Introduce a new core pass called sys_core_alias

The goal of this pass is to find values that are built from
patterns and generate aliases for those values to remove
pressure from the GC. For example, this code:

   example({ok, Val}) ->
       {ok, Val}.

shall become:

   example({ok, Val} = Tuple) ->
       Tuple.

Currently this pass aliases tuple and cons nodes made of literals,
variables and other cons. The tuple/cons may appear anywhere in the
pattern and it will be aliased if used later on.

Notice a tuple/cons made only of literals is not aliased as it may
be part of the literal pool.

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/compiler/src/compile.erl b/lib/compiler/src/compile.erl
index aa2d224bb4..ec7e7aed14 100644
--- a/lib/compiler/src/compile.erl
+++ b/lib/compiler/src/compile.erl
@@ -706,14 +706,16 @@ core_passes() ->
       [{unless,no_copt,
        [{core_old_inliner,fun test_old_inliner/1,fun core_old_inliner/2},
 	{iff,doldinline,{listing,"oldinline"}},
-	{pass,sys_core_fold},
+	{unless,no_fold,{pass,sys_core_fold}},
 	{iff,dcorefold,{listing,"corefold"}},
 	{core_inline_module,fun test_core_inliner/1,fun core_inline_module/2},
 	{iff,dinline,{listing,"inline"}},
         {core_fold_after_inlining,fun test_any_inliner/1,
          fun core_fold_module_after_inlining/2},
+        {iff,dcopt,{listing,"copt"}},
+        {unless,no_alias,{pass,sys_core_alias}},
+        {iff,dalias,{listing,"core_alias"}},
 	?pass(core_transforms)]},
-       {iff,dcopt,{listing,"copt"}},
        {iff,'to_core',{done,"core"}}]}
      | kernel_passes()].
 
@@ -1921,6 +1923,7 @@ pre_load() ->
 	 erl_lint,
 	 erl_parse,
 	 erl_scan,
+	 sys_core_alias,
 	 sys_core_bsm,
 	 sys_core_dsetel,
 	 sys_core_fold,