diff options
Diffstat (limited to 'lib/compiler')
| -rw-r--r-- | lib/compiler/internal_doc/cerl-notes.md | 75 | ||||
| -rw-r--r-- | lib/compiler/src/cerl_clauses.erl | 2 | ||||
| -rw-r--r-- | lib/compiler/src/compile.erl | 8 | ||||
| -rw-r--r-- | lib/compiler/test/compile_SUITE.erl | 19 | ||||
| -rw-r--r-- | lib/compiler/test/compile_SUITE_data/deterministic_module.erl | 21 |
5 files changed, 118 insertions, 7 deletions
diff --git a/lib/compiler/internal_doc/cerl-notes.md b/lib/compiler/internal_doc/cerl-notes.md new file mode 100644 index 0000000000..705fe8f42d --- /dev/null +++ b/lib/compiler/internal_doc/cerl-notes.md @@ -0,0 +1,75 @@ +Some notes on the cerl modules +============================== + +Maps in cerl_clauses:match/3 +---------------------------- + +Not much optimization is done for maps in `cerl_clauses:match/3`. + +The reason is that the inliner (`cerl_inline`) was not designed for +data types that depend on variables bound in the enclosing environment +(for example, the keys for maps). If we attempt to extend the +optimizations for maps similar to the optimizations for the other data +types, the inliner will crash for certain code. Here is an example of +code that would crash the inliner: + + t() -> + f(key). + + f(K) -> + case #{K => value} of + #{key := V} -> V + end. + +The reason for the crash is that the inliner works in several +passes and calls `cerl_clauses:match/3` twice. The inliner will +assume that the same result will be returned both times, but +for this example different bindings will be returned. + +Here is the rough outline of what happens: + +* The first time `cerl_clauses:match/3` will be asked to match the +pattern `#{K := V}` against `#{key => value}`. It cannot say more +than that the pattern *may* match. + +* Now the inliner will add the bindings to body of the clause (which +is simply `V`). In this case, the bindings are still empty, so +nothing is added. + +* The inliner will now do some substitutions and renaming. The +variable `K` will be replaced with `key`. + +* The next time `cerl_clauses:match/3` is called, it will be asked to +match the pattern `#{key := V}` against `#{key => value#}`. In this +case, there will be a match and the bindings can be extended with +`{V,value}`. + +* The inliner will see that the entire case can be removed. Only +the body for the clause needs to be kept. + +Thus, after inlining the function `t/0` will look like this: + + t() -> + V. + +The problem here is that the inliner assumed that the bindings from +the first and second call to `cer_clauses:match/3` would be the same. +It used the empty bindings from the first call for the body. + +The correct way would be to add the bindings from the second call: + + t() -> + let V = value in V. + +### How to fix this ### + +The inliner will need to call `cerl_clauses:match/3` after doing +all substitutions and renaming. It is not clear to me how difficult +that would be. I assume that the inliner is written the way it is +for a good reason. That means that switching the order things are +done would lead to correctness and/or performance problems. + +### What must also be done to fix this ### + +`cerl_inline:make_template/3` must be extended to create a template +for maps. That is relatively straightforward. diff --git a/lib/compiler/src/cerl_clauses.erl b/lib/compiler/src/cerl_clauses.erl index 7d6518c3c6..fa5104c01b 100644 --- a/lib/compiler/src/cerl_clauses.erl +++ b/lib/compiler/src/cerl_clauses.erl @@ -353,6 +353,8 @@ match(P, E, Bs) -> map -> %% The most we can do is to say "definitely no match" if a %% map pattern is matched against non-map data. + %% (Note: See the document internal_doc/cerl-notes.md for + %% information why we don't try to do more here.) case E of any -> {false, Bs}; diff --git a/lib/compiler/src/compile.erl b/lib/compiler/src/compile.erl index bc519264fc..b0d0da0f66 100644 --- a/lib/compiler/src/compile.erl +++ b/lib/compiler/src/compile.erl @@ -1448,16 +1448,16 @@ beam_asm(Code0, #compile{ifile=File,extra_chunks=ExtraChunks,options=CompilerOpt {ok,DebugInfo,Opts0} -> Opts1 = [O || O <- Opts0, effects_code_generation(O)], Chunks = [{<<"Dbgi">>, DebugInfo} | ExtraChunks], - CompileInfo = compile_info(File, Opts1), + CompileInfo = compile_info(File, CompilerOpts, Opts1), {ok,Code} = beam_asm:module(Code0, Chunks, CompileInfo, CompilerOpts), {ok,Code,St#compile{abstract_code=[]}}; {error,Es} -> {error,St#compile{errors=St#compile.errors ++ [{File,Es}]}} end. -compile_info(File, Opts) -> - IsSlim = member(slim, Opts), - IsDeterministic = member(deterministic, Opts), +compile_info(File, CompilerOpts, Opts) -> + IsSlim = member(slim, CompilerOpts), + IsDeterministic = member(deterministic, CompilerOpts), Info0 = proplists:get_value(compile_info, Opts, []), Info1 = case paranoid_absname(File) of diff --git a/lib/compiler/test/compile_SUITE.erl b/lib/compiler/test/compile_SUITE.erl index e88a132d59..8fe2a93f95 100644 --- a/lib/compiler/test/compile_SUITE.erl +++ b/lib/compiler/test/compile_SUITE.erl @@ -120,9 +120,19 @@ file_1(Config) when is_list(Config) -> true = exists(Target), passed = run(Target, test, []), + %% Test option 'deterministic' as a compiler attribute. + Det = deterministic_module, + {DetPath, DetTarget} = get_files(Config, Det, "det_target"), + {ok,Det,DetCode} = compile:file(DetPath, [binary]), + {module,Det} = code:load_binary(Det, "", DetCode), + [{version,_}] = Det:module_info(compile), + true = code:delete(Det), + false = code:purge(Det), + %% Cleanup. ok = file:delete(Target), ok = file:del_dir(filename:dirname(Target)), + ok = file:del_dir(filename:dirname(DetTarget)), %% There should not be any messages in the messages. receive @@ -1318,10 +1328,13 @@ do_warnings_2([], Next, F) -> %% pre-loads the modules that are used by a typical compilation. pre_load_check(Config) -> - case test_server:is_cover() of - true -> + case {test_server:is_cover(),code:module_info(native)} of + {true,_} -> {skip,"Cover is running"}; - false -> + {false,true} -> + %% Tracing won't work. + {skip,"'code' is native-compiled"}; + {false,false} -> try do_pre_load_check(Config) after diff --git a/lib/compiler/test/compile_SUITE_data/deterministic_module.erl b/lib/compiler/test/compile_SUITE_data/deterministic_module.erl new file mode 100644 index 0000000000..5e0e29c25e --- /dev/null +++ b/lib/compiler/test/compile_SUITE_data/deterministic_module.erl @@ -0,0 +1,21 @@ +%% +%% %CopyrightBegin% +%% +%% Copyright Ericsson AB 2017. All Rights Reserved. +%% +%% Licensed under the Apache License, Version 2.0 (the "License"); +%% you may not use this file except in compliance with the License. +%% You may obtain a copy of the License at +%% +%% http://www.apache.org/licenses/LICENSE-2.0 +%% +%% Unless required by applicable law or agreed to in writing, software +%% distributed under the License is distributed on an "AS IS" BASIS, +%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +%% See the License for the specific language governing permissions and +%% limitations under the License. +%% +%% %CopyrightEnd% +%% +-module(deterministic_module). +-compile([deterministic]). |