Move trap information to a section of the compiled image (#3241)

This commit moves the `traps` field of `FunctionInfo` into a section of
the compiled artifact produced by Cranelift. This section is quite large
and when previously encoded/decoded with `bincode` this can take quite
some time to process. Traps are expected to be relatively rare and it's
not necessarily the right tradeoff to spend so much time
serializing/deserializing this data, so this commit offloads the section
into a custom-encoded binary format located elsewhere in the compiled image.

This is similar to #3240 in its goal which is to move very large pieces
of metadata to their own sections to avoid decoding anything when we
load a precompiled modules. This also has a small benefit that it's
slightly more efficient storage for the trap information too, but that's
a negligible benefit.

This is part of #3230 to make loading modules fast.

crates/cranelift/src/compiler.rs

@@ -28,7 +28,7 @@ use std::sync::Mutex;
 use wasmtime_environ::{
     AddressMapSection, CompileError, FilePos, FlagValue, FunctionBodyData, FunctionInfo,
     InstructionAddressMap, Module, ModuleTranslation, StackMapInformation, TrapCode,
-    TrapInformation, Tunables, TypeTables, VMOffsets,
+    TrapEncodingBuilder, TrapInformation, Tunables, TypeTables, VMOffsets,
 };
 
 /// A compiler that compiles a WebAssembly module with Compiler, translating
@@ -208,8 +208,8 @@ impl wasmtime_environ::Compiler for Compiler {
             value_labels_ranges: ranges.unwrap_or(Default::default()),
             stack_slots: context.func.stack_slots,
             unwind_info,
+            traps: trap_sink.traps,
             info: FunctionInfo {
-                traps: trap_sink.traps,
                 start_srcloc: address_transform.start_srcloc,
                 stack_maps: stack_map_sink.finish(),
             },
@@ -249,10 +249,12 @@ impl wasmtime_environ::Compiler for Compiler {
 
         let mut builder = ObjectBuilder::new(obj, &translation.module);
         let mut addrs = AddressMapSection::default();
+        let mut traps = TrapEncodingBuilder::default();
 
         for (i, func) in funcs.iter() {
             let range = builder.func(i, func);
-            addrs.push(range, &func.address_map.instructions);
+            addrs.push(range.clone(), &func.address_map.instructions);
+            traps.push(range, &func.traps);
         }
         for (i, func) in trampolines.iter() {
             builder.trampoline(*i, func);
@@ -291,6 +293,7 @@ impl wasmtime_environ::Compiler for Compiler {
 
         builder.finish(&*self.isa)?;
         addrs.append_to(obj);
+        traps.append_to(obj);
 
         Ok(funcs.into_iter().map(|(_, f)| f.info).collect())
     }
@@ -533,6 +536,7 @@ impl Compiler {
             value_labels_ranges: Default::default(),
             info: Default::default(),
             address_map: Default::default(),
+            traps: Vec::new(),
         })
     }
 }