beam_validator: Strengthen validation of GC instructions

beam_validator did not verify that the Y registers were initialized
before executing the following instructions that could cause a GC:

    bs_append/8
    bs_init2/6
    bs_init_bits/6
    gc_bif1/5
    gc_bif2/6
    gc_bif3/7
    test_heap/2

That means that, for example, an incorrect optimization that replaced
an 'allocate_zero' instruction with an 'allocate' instruction when it
was not safe, would not be rejected by beam_validtor, but would
instead cause a crash or other undefined behavior at runtime.

Also fix a minor bug in beam_type exposed by the stronger checking.
When compiling from .S files, beam_type did not handle the
init/1 instruction and could produce unsafe code.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/compiler/src/beam_type.erl b/lib/compiler/src/beam_type.erl
index 3d842a6fd3..3446430aaf 100644
--- a/lib/compiler/src/beam_type.erl
+++ b/lib/compiler/src/beam_type.erl
@@ -367,6 +367,8 @@ flt_need_heap_2({set,_,_,get_list}, H, Fl) ->
     {[],H,Fl};
 flt_need_heap_2({set,_,_,{try_catch,_,_}}, H, Fl) ->
     {[],H,Fl};
+flt_need_heap_2({set,_,_,init}, H, Fl) ->
+    {[],H,Fl};
 %% All other instructions should cause the insertion of an allocation
 %% instruction if needed.
 flt_need_heap_2(_, H, Fl) ->