diff options
Diffstat (limited to 'lib/compiler/src/sys_core_fold.erl')
| -rw-r--r-- | lib/compiler/src/sys_core_fold.erl | 43 |
1 files changed, 39 insertions, 4 deletions
diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl index c45c7aa1de..e2b9213891 100644 --- a/lib/compiler/src/sys_core_fold.erl +++ b/lib/compiler/src/sys_core_fold.erl @@ -305,6 +305,10 @@ expr(#c_let{}=Let, Ctxt, Sub) -> %% Now recursively re-process the new expression. expr(Expr, Ctxt, sub_new_preserve_types(Sub)) end; +expr(#c_letrec{body=#c_var{}}=Letrec, effect, _Sub) -> + %% This is named fun in an 'effect' context. Warn and ignore. + add_warning(Letrec, useless_building), + void(); expr(#c_letrec{defs=Fs0,body=B0}=Letrec, Ctxt, Sub) -> Fs1 = map(fun ({Name,Fb}) -> {Name,expr(Fb, {letrec,Ctxt}, Sub)} @@ -1941,14 +1945,45 @@ opt_bool_case_guard(Arg, [#c_clause{pats=[#c_literal{val=false}]}=Fc,Tc]) -> %% last clause is guaranteed to match so if there is only one clause %% with a pattern containing only variables then rewrite to a let. -eval_case(#c_case{arg=E,clauses=[#c_clause{pats=Ps0,body=B}]}, Sub) -> +eval_case(#c_case{arg=E,clauses=[#c_clause{pats=Ps0, + guard=#c_literal{val=true}, + body=B}]}=Case, Sub) -> Es = case cerl:is_c_values(E) of true -> cerl:values_es(E); false -> [E] end, - {true,Bs} = cerl_clauses:match_list(Ps0, Es), - {Ps,As} = unzip(Bs), - expr(#c_let{vars=Ps,arg=core_lib:make_values(As),body=B}, sub_new(Sub)); + %% Consider: + %% + %% case SomeSideEffect() of + %% X=Y -> ... + %% end + %% + %% We must not rewrite it to: + %% + %% let <X,Y> = <SomeSideEffect(),SomeSideEffect()> in ... + %% + %% because SomeSideEffect() would be evaluated twice. + %% + %% Instead we must evaluate the case expression in an outer let + %% like this: + %% + %% let NewVar = SomeSideEffect() in + %% let <X,Y> = <NewVar,NewVar> in ... + %% + Vs = make_vars([], length(Es)), + case cerl_clauses:match_list(Ps0, Vs) of + {false,_} -> + %% This can only happen if the Core Erlang code is + %% handwritten or generated by another code generator + %% than v3_core. Assuming that the Core Erlang program + %% is correct, the clause will always match at run-time. + Case; + {true,Bs} -> + {Ps,As} = unzip(Bs), + InnerLet = cerl:c_let(Ps, core_lib:make_values(As), B), + Let = cerl:c_let(Vs, E, InnerLet), + expr(Let, sub_new(Sub)) + end; eval_case(Case, _) -> Case. %% case_opt(CaseArg, [Clause]) -> {CaseArg,[Clause]}. |