test: add test coverage for type-switch hash collisions

This CL expands the test for #29612 to check that type switches also
work correctly when type hashes collide.

Change-Id: Ia153743e6ea0736c1a33191acfe4d8ba890be527
Reviewed-on: https://go-review.googlesource.com/c/go/+/195782
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue29612.dir/main.go

@@ -10,6 +10,8 @@
 package main
 
 import (
+	"fmt"
+
 	ssa1 "./p1/ssa"
 	ssa2 "./p2/ssa"
 )
@@ -21,4 +23,27 @@ func main() {
 	v2 := &ssa2.T{}
 	ssa2.Works(v2)
 	ssa2.Panics(v2) // This call must not panic
+
+	swt(v1, 1)
+	swt(v2, 2)
+}
+
+//go:noinline
+func swt(i interface{}, want int) {
+	var got int
+	switch i.(type) {
+	case *ssa1.T:
+		got = 1
+	case *ssa2.T:
+		got = 2
+
+	case int8, int16, int32, int64:
+		got = 3
+	case uint8, uint16, uint32, uint64:
+		got = 4
+	}
+
+	if got != want {
+		panic(fmt.Sprintf("switch %v: got %d, want %d", i, got, want))
+	}
 }