperation.cs

@@ -3,7 +3,7 @@ using static ARMeilleure.IntermediateRepresentation.Operand.Factory;
 
 namespace ARMeilleure.IntermediateRepresentation
 {
-    struct PhiOperation
+    readonly struct PhiOperation
     {
         private readonly Operation _operation;
 

ARMeilleure/IntermediateRepresentation/Register.cs

@@ -2,7 +2,7 @@ using System;
 
 namespace ARMeilleure.IntermediateRepresentation
 {
-    struct Register : IEquatable<Register>
+    readonly struct Register : IEquatable<Register>
     {
         public int Index { get; }
 

ARMeilleure/Translation/Cache/CacheEntry.cs

@@ -4,7 +4,7 @@ using System.Diagnostics.CodeAnalysis;
 
 namespace ARMeilleure.Translation.Cache
 {
-    struct CacheEntry : IComparable<CacheEntry>
+    readonly struct CacheEntry : IComparable<CacheEntry>
     {
         public int Offset { get; }
         public int Size   { get; }

ARMeilleure/Translation/Cache/CacheMemoryAllocator.cs

@@ -6,7 +6,7 @@ namespace ARMeilleure.Translation.Cache
 {
     class CacheMemoryAllocator
     {
-        private struct MemoryBlock : IComparable<MemoryBlock>
+        private readonly struct MemoryBlock : IComparable<MemoryBlock>
         {
             public int Offset { get; }
             public int Size { get; }

ARMeilleure/Translation/CompilerContext.cs

@@ -2,7 +2,7 @@ using ARMeilleure.IntermediateRepresentation;
 
 namespace ARMeilleure.Translation
 {
-    struct CompilerContext
+    readonly struct CompilerContext
     {
         public ControlFlowGraph Cfg { get; }
 

ARMeilleure/Translation/RegisterUsage.cs

@@ -14,7 +14,7 @@ namespace ARMeilleure.Translation
         private const int RegsCount = 32;
         private const int RegsMask  = RegsCount - 1;
 
-        private struct RegisterMask : IEquatable<RegisterMask>
+        private readonly struct RegisterMask : IEquatable<RegisterMask>
         {
             public long IntMask => Mask.GetElement(0);
             public long VecMask => Mask.GetElement(1);

ARMeilleure/Translation/Translator.cs

@@ -293,7 +293,7 @@ namespace ARMeilleure.Translation
             }
         }
 
-        private struct Range
+        private readonly struct Range
         {
             public ulong Start { get; }
             public ulong End { get; }