Allow instance allocators control over module compilation.

This commit introduces two new methods on `InstanceAllocator`:

* `validate_module` - this method is used to validate a module after
  translation but before compilation. It will be used for the upcoming pooling
  allocator to ensure a module being compiled adheres to the limits of the
  allocator.

* `adjust_tunables` - this method is used to adjust the `Tunables` given the
  JIT compiler.  The pooling allocator will use this to force all memories to
  be static during compilation.

crates/environ/src/module.rs

@@ -42,8 +42,16 @@ impl MemoryStyle {
         // A heap with a maximum that doesn't exceed the static memory bound specified by the
         // tunables make it static.
         //
-        // If the module doesn't declare an explicit maximum treat it as 4GiB.
-        let maximum = memory.maximum.unwrap_or(WASM_MAX_PAGES);
+        // If the module doesn't declare an explicit maximum treat it as 4GiB when not
+        // requested to use the static memory bound itself as the maximum.
+        let maximum = memory
+            .maximum
+            .unwrap_or(if tunables.static_memory_bound_is_maximum {
+                tunables.static_memory_bound
+            } else {
+                WASM_MAX_PAGES
+            });
+
         if maximum <= tunables.static_memory_bound {
             assert_ge!(tunables.static_memory_bound, memory.minimum);
             return (

crates/environ/src/tunables.rs

@@ -27,6 +27,9 @@ pub struct Tunables {
     /// Whether or not fuel is enabled for generated code, meaning that fuel
     /// will be consumed every time a wasm instruction is executed.
     pub consume_fuel: bool,
+
+    /// Whether or not to treat the static memory bound as the maximum for unbounded heaps.
+    pub static_memory_bound_is_maximum: bool,
 }
 
 impl Default for Tunables {
@@ -62,6 +65,7 @@ impl Default for Tunables {
             parse_wasm_debuginfo: true,
             interruptable: false,
             consume_fuel: false,
+            static_memory_bound_is_maximum: false,
         }
     }
 }