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authorAnthony Ramine <[email protected]>2014-02-07 02:07:04 +0100
committerAnthony Ramine <[email protected]>2014-02-11 01:59:33 +0100
commit85cc321c5d3d1e78a895a549a856266228a75a02 (patch)
tree231a8cc1924b8f86b0b493088199231a749c6a2d
parentf8723a8fe3cba291df7e087619bf4f8ee502ce52 (diff)
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Optimise case arguments in sys_core_fold
If the argument of a case expression is a let, a seq or a case with two clauses where the second one is a failing clause; it can be moved outside the case and further optimisations can be performed. module 'foo' ['t'/4] attributes [] 't'/4 = fun (_cor14,Sub0,_cor15,_cor16) -> let Ssa = call 'erlang':'get' ('foo') in case let Ssa = {'ssa',_cor14,Sub0,_cor15,_cor16} in let _rec11 = call 'erlang':'+' (_cor14, 1) in let _cor4 = call 'erlang':'setelement' (2, Ssa, _rec11) in {{'tmp',_cor14},_cor4} of {NewReg,Foo} when 'true' -> {NewReg,Foo,Ssa} _cor20 when 'true' -> primop 'match_failure' ({'case_clause',_cor20}) end end ==> module 'foo' ['t'/4] attributes [] 't'/4 = fun (_cor14,Sub0,_cor15,_cor16) -> let Ssa = call 'erlang':'get' ('foo') in let _fol0 = {'ssa',_cor14,Sub0,_cor15,_cor16} in let _rec11 = call 'erlang':'+' (_cor14, 1) in let _cor4 = call 'erlang':'setelement' (2, _fol0, _rec11) in let NewReg = {'tmp',_cor14} in {NewReg,_cor4,Ssa} end
-rw-r--r--lib/compiler/src/sys_core_fold.erl78
1 files changed, 77 insertions, 1 deletions
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index d1eec9e347..c45c7aa1de 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -349,7 +349,12 @@ expr(#c_case{}=Case0, Ctxt, Sub) ->
Case = Case1#c_case{arg=Arg2,clauses=Cs2},
warn_no_clause_match(Case1, Case),
Expr = eval_case(Case, Sub),
- bsm_an(Expr);
+ case move_case_into_arg(Case, Sub) of
+ impossible ->
+ bsm_an(Expr);
+ Other ->
+ expr(Other, Ctxt, sub_new_preserve_types(Sub))
+ end;
Other ->
expr(Other, Ctxt, Sub)
end;
@@ -2571,6 +2576,77 @@ opt_simple_let_2(Let, Vs0, Arg0, Body, value, Sub) ->
value, Sub)
end.
+move_case_into_arg(#c_case{arg=#c_let{vars=OuterVars0,arg=OuterArg,
+ body=InnerArg0}=Outer,
+ clauses=InnerClauses}=Inner, Sub) ->
+ %%
+ %% case let <OuterVars> = <OuterArg> in <InnerArg> of
+ %% <InnerClauses>
+ %% end
+ %%
+ %% ==>
+ %%
+ %% let <OuterVars> = <OuterArg>
+ %% in case <InnerArg> of <InnerClauses> end
+ %%
+ ScopeSub0 = sub_subst_scope(Sub#sub{t=[]}),
+ {OuterVars,ScopeSub} = pattern_list(OuterVars0, ScopeSub0),
+ InnerArg = body(InnerArg0, ScopeSub),
+ Outer#c_let{vars=OuterVars,arg=OuterArg,
+ body=Inner#c_case{arg=InnerArg,clauses=InnerClauses}};
+move_case_into_arg(#c_case{arg=#c_case{arg=OuterArg,
+ clauses=[OuterCa0,OuterCb]}=Outer,
+ clauses=InnerClauses}=Inner0, Sub) ->
+ case is_failing_clause(OuterCb) of
+ true ->
+ #c_clause{pats=OuterPats0,guard=OuterGuard0,
+ body=InnerArg0} = OuterCa0,
+ %%
+ %% case case <OuterArg> of
+ %% <OuterPats> when <OuterGuard> -> <InnerArg>
+ %% <OuterCb>
+ %% ...
+ %% end of
+ %% <InnerClauses>
+ %% end
+ %%
+ %% ==>
+ %%
+ %% case <OuterArg> of
+ %% <OuterPats> when <OuterGuard> ->
+ %% case <InnerArg> of <InnerClauses> end
+ %% <OuterCb>
+ %% end
+ %%
+ ScopeSub0 = sub_subst_scope(Sub#sub{t=[]}),
+ {OuterPats,ScopeSub} = pattern_list(OuterPats0, ScopeSub0),
+ OuterGuard = guard(OuterGuard0, ScopeSub),
+ InnerArg = body(InnerArg0, ScopeSub),
+ Inner = Inner0#c_case{arg=InnerArg,clauses=InnerClauses},
+ OuterCa = OuterCa0#c_clause{pats=OuterPats,guard=OuterGuard,
+ body=Inner},
+ Outer#c_case{arg=OuterArg,
+ clauses=[OuterCa,OuterCb]};
+ false ->
+ impossible
+ end;
+move_case_into_arg(#c_case{arg=#c_seq{arg=OuterArg,body=InnerArg}=Outer,
+ clauses=InnerClauses}=Inner, _Sub) ->
+ %%
+ %% case do <OuterArg> <InnerArg> of
+ %% <InnerClauses>
+ %% end
+ %%
+ %% ==>
+ %%
+ %% do <OuterArg>
+ %% case <InnerArg> of <InerClauses> end
+ %%
+ Outer#c_seq{arg=OuterArg,
+ body=Inner#c_case{arg=InnerArg,clauses=InnerClauses}};
+move_case_into_arg(_, _) ->
+ impossible.
+
%% In guards only, rewrite a case in a let argument like
%%
%% let <Var> = case <> of