From c91c523f1ca58644267402325b6fb59d65049829 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Magnus=20L=C3=A5ng?= <margnus1@telia.com>
Date: Wed, 9 Nov 2016 18:47:12 +0100
Subject: hipe_rtl: drop alub dest when unused

---
 lib/hipe/rtl/hipe_rtl.erl | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'lib/hipe/rtl/hipe_rtl.erl')

diff --git a/lib/hipe/rtl/hipe_rtl.erl b/lib/hipe/rtl/hipe_rtl.erl
index e4e857ec43..d39969a0ed 100644
--- a/lib/hipe/rtl/hipe_rtl.erl
+++ b/lib/hipe/rtl/hipe_rtl.erl
@@ -334,6 +334,7 @@
 	 defines/1,
 	 redirect_jmp/3,
 	 is_safe/1,
+	 reduce_unused/1,
 	 %% highest_var/1,
 	 pp/1,
 	 pp/2,
@@ -1314,6 +1315,24 @@ is_safe(Instr) ->
     #switch{} -> false %% Maybe this is safe...
   end.
 
+%% @spec reduce_unused(rtl_instruction())
+%%           -> false | [rtl_instruction()].
+%%
+%% @doc Produces a simplified instruction sequence that is equivalent to [Instr]
+%% under the assumption that all results of Instr are unused, or 'false' if
+%% there is no such sequence (other than [Instr] itself).
+
+reduce_unused(Instr) ->
+  case Instr of
+    #alub{dst=Dst} when Dst =/= [] ->
+      [Instr#alub{dst=[]}];
+    _ ->
+      case is_safe(Instr) of
+	true -> [];
+	false -> false
+      end
+  end.
+
 %%
 %% True if argument is an alu-operator
 %%
-- 
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