As far as I can tell, alpha can be emulated by QEMU. VAX has SIMH. (Perhaps I should mention it somewhere? :))
Index: backends.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/backends.html,v retrieving revision 1.84 diff -u -r1.84 backends.html --- backends.html 18 Jan 2019 11:52:12 -0000 1.84 +++ backends.html 31 Mar 2019 08:00:23 -0000 @@ -69,7 +69,7 @@ Target | HMSLQNFICBD lqrcpbfmgiates -----------+--------------------------- aarch64 | Q q b gia s -alpha | ?? Q C q mgi e +alpha | ? Q C q mgi e arc | B b gia arm | b ia s avr | L FI l cp g @@ -116,7 +116,7 @@ tilegx | S Q C q gi e tilepro | S F C gi e v850 | g a s -vax | M? I c b i e +vax | M I c b i e visium | B g t s xtensa | C </pre>
