Improve binary matching of literals

The bs_match_string instruction is used to speed up matching of
binary literals. For example, given this source code:

foo1(<<1,2,3>>) -> ok.

The matching part of the code will look like:

    {test,bs_start_match2,{f,1},1,[{x,0},0],{x,0}}.
    {test,bs_match_string,{f,3},[{x,0},24,{string,[1,2,3]}]}.
    {test,bs_test_tail2,{f,3},[{x,0},0]}.

Nice. However, if we do a simple change to the source code:

foo2(<<1,2,3>>) -> ok;
foo2(<<>>) -> error.

the resulting matching code will look like (sligthly simplified):

    {test,bs_start_match2,{f,4},1,[{x,0},0],{x,0}}.
    {test,bs_get_integer2,{f,7},1,[{x,0},{integer,8},1,Flags],{x,1}}.
    {test,is_eq_exact,{f,8},[{x,1},{integer,1}]}.
    {test,bs_match_string,{f,6},[{x,0},16,{string,[2,3]}]}.
    {test,bs_test_tail2,{f,6},[{x,0},0]}.
    {move,{atom,ok},{x,0}}.
    return.
  {label,6}.
    {bs_restore2,{x,0},{atom,start}}.
  {label,7}.
    {test,bs_test_tail2,{f,8},[{x,0},0]}.

That is, matching of the first byte is not combined into the
bs_match_string instruction that follows.

Fix this problem by allowing a bs_match_string instruction to be
used if all clauses will match either the same integer literal or
the empty binary.

0 files changed, 0 insertions, 0 deletions