cmd/compile: fix panic in field tracking logic

Within the frontend, we generally don't guarantee uniqueness of
anonymous types. For example, each struct type literal gets
represented by its own types.Type instance.

However, the field tracking code was using the struct type as a map
key. This broke in, because that CL started
changing the inlined parameter variables from using the types.Type of
the declared parameter to that of the call site argument. These are
always identical types (e.g., types.Identical would report true), but
they can be different pointer values, causing the map lookup to fail.

The easiest fix is to simply get rid of the map and instead use
Node.Opt for tracking the types.Field. To mitigate against more latent
field tracking failures (e.g., if any other code were to start trying
to use Opt on ODOT/ODOTPTR fields), we store this field
unconditionally. I also expect having the types.Field will be useful
to other frontend code in the future.

Finally, to make it easier to test field tracking without having to
run make.bash with GOEXPERIMENT=fieldtrack, this commit adds a
-d=fieldtrack flag as an alternative way to enable field tracking
within the compiler. See also #42681.

Fixes #42686.

Change-Id: I6923d206d5e2cab1e6798cba36cae96c1eeaea55
Run-TryBot: Matthew Dempsky <>
TryBot-Result: Go Bot <>
Reviewed-by: Cherry Zhang <>
Trust: Matthew Dempsky <>
4 files changed
tree: b9f558769fb79aa83efe9c0283fdd71ddb69ab66
  1. .gitattributes
  2. .github/
  3. .gitignore
  11. api/
  12. doc/
  13. favicon.ico
  14. lib/
  15. misc/
  16. robots.txt
  17. src/
  18. test/

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

Gopher image Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.

Our canonical Git repository is located at There is a mirror of the repository at

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

Download and Install

Binary Distributions

Official binary distributions are available at

After downloading a binary release, visit or load doc/install.html in your web browser for installation instructions.

Install From Source

If a binary distribution is not available for your combination of operating system and architecture, visit or load doc/install-source.html in your web browser for source installation instructions.


Go is the work of thousands of contributors. We appreciate your help!

To contribute, please read the contribution guidelines:

Note that the Go project uses the issue tracker for bug reports and proposals only. See for a list of places to ask questions about the Go language.