cmd/compile: fix the index variable is shadowed in dictPass

The CL 349613 causes this problem.
In fact, we want to use the outer i to find m.List[i],
but the newly created index variable i in the nearest
for range shadow the outer i.

Fixes #48838.

Change-Id: I10f0bd985340f9443eefaadda6fc56e4e7e9a10c
Reviewed-on: https://go-review.googlesource.com/c/go/+/354549
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Dan Scales <danscales@google.com>

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 2bc1756b8d8d8e120264b0c99f2b9fbf96718579..62d6a45819b82a7e12cde2057a0947e0485536d4 100644 (file)
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -1298,9 +1298,9 @@ func (g *irgen) dictPass(info *instInfo) {
                                                        // Type switch from nonempty interface. We need a *runtime.itab
                                                        // for the dynamic type.
                                                        ix := -1
-                                                       for i, ic := range info.dictInfo.itabConvs {
+                                                       for j, ic := range info.dictInfo.itabConvs {
                                                                if ic == m.List[i] {
-                                                                       ix = info.dictInfo.startItabConv + i
+                                                                       ix = info.dictInfo.startItabConv + j
                                                                        break
                                                                }
                                                        }

diff --git a/test/typeparam/issue48838.go b/test/typeparam/issue48838.go
new file mode 100644 (file)
index 0000000..ef2150d
--- /dev/null
+++ b/test/typeparam/issue48838.go
@@ -0,0 +1,31 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func main() {
+       check[string]()
+}
+
+func check[T any]() {
+       var result setter[T]
+       switch result.(type) {
+       case fooA[T]:
+       case fooB[T]:
+       }
+}
+
+type setter[T any] interface {
+       Set(T)
+}
+
+type fooA[T any] struct{}
+
+func (fooA[T]) Set(T) {}
+
+type fooB[T any] struct{}
+
+func (fooB[T]) Set(T) {}