Implement canon lower of a canon lift function in the same component (#4347)

* Implement `canon lower` of a `canon lift` function in the same component

This commit implements the "degenerate" logic for implementing a
function within a component that is lifted and then immediately lowered
again. In this situation the lowered function will immediately generate
a trap and doesn't need to implement anything else.

The implementation in this commit is somewhat heavyweight but I think is
probably justified moreso in future additions to the component model
rather than what exactly is here right now. It's not expected that this
"always trap" functionality will really be used all that often since it
would generally mean a buggy component, but the functionality plumbed
through here is hopefully going to be useful for implementing
component-to-component adapter trampolines.

Specifically this commit implements a strategy where the `canon.lower`'d
function is generated by Cranelift and simply has a single trap
instruction when called, doing nothing else. The main complexity comes
from juggling around all the data associated with these functions,
primarily plumbing through the traps into the `ModuleRegistry` to
ensure that the global `is_wasm_trap_pc` function returns `true` and at
runtime when we lookup information about the trap it's all readily
available (e.g. translating the trapping pc to a `TrapCode`).

* Fix non-component build

* Fix some offset calculations

* Only create one "always trap" per signature

Use an internal map to deduplicate during compilation.

crates/cranelift/src/compiler.rs

@@ -342,6 +342,7 @@ impl wasmtime_environ::Compiler for Compiler {
             .iter()
             .zip(&compiled_trampolines)
         {
+            assert!(func.traps.is_empty());
             trampolines.push(builder.trampoline(*i, &func));
         }
 
@@ -683,19 +684,21 @@ impl Compiler {
         context
             .compile_and_emit(isa, &mut code_buf)
             .map_err(|error| CompileError::Codegen(pretty_error(&context.func, error)))?;
+        let result = context.mach_compile_result.as_ref().unwrap();
 
         // Processing relocations isn't the hardest thing in the world here but
         // no trampoline should currently generate a relocation, so assert that
         // they're all empty and if this ever trips in the future then handling
         // will need to be added here to ensure they make their way into the
         // `CompiledFunction` below.
-        assert!(context
-            .mach_compile_result
-            .as_ref()
-            .unwrap()
+        assert!(result.buffer.relocs().is_empty());
+
+        let traps = result
             .buffer
-            .relocs()
-            .is_empty());
+            .traps()
+            .into_iter()
+            .map(mach_trap_to_trap)
+            .collect::<Vec<_>>();
 
         let unwind_info = if isa.flags().unwind_info() {
             context
@@ -713,7 +716,7 @@ impl Compiler {
             value_labels_ranges: Default::default(),
             info: Default::default(),
             address_map: Default::default(),
-            traps: Vec::new(),
+            traps,
         })
     }
 
@@ -889,6 +892,8 @@ fn mach_reloc_to_reloc(reloc: &MachReloc) -> Relocation {
     }
 }
 
+const ALWAYS_TRAP_CODE: u16 = 100;
+
 fn mach_trap_to_trap(trap: &MachTrap) -> TrapInformation {
     let &MachTrap { offset, code } = trap;
     TrapInformation {
@@ -905,6 +910,7 @@ fn mach_trap_to_trap(trap: &MachTrap) -> TrapInformation {
             ir::TrapCode::BadConversionToInteger => TrapCode::BadConversionToInteger,
             ir::TrapCode::UnreachableCodeReached => TrapCode::UnreachableCodeReached,
             ir::TrapCode::Interrupt => TrapCode::Interrupt,
+            ir::TrapCode::User(ALWAYS_TRAP_CODE) => TrapCode::AlwaysTrapAdapter,
 
             // these should never be emitted by wasmtime-cranelift
             ir::TrapCode::User(_) => unreachable!(),