Move address maps to a section of the compiled image (#3240)

This commit moves the `address_map` field of `FunctionInfo` into a
custom-encoded section of the executable. The goal of this commit is, as
previous commits, to push less data through `bincode`. The `address_map`
field is actually extremely large and has huge benefits of not being
decoded when we load a module. This data is only used for traps and such
as well, so it's not overly important that it's massaged in to precise
data the runtime can extremely speedily use.

The `FunctionInfo` type does retain a tiny bit of information about the
function itself (it's start source location), but other than that the
`FunctionAddressMap` structure is moved from `wasmtime-environ` to
`wasmtime-cranelift` since it's now no longer needed outside of that
context.

crates/cranelift/src/lib.rs

@@ -94,7 +94,7 @@ use cranelift_codegen::isa::{unwind::UnwindInfo, CallConv, TargetIsa};
 use cranelift_entity::PrimaryMap;
 use cranelift_wasm::{DefinedFuncIndex, FuncIndex, WasmFuncType, WasmType};
 use target_lexicon::CallingConvention;
-use wasmtime_environ::{FunctionInfo, Module, TypeTables};
+use wasmtime_environ::{FilePos, FunctionInfo, InstructionAddressMap, Module, TypeTables};
 
 pub use builder::builder;
 
@@ -118,6 +118,10 @@ pub struct CompiledFunction {
     /// The unwind information.
     unwind_info: Option<UnwindInfo>,
 
+    /// Information used to translate from binary offsets back to the original
+    /// location found in the wasm input.
+    address_map: FunctionAddressMap,
+
     relocations: Vec<Relocation>,
     value_labels_ranges: cranelift_codegen::ValueLabelsRanges,
     stack_slots: ir::StackSlots,
@@ -125,6 +129,32 @@ pub struct CompiledFunction {
     info: FunctionInfo,
 }
 
+/// Function and its instructions addresses mappings.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+struct FunctionAddressMap {
+    /// An array of data for the instructions in this function, indicating where
+    /// each instruction maps back to in the original function.
+    ///
+    /// This array is sorted least-to-greatest by the `code_offset` field.
+    /// Additionally the span of each `InstructionAddressMap` is implicitly the
+    /// gap between it and the next item in the array.
+    instructions: Box<[InstructionAddressMap]>,
+
+    /// Function's initial offset in the source file, specified in bytes from
+    /// the front of the file.
+    start_srcloc: FilePos,
+
+    /// Function's end offset in the source file, specified in bytes from
+    /// the front of the file.
+    end_srcloc: FilePos,
+
+    /// Generated function body offset if applicable, otherwise 0.
+    body_offset: usize,
+
+    /// Generated function body length.
+    body_len: u32,
+}
+
 /// A record of a relocation to perform.
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct Relocation {