Eliminate the match_fail primop in v3_kernel and later passes

In the v3_life pass, it is assumed that a 'match_fail' primop
only occur at the top-level and at the end of a function.
But this code:

do_split_cases(A) ->
    case A of
        x ->
	    Z = dummy1;
        _ ->
	    Z = dummy2,
	    a=b
    end,
    Z.

will be optimized by sys_core_fold to the following code:

'split_cases'/1 =
    fun (_cor0) ->
	let <_cor7,Z> =
	    case _cor0 of
	      <'x'> when 'true' ->
		   < 'dummy1','dummy1' >
	      <_cor6> when 'true' ->
                  %% Here follows a 'match_fail' primop inside
		  %% multiple return values:
		  < primop 'match_fail'({'badmatch','b'}),'dummy2' >
	    end
	in
	    Z

moving the 'match_fail' primop into a "values" construction.

In the future, we would like to get rid of the v3_life pass (it is
there for historical reasons), so in the mean-time we prefer to not
add more code to it by generalizing the handling of 'match_fail'.

Since the 'match_fail' primop can be simulated by erlang:error/{1,2},
the simplest solution is to translate 'match_fail' to a call to
erlang:error/{1,2} in v3_kernel and remove the handling of
'match_fail' in v3_life and v3_codegen.

It is tempting to get rid of 'match_fail' also in the Core Erlang
format, but there are two issues:

- Removing the support for 'match_fail' completely may break tools
  that generate Core Erlang code. We should not do that in a minor
  release.

- There is no easy way to generate a 'function_clause' exception
  that will remain correct if it will be inlined into another
  function. (Calling "erlang:error(function_clause, Args)" is
  fine only if it is not inlined into another function.) A good
  solution probably involves introducing new instructions, which
  is better done in a major release.

Noticed-by: Håkan Matsson
Minimized-test-case-by: Erik Søe Sørensen

0 files changed, 0 insertions, 0 deletions