cmd/compile: add flag to FOR/RANGE to preserve loop semantics across inlines

This modifies the loopvar change to be tied to the
package if it is specified that way, and preserves
the change across inlining.

Down the road, this will be triggered (and flow correctly)
if the changed semantics are tied to Go version specified
in go.mod (or rather, for the compiler, by the specified
version for compilation).

Includes tests.

Change-Id: If54e8b6dd23273b86be5ba47838c90d38af9bd1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/463595
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 64173312ac..6098c92ac9 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -1857,7 +1857,7 @@ func (r *reader) forStmt(label *types.Sym) ir.Node {
 
 	if r.Bool() {
 		pos := r.pos()
-		rang := ir.NewRangeStmt(pos, nil, nil, nil, nil)
+		rang := ir.NewRangeStmt(pos, nil, nil, nil, nil, false)
 		rang.Label = label
 
 		names, lhs := r.assignList()
@@ -1881,6 +1881,7 @@ func (r *reader) forStmt(label *types.Sym) ir.Node {
 		}
 
 		rang.Body = r.blockStmt()
+		rang.DistinctVars = r.Bool()
 		r.closeAnotherScope()
 
 		return rang
@@ -1891,9 +1892,10 @@ func (r *reader) forStmt(label *types.Sym) ir.Node {
 	cond := r.optExpr()
 	post := r.stmt()
 	body := r.blockStmt()
+	dv := r.Bool()
 	r.closeAnotherScope()
 
-	stmt := ir.NewForStmt(pos, init, cond, post, body)
+	stmt := ir.NewForStmt(pos, init, cond, post, body, dv)
 	stmt.Label = label
 	return stmt
 }