Reduce allocations for Spir-v serialization

Passes BinaryWriter instead of the stream to Write and WriteOperand

- Removes creation of BinaryWriter for each instruction
- Removes allocations for literal string

Spv.Generator/Instruction.cs

@@ -111,15 +111,13 @@ namespace Spv.Generator
             AddOperand(LiteralInteger.CreateForEnum(value));
         }
 
-        public void Write(Stream stream)
+        public void Write(BinaryWriter writer)
         {
-            BinaryWriter writer = new BinaryWriter(stream);
-
             // Word 0
             writer.Write((ushort)Opcode);
             writer.Write(GetTotalWordCount());
 
-            _resultType?.WriteOperand(stream);
+            _resultType?.WriteOperand(writer);
 
             if (Id != InvalidId)
             {
@@ -128,11 +126,11 @@ namespace Spv.Generator
 
             foreach (Operand operand in _operands)
             {
-                operand.WriteOperand(stream);
+                operand.WriteOperand(writer);
             }
         }
 
-        public void WriteOperand(Stream stream)
+        public void WriteOperand(BinaryWriter writer)
         {
             Debug.Assert(Id != InvalidId);
 
@@ -156,7 +154,7 @@ namespace Spv.Generator
                 throw new InvalidOperationException($"Id wasn't bound to the module, please make sure to call {methodToCall}");
             }
 
-            stream.Write(BitConverter.GetBytes(Id));
+            writer.Write(Id);
         }
 
         public override bool Equals(object obj)

Spv.Generator/LiteralInteger.cs

@@ -53,9 +53,9 @@ namespace Spv.Generator
 
         public ushort WordCount => (ushort)(_data.Length / 4);
 
-        public void WriteOperand(Stream stream)
+        public void WriteOperand(BinaryWriter writer)
         {
-            stream.Write(_data);
+            writer.Write(_data);
         }
 
         public override bool Equals(object obj)

Spv.Generator/LiteralString.cs

@@ -17,15 +17,15 @@ namespace Spv.Generator
 
         public ushort WordCount => (ushort)(_value.Length / 4 + 1);
 
-        public void WriteOperand(Stream stream)
+        public void WriteOperand(BinaryWriter writer)
         {
-            byte[] rawValue = Encoding.ASCII.GetBytes(_value);
+            writer.Write(_value.AsSpan());
 
-            stream.Write(rawValue);
+            int paddingSize = 4 - (Encoding.ASCII.GetByteCount(_value) % 4);
 
-            int paddingSize = 4 - (rawValue.Length % 4);
+            Span<byte> padding = stackalloc byte[paddingSize];
 
-            stream.Write(new byte[paddingSize]);
+            writer.Write(padding);
         }
 
         public override bool Equals(object obj)

Spv.Generator/Module.cs

@@ -247,7 +247,7 @@ namespace Spv.Generator
         {
             using (MemoryStream stream = new MemoryStream())
             {
-                BinaryWriter writer = new BinaryWriter(stream);
+                BinaryWriter writer = new BinaryWriter(stream, System.Text.Encoding.ASCII);
 
                 // Header
                 writer.Write(MagicNumber);
@@ -262,7 +262,7 @@ namespace Spv.Generator
                     Instruction capabilityInstruction = new Instruction(Op.OpCapability);
 
                     capabilityInstruction.AddOperand(capability);
-                    capabilityInstruction.Write(stream);
+                    capabilityInstruction.Write(writer);
                 }
 
                 // 2.
@@ -271,44 +271,44 @@ namespace Spv.Generator
                     Instruction extensionInstruction = new Instruction(Op.OpExtension);
 
                     extensionInstruction.AddOperand(extension);
-                    extensionInstruction.Write(stream);
+                    extensionInstruction.Write(writer);
                 }
 
                 // 3.
                 foreach (Instruction extInstImport in _extInstImports)
                 {
-                    extInstImport.Write(stream);
+                    extInstImport.Write(writer);
                 }
 
                 // 4.
                 Instruction memoryModelInstruction = new Instruction(Op.OpMemoryModel);
                 memoryModelInstruction.AddOperand(_addressingModel);
                 memoryModelInstruction.AddOperand(_memoryModel);
-                memoryModelInstruction.Write(stream);
+                memoryModelInstruction.Write(writer);
 
                 // 5.
                 foreach (Instruction entrypoint in _entrypoints)
                 {
-                    entrypoint.Write(stream);
+                    entrypoint.Write(writer);
                 }
 
                 // 6.
                 foreach (Instruction executionMode in _executionModes)
                 {
-                    executionMode.Write(stream);
+                    executionMode.Write(writer);
                 }
 
                 // 7.
                 // TODO: order debug information correclty.
                 foreach (Instruction debug in _debug)
                 {
-                    debug.Write(stream);
+                    debug.Write(writer);
                 }
 
                 // 8.
                 foreach (Instruction annotation in _annotations)
                 {
-                    annotation.Write(stream);
+                    annotation.Write(writer);
                 }
 
                 // Ensure that everything is in the right order in the declarations section
@@ -320,19 +320,19 @@ namespace Spv.Generator
                 // 9.
                 foreach (Instruction declaration in declarations)
                 {
-                    declaration.Write(stream);
+                    declaration.Write(writer);
                 }
 
                 // 10.
                 foreach (Instruction functionDeclaration in _functionsDeclarations)
                 {
-                    functionDeclaration.Write(stream);
+                    functionDeclaration.Write(writer);
                 }
 
                 // 11.
                 foreach (Instruction functionDefinition in _functionsDefinitions)
                 {
-                    functionDefinition.Write(stream);
+                    functionDefinition.Write(writer);
                 }
 
                 return stream.ToArray();

Spv.Generator/Operand.cs

@@ -9,6 +9,6 @@ namespace Spv.Generator
 
         ushort WordCount { get; }
 
-        void WriteOperand(Stream stream);
+        void WriteOperand(BinaryWriter writer);
     }
 }