compiler: Warn if the size of a binary segment is invalid

The compiler would silently accept and Dialyzer would crash on
code like:

  <<X:(2.5)>>

It is never acceptable for Dialyzer to crash. The compiler should
at least generate a warning for such code. It is tempting to let
the compiler generate an error, but that would mean that code like:

  Sz = 42.0,
  <<X:Sz>>.

would be possible to compile with optimizations disabled, but not
with optimizations enabled.

Dialyzer crashes because it calls cerl:bitstr_bitsize/1, which
crashes if the type of size for the segment is invalid. The easiest
way to avoid that crash is to extend the sanity checks in v3_core
to also include the size field of binary segments. That will cause
the compiler to issue a warning and to replace the bad binary
construction with a call to erlang:error/1. (It also means that
Dialyzer will not issue a warning for bad size fields.)

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/compiler/test/bs_construct_SUITE.erl b/lib/compiler/test/bs_construct_SUITE.erl
index 31c7890f26..e8b30f44ce 100644
--- a/lib/compiler/test/bs_construct_SUITE.erl
+++ b/lib/compiler/test/bs_construct_SUITE.erl
@@ -468,6 +468,10 @@ opt(Config) when is_list(Config) ->
     ?line {'EXIT',_} = (catch <<<<23,56,0,2>>:64/float>>),
     ?line {'EXIT',_} = (catch <<<<23,56,0,2:7>>/binary>>),
 
+    %% Test constant propagation - there should be a warning.
+    BadSz = 2.5,
+    {'EXIT',_} = (catch <<<<N,56,0,2>>:BadSz/binary>>),
+
     case id(false) of
 	true -> ?line opt_dont_call_me();
 	false -> ok