Add beam_ssa_dead.erl

Add beam_ssa_dead to perform the main optimizations done
by beam_dead:

* Shortcut branches that jump to another block with a branch.
If it can be seen that the second branch will always branch
to a specific block, replace the target of the first branch.

* Combined nested sequences of '=:=' tests and switch
instructions operating on the same variable to a single switch.

Diffing the compiler output, it seems that beam_ssa_dead finds
many more opportunities for optimizations than beam_dead,
although it does not find all opportunities that beam_dead does.
In total, beam_ssa_dead is such improvement over beam_dead that
there is no reason to keep beam_dead as well as beam_ssa_dead.

Note that beam_ssa_dead does not attempt to optimize away
redundant bs_context_binary instructions, because that instruction
will be superseded by new instructions in the near future.

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/compiler/test/match_SUITE.erl b/lib/compiler/test/match_SUITE.erl
index 46b543728d..229c3093d7 100644
--- a/lib/compiler/test/match_SUITE.erl
+++ b/lib/compiler/test/match_SUITE.erl
@@ -446,6 +446,7 @@ letify_guard(A, B) ->
 selectify(Config) when is_list(Config) ->
     integer = sel_different_types({r,42}),
     atom = sel_different_types({r,forty_two}),
+    float = sel_different_types({r,100.0}),
     none = sel_different_types({r,18}),
     {'EXIT',_} = (catch sel_different_types([a,b,c])),
 
@@ -456,12 +457,15 @@ selectify(Config) when is_list(Config) ->
     integer42 = sel_same_value2(42),
     integer43 = sel_same_value2(43),
     error = sel_same_value2(44),
+
     ok.
 
 sel_different_types({r,_}=T) when element(2, T) =:= forty_two ->
     atom;
 sel_different_types({r,_}=T) when element(2, T) =:= 42 ->
     integer;
+sel_different_types({r,_}=T) when element(2, T) =:= 100.0 ->
+    float;
 sel_different_types({r,_}) ->
     none.