cmd/compile: add CONVIFACE nodes needed in generic code due to assignments

Added new function earlyTransformAssign() to add needed CONVIFACE nodes
due to assignments in generic functions.

Fixes #48049

Change-Id: I7cd9cee6ecf34ed2ef0743d1b17645b9f520fa00
Reviewed-on: https://go-review.googlesource.com/c/go/+/347914
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/transform.go b/src/cmd/compile/internal/noder/transform.go
index 180891b5b5..b278f3db09 100644
--- a/src/cmd/compile/internal/noder/transform.go
+++ b/src/cmd/compile/internal/noder/transform.go
@@ -365,6 +365,59 @@ assignOK:
 	}
 }
 
+// Version of transformAssign that can run on generic code that adds CONVIFACE calls
+// as needed (and rewrites multi-value calls).
+func earlyTransformAssign(stmt ir.Node, lhs, rhs []ir.Node) {
+	cr := len(rhs)
+	if len(rhs) == 1 {
+		if rtyp := rhs[0].Type(); rtyp != nil && rtyp.IsFuncArgStruct() {
+			cr = rtyp.NumFields()
+		}
+	}
+
+	// x,y,z = f()
+	_, isCallExpr := rhs[0].(*ir.CallExpr)
+	if isCallExpr && cr > len(rhs) {
+		stmt := stmt.(*ir.AssignListStmt)
+		stmt.SetOp(ir.OAS2FUNC)
+		r := rhs[0].(*ir.CallExpr)
+		rtyp := r.Type()
+
+		mismatched := false
+		failed := false
+		for i := range lhs {
+			result := rtyp.Field(i).Type
+
+			if lhs[i].Type() == nil || result == nil {
+				failed = true
+			} else if lhs[i] != ir.BlankNode && !types.Identical(lhs[i].Type(), result) {
+				mismatched = true
+			}
+		}
+		if mismatched && !failed {
+			typecheck.RewriteMultiValueCall(stmt, r)
+		}
+		return
+	}
+
+	// x, ok = y
+	if len(lhs) != len(rhs) {
+		assert(len(lhs) == 2 && len(rhs) == 1)
+		// TODO(danscales): deal with case where x or ok is an interface
+		// type. We want to add CONVIFACE now, but that is tricky, because
+		// the rhs may be AS2MAPR, AS2RECV, etc. which has two result values,
+		// and that is not rewritten until the order phase (o.stmt, as2ok).
+		return
+	}
+
+	// Check for interface conversion on each assignment
+	for i, r := range rhs {
+		if lhs[i].Type() != nil && lhs[i].Type().IsInterface() {
+			rhs[i] = assignconvfn(r, lhs[i].Type())
+		}
+	}
+}
+
 // Corresponds to typecheck.typecheckargs.  Really just deals with multi-value calls.
 func transformArgs(n ir.InitNode) {
 	var list []ir.Node