[dev.regabi] cmd/compile: fix package-initialization order

This CL fixes package initialization order by creating the init task
before the general deadcode-removal pass.

It also changes noder to emit zero-initialization assignments (i.e.,
OAS with nil RHS) for package-block variables, so that initOrder can
tell the variables still need initialization. To allow this, we need
to also extend the static-init code to recognize zero-initialization
assignments.

This doesn't pass toolstash -cmp, because it reorders some package
initialization routines.

Fixes #43444.

Change-Id: I0da7996a62c85e15e97ce965298127e075390a7e
Reviewed-on: https://go-review.googlesource.com/c/go/+/280976
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/src/cmd/compile/internal/staticinit/sched.go b/src/cmd/compile/internal/staticinit/sched.go
index 1b0af1b05d..8e4ce55954 100644
--- a/src/cmd/compile/internal/staticinit/sched.go
+++ b/src/cmd/compile/internal/staticinit/sched.go
@@ -86,17 +86,22 @@ func (s *Schedule) staticcopy(l *ir.Name, loff int64, rn *ir.Name, typ *types.Ty
 	if rn.Class_ != ir.PEXTERN || rn.Sym().Pkg != types.LocalPkg {
 		return false
 	}
-	if rn.Defn == nil { // probably zeroed but perhaps supplied externally and of unknown value
-		return false
-	}
 	if rn.Defn.Op() != ir.OAS {
 		return false
 	}
 	if rn.Type().IsString() { // perhaps overwritten by cmd/link -X (#34675)
 		return false
 	}
+	if rn.Embed != nil {
+		return false
+	}
 	orig := rn
 	r := rn.Defn.(*ir.AssignStmt).Y
+	if r == nil {
+		// No explicit initialization value. Probably zeroed but perhaps
+		// supplied externally and of unknown value.
+		return false
+	}
 
 	for r.Op() == ir.OCONVNOP && !types.Identical(r.Type(), typ) {
 		r = r.(*ir.ConvExpr).X
@@ -185,6 +190,11 @@ func (s *Schedule) staticcopy(l *ir.Name, loff int64, rn *ir.Name, typ *types.Ty
 }
 
 func (s *Schedule) StaticAssign(l *ir.Name, loff int64, r ir.Node, typ *types.Type) bool {
+	if r == nil {
+		// No explicit initialization value. Either zero or supplied
+		// externally.
+		return true
+	}
 	for r.Op() == ir.OCONVNOP {
 		r = r.(*ir.ConvExpr).X
 	}