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authorBjörn Gustavsson <[email protected]>2015-09-25 07:06:38 +0200
committerBjörn Gustavsson <[email protected]>2015-09-28 10:26:40 +0200
commit464ca2f8049feec6453d2d9a327f996662978e51 (patch)
tree3b3cfa9a9edbd98ffd821512ea8c4173780c29bf /lib/compiler/src/beam_peep.erl
parentb66193afc3fe85072da4631c52c5ccec136caa05 (diff)
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Move select_val optimization from beam_clean to beam_peep
There is an optimization in beam_clean that will remove values having the same label as the failure label in a select_val instruction. Conceptually, this optimization is in the wrong module since ideally beam_clean is a mandatory pass that should not do optimizations. Furthermore, this part of beam_clean is called three times (from beam_dead, beam_peep, and as a compiler pass from the 'compile' module), but it only does useful one of the times it is called. Therefore, move this optimization to the beam_peep pass. The same optimization is done in beam_dead, but unfortunately it misses some opportunities for optimization because the code sharing optimization in beam_jump (share/1) runs after beam_dead. It would be more satisfactory to have this optimization only in beam_dead, but it turned out not to be trivial. If we try to run beam_jump:share/1 before beam_dead, some optimizations will no longer work in beam_dead because fallthroughs have been eliminated. For the moment, the possible solutions to this problem seems to involve more work and more complicated code than the gain from eliminating the duplicated optimization would gain.
Diffstat (limited to 'lib/compiler/src/beam_peep.erl')
-rw-r--r--lib/compiler/src/beam_peep.erl16
1 files changed, 16 insertions, 0 deletions
diff --git a/lib/compiler/src/beam_peep.erl b/lib/compiler/src/beam_peep.erl
index 75be86b83f..0c1abfe6a0 100644
--- a/lib/compiler/src/beam_peep.erl
+++ b/lib/compiler/src/beam_peep.erl
@@ -83,6 +83,16 @@ peep([{gc_bif,_,_,_,_,Dst}=I|Is], SeenTests0, Acc) ->
%% Kill all remembered tests that depend on the destination register.
SeenTests = kill_seen(Dst, SeenTests0),
peep(Is, SeenTests, [I|Acc]);
+peep([{select,Op,R,F,Vls0}|Is], _, Acc) ->
+ case prune_redundant_values(Vls0, F) of
+ [] ->
+ %% No values left. Must convert to plain jump.
+ I = {jump,F},
+ peep(Is, gb_sets:empty(), [I|Acc]);
+ [_|_]=Vls ->
+ I = {select,Op,R,F,Vls},
+ peep(Is, gb_sets:empty(), [I|Acc])
+ end;
peep([{test,Op,_,Ops}=I|Is], SeenTests0, Acc) ->
case beam_utils:is_pure_test(I) of
false ->
@@ -127,3 +137,9 @@ kill_seen_1([{_,Ops}=Test|T], Dst) ->
false -> [Test|kill_seen_1(T, Dst)]
end;
kill_seen_1([], _) -> [].
+
+prune_redundant_values([_Val,F|Vls], F) ->
+ prune_redundant_values(Vls, F);
+prune_redundant_values([Val,Lbl|Vls], F) ->
+ [Val,Lbl|prune_redundant_values(Vls, F)];
+prune_redundant_values([], _) -> [].