Use same CompiledCode for import replacement (#478)

This commit allows CompiledCode to be re-used regardless of
the existence of import replacement configs for instantiation.

In order to achieve this, we introduce ModuleID, which is sha256
checksum calculated on source bytes, as a key for module compilation
cache. Previously, we used*wasm.Module as keys for caches which
differ before/after import replacement.

Signed-off-by: Takeshi Yoneda takeshi@tetrate.io

builder.go

@@ -256,9 +256,7 @@ func (b *moduleBuilder) Build() (*CompiledCode, error) {
 		return nil, err
 	}
 
-	ret := &CompiledCode{module: module}
-	ret.addCacheEntry(module, b.r.store.Engine)
-	return &CompiledCode{module: module}, nil
+	return &CompiledCode{module: module, compiledEngine: b.r.store.Engine}, nil
 }
 
 // Instantiate implements ModuleBuilder.Instantiate