tree e343d7913b87186fde835b78d1a0a98345ea204b
parent 951c83af46375019b2fe262635746368a6b9c4ba
author Cherry Zhang <cherryyz@google.com> 1559171754 -0400
committer Ian Lance Taylor <iant@golang.org> 1559604991 +0000

compiler, runtime, reflect: generate unique type descriptors

Currently, the compiler already generates common symbols for type
descriptors, so the type descriptors are unique. However, when a
type is created through reflection, it is not deduplicated with
compiler-generated types. As a consequence, we cannot assume type
descriptors are unique, and cannot use pointer equality to
compare them. Also, when constructing a reflect.Type, it has to
go through a canonicalization map, which introduces overhead to
reflect.TypeOf, and lock contentions in concurrent programs.

In order for the reflect package to deduplicate types with
compiler-created types, we register all the compiler-created type
descriptors at startup time. The reflect package, when it needs
to create a type, looks up the registry of compiler-created types
before creates a new one. There is no lock contention since the
registry is read-only after initialization.

This lets us get rid of the canonicalization map, and also makes
it possible to compare type descriptors with pointer equality.

Change-Id: Ia828bba0694e9b67398269959ed7b65b4b1b43b7
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/179598
Reviewed-by: Ian Lance Taylor <iant@golang.org>