commit 6479d5976c5d848ec6f5843041275723a00006b0
author Ian Lance Taylor <iant@golang.org> Thu Jun 30 17:40:00 2022 -0700
committer Ian Lance Taylor <iant@golang.org> Fri Jul 01 22:43:23 2022 +0000
tree cd84aee70e7c5bf07a74dc8391526d3ab32c71cf
parent ac438edc5335f69c95df9342f43712ad2f61ad66

compiler: use correct init order for multi-value initialization

Use the correct initialization order for

var a = c
var b, c = x.(bool)

The global c is initialized by the preinit of b, but were missing a
dependency of c on b, so a would be initialized to the zero value of c
rather than the correct value.

Simply adding the dependency of c on b didn't work because the preinit
of b refers to c, so that appeared circular.  So this patch changes
the init order to skip dependencies that only appear on the left hand
side of assignments in preinit blocks.

Doing that didn't work because the write barrier pass can transform "a
= b" into code like "gcWriteBarrier(&a, b)" that is not obviously a
simple assigment.  So this patch moves the collection of dependencies
to just after lowering, before the write barriers are inserted.

Making those changes permit relaxing the requirement that we don't
warn about self-dependency in preinit blocks, so now we correctly warn
for

var a, b any = b.(bool)

The test case is https://go.dev/cl/415238.

Fixes golang/go#53619

Change-Id: I095b5a330ab657fc3c7b366e85c881c2a80e5a1a
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/415594
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>