From ffa22bf1013c7dfeeb7bbf846983dfe39deb7e52 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 15 Mar 2019 07:47:39 +0100
Subject: Optimize some common uses of '+' and '-'

---
 erts/emulator/beam/beam_load.c | 18 ++++++++++++++++++
 erts/emulator/beam/ops.tab     | 12 ++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

(limited to 'erts/emulator/beam')

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 5961b7d743..c2a54c85ce 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -3679,6 +3679,24 @@ gen_increment_from_minus(LoaderState* stp, GenOpArg Reg,
     return op;
 }
 
+static GenOp*
+gen_plus_from_minus(LoaderState* stp, GenOpArg Fail, GenOpArg Live,
+                    GenOpArg Src, GenOpArg Integer, GenOpArg Dst)
+{
+    GenOp* op;
+
+    NEW_GENOP(stp, op);
+    GENOP_NAME_ARITY(op, gen_plus, 5);
+    op->next = NULL;
+    op->a[0] = Fail;
+    op->a[1] = Live;
+    op->a[2] = Src;
+    op->a[3].type = TAG_i;
+    op->a[3].val = -Integer.val;
+    op->a[4] = Dst;
+    return op;
+}
+
 /*
  * Test whether the negation of the given number is small.
  */
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index d60e6d6b53..649d861c80 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -1613,6 +1613,11 @@ gen_minus p Live Reg=d Int=i Dst | negation_is_small(Int) => \
 # Arithmetic instructions.
 #
 
+# It is OK to swap arguments for '+' in a guard. It is also
+# OK to turn minus into plus in a guard.
+gen_plus Fail=f Live S1=c S2 Dst => i_plus S2 S1 Fail Dst
+gen_minus Fail=f Live S1 S2=i Dst => gen_plus_from_minus(Fail, Live, S1, S2, Dst)
+
 gen_plus Fail Live S1 S2 Dst => i_plus S1 S2 Fail Dst
 
 gen_minus Fail Live S1 S2 Dst => i_minus S1 S2 Fail Dst
@@ -1646,10 +1651,13 @@ gc_bif1 Fail Live u$bif:erlang:bnot/1 Src Dst=d => i_int_bnot Fail Src Dst
 
 i_increment rxy W d
 
-i_plus x xy j? d
-i_plus s s  j? d
+# Handle unoptimized code.
+i_plus S1=c S2=c Fail Dst => move S1 x | i_plus x S2 Fail Dst
+
+i_plus xy xyc j? d
 
 i_minus x x j? d
+i_minus c x j? d
 i_minus s s j? d
 
 i_times j? s s d
-- 
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