winch: Introduce winch-environ (#6017)

This commit introduces the `winch-environ` crate. This crate's responsibility is
to provide a shared implementatation of the `winch_codegen::FuncEnv` trait,
which is Winch's function compilation environment, used to resolve module and
runtime specific information needed by the code generation, such as resolving
all the details about a callee in a WebAssembly module, or resolving specific
information from the `VMContext`.

As of this change, the implementation only includes the necessary pieces to
resolve a function callee in a WebAssembly module. The idea is to evolve the
`winch_codegen::FuncEnv` trait as we evolve Winch's code generation.

winch/environ/src/lib.rs

@@ -0,0 +1,41 @@
+//! This crate implements Winch's function compilation environment,
+//! which allows Winch's code generation to resolve module and runtime
+//! specific information.  This crate mainly implements the
+//! `winch_codegen::FuncEnv` trait.
+
+use wasmparser::types::Types;
+use wasmtime_environ::{FuncIndex, Module};
+use winch_codegen::{self, Callee, TargetIsa};
+
+/// Function environment containing module and runtime specific
+/// information.
+pub struct FuncEnv<'a> {
+    /// The translated WebAssembly module.
+    pub module: &'a Module,
+    /// Type information about a module, once it has been validated.
+    pub types: &'a Types,
+    /// The current ISA.
+    pub isa: &'a dyn TargetIsa,
+}
+
+impl<'a> winch_codegen::FuncEnv for FuncEnv<'a> {
+    fn callee_from_index(&self, index: u32) -> Callee {
+        let func = self
+            .types
+            .function_at(index)
+            .unwrap_or_else(|| panic!("function type at index: {}", index));
+
+        Callee {
+            ty: func.clone(),
+            import: self.module.is_imported_function(FuncIndex::from_u32(index)),
+            index,
+        }
+    }
+}
+
+impl<'a> FuncEnv<'a> {
+    /// Create a new function environment.
+    pub fn new(module: &'a Module, types: &'a Types, isa: &'a dyn TargetIsa) -> Self {
+        Self { module, types, isa }
+    }
+}