mero@hix ~/tmp/bug$ cat bug1.go 
package main

import "fmt"

func main() {
	type T1 int
	type T2 = T1
	a := struct{ T1 }{}
	b := struct{ T2 }{}
	fmt.Println(a == b)
}
mero@hix ~/tmp/bug$ go run bug1.go
# command-line-arguments
./bug1.go:10:16: invalid operation: a == b (mismatched types struct { T1 } and struct { T1 })
mero@hix ~/tmp/bug$ go run -compiler=gccgo bug1.go
# command-line-arguments
./bug1.go:10:16: error: incompatible types in binary expression
  fmt.Println(a == b)
                ^
mero@hix ~/tmp/bug$ cat bug2.go
package main

import "fmt"

func main() {
	type T1 int
	type T2 = T1
	a := interface{}(struct{ T1 }{})
	b := interface{}(struct{ T2 }{})
	fmt.Println(a == b)
}
mero@hix ~/tmp/bug$ go run bug2.go 
true
mero@hix ~/tmp/bug$ go run -compiler=gccgo bug2.go
false

go version devel +7da1f7addf Thu Nov 8 08:19:48 2018 +0000 linux/amd64
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mero/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mero"
GOPROXY=""
GORACE=""
GOROOT="/home/mero/go"
GOTMPDIR=""
GOTOOLDIR="/home/mero/go/pkg/tool/linux_amd64"
GCCGO="/usr/bin/gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
GOROOT/bin/go version: go version devel +7da1f7addf Thu Nov 8 08:19:48 2018 +0000 linux/amd64
GOROOT/bin/go tool compile -V: compile version devel +7da1f7addf Thu Nov 8 08:19:48 2018 +0000
uname -sr: Linux 4.18.16-200.fc28.x86_64
LSB Version:	:core-4.1-amd64:core-4.1-noarch
Distributor ID:	Fedora
Description:	Fedora release 28 (Twenty Eight)
Release:	28
Codename:	TwentyEight
/lib64/libc.so.6: GNU C Library (GNU libc) stable release version 2.27.
gdb --version: GNU gdb (GDB) Fedora 8.1.1-3.fc28