WasmParser: Specialize more hot paths (#153)

With this change, we can achieve 17% speedup on stringify macro
benchmark. The performance number is same as the case with CMO but with
smaller binary size.

|            | baseline | CMO   | this change |
|------------|----------|-------|-------------|
| speed (ms) | 198.1    | 172.8 | 169.9       |
| size  (kb) [^1] | 1739     | 1923  | 1797        |

[^1]: swift-6.0.1-RELEASE, macOS 14.4.1 arm64

Author: kateinoigakukun

Sources/WasmParser/LEB.swift

@@ -1,10 +1,11 @@
+@usableFromInline
 enum LEBError: Swift.Error, Equatable {
     case overflow
     case integerRepresentationTooLong
     case insufficientBytes
 }
 
-@inline(__always)
+@inlinable
 func decodeLEB128<IntType, Stream>(
     stream: Stream
 ) throws -> IntType where IntType: FixedWidthInteger, IntType: UnsignedInteger, Stream: ByteStream {
@@ -32,6 +33,7 @@ func decodeLEB128<IntType, Stream>(
     return result
 }
 
+@inlinable
 func decodeLEB128<IntType, Stream>(
     stream: Stream
 ) throws -> IntType where IntType: FixedWidthInteger, IntType: RawSignedInteger, Stream: ByteStream {

Sources/WasmParser/ParsingLimits.swift

@@ -1,6 +1,8 @@
 /// Limits for parsing WebAssembly modules.
+@usableFromInline
 struct ParsingLimits {
     /// Maximum number of locals in a function.
+    @usableFromInline
     var maxFunctionLocals: UInt64
 
     /// The default limits for parsing.

Sources/WasmParser/Stream/Stream.swift

@@ -1,3 +1,4 @@
+@usableFromInline
 enum StreamError<Element>: Swift.Error, Equatable where Element: Hashable {
     case unexpectedEnd(expected: Set<Element>?)
     case unexpected(Element, index: Int, expected: Set<Element>?)