From 7b64965d7a22d2250d3c6582a6d1737ca325a8dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Wed, 23 Aug 2017 07:12:52 +0200
Subject: arith_instrs.tab: Clean up bsl/bsr

Eliminate the all-purpose variable 'ires'. Replace it with several
variables used that are used for their specific purpose. Narrow
the scope of the variables.

Do this to improve readability. It is not expected that it should
any impact on performance.
---
 erts/emulator/beam/arith_instrs.tab | 49 ++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/erts/emulator/beam/arith_instrs.tab b/erts/emulator/beam/arith_instrs.tab
index 224945287b..67cd7c6a2a 100644
--- a/erts/emulator/beam/arith_instrs.tab
+++ b/erts/emulator/beam/arith_instrs.tab
@@ -226,9 +226,6 @@ i_bsr := shift.setup_bsr.execute;
 shift.head() {
     Eterm Op1, Op2;
     Sint shift_left_count;
-    Sint ires;
-    Eterm* bigp;
-    Eterm tmp_big[2];
 }
 
 shift.setup_bsr(Src1, Src2) {
@@ -272,35 +269,37 @@ shift.setup_bsl(Src1, Src2) {
 }
 
 shift.execute(Fail, Live, Dst) {
+    Uint big_words_needed;
+
     if (is_small(Op1)) {
-        ires = signed_val(Op1);
-        if (shift_left_count == 0 || ires == 0) {
+        Sint int_res = signed_val(Op1);
+        if (shift_left_count == 0 || int_res == 0) {
             if (is_not_integer(Op2)) {
                 goto shift_error;
             }
-            if (ires == 0) {
+            if (int_res == 0) {
                 $Dst = Op1;
                 $NEXT0();
             }
         } else if (shift_left_count < 0)  { /* Right shift */
+            Eterm bsr_res;
             shift_left_count = -shift_left_count;
             if (shift_left_count >= SMALL_BITS-1) {
-                $Dst = (ires < 0) ? SMALL_MINUS_ONE : SMALL_ZERO;
+                bsr_res = (int_res < 0) ? SMALL_MINUS_ONE : SMALL_ZERO;
             } else {
-                $Dst = make_small(ires >> shift_left_count);
+                bsr_res = make_small(int_res >> shift_left_count);
             }
+            $Dst = bsr_res;
             $NEXT0();
         } else if (shift_left_count < SMALL_BITS-1) { /* Left shift */
-            if ((ires > 0 &&
-                 ((~(Uint)0 << ((SMALL_BITS-1)-shift_left_count)) &
-                  ires) == 0) ||
-                ((~(Uint)0 << ((SMALL_BITS-1)-shift_left_count)) &
-                 ~ires) == 0) {
-                $Dst = make_small(ires << shift_left_count);
+            if ((int_res > 0 &&
+                 ((~(Uint)0 << ((SMALL_BITS-1)-shift_left_count)) & int_res) == 0) ||
+                ((~(Uint)0 << ((SMALL_BITS-1)-shift_left_count)) & ~int_res) == 0) {
+                $Dst = make_small(int_res << shift_left_count);
                 $NEXT0();
             }
         }
-        ires = 1;               /* big_size(small_to_big(Op1)) */
+        big_words_needed = 1;   /* big_size(small_to_big(Op1)) */
         goto big_shift;
     } else if (is_big(Op1)) {
         if (shift_left_count == 0) {
@@ -310,20 +309,21 @@ shift.execute(Fail, Live, Dst) {
             $Dst = Op1;
             $NEXT0();
         }
-        ires = big_size(Op1);
+        big_words_needed = big_size(Op1);
 
     big_shift:
         if (shift_left_count > 0) {	/* Left shift. */
-            ires += (shift_left_count / D_EXP);
+            big_words_needed += (shift_left_count / D_EXP);
         } else {	/* Right shift. */
-            if (ires <= (-shift_left_count / D_EXP)) {
-                ires = 3;       /* ??? */
+            if (big_words_needed <= (-shift_left_count / D_EXP)) {
+                big_words_needed = 3;       /* ??? */
             } else {
-                ires -= (-shift_left_count / D_EXP);
+                big_words_needed -= (-shift_left_count / D_EXP);
             }
         }
         {
-            ires = BIG_NEED_SIZE(ires+1);
+            Eterm tmp_big[2];
+            Sint big_need_size = BIG_NEED_SIZE(big_words_needed+1);
 
             /*
              * Slightly conservative check the size to avoid
@@ -331,15 +331,14 @@ shift.execute(Fail, Live, Dst) {
              * clearly would overflow the arity in the header
              * word.
              */
-            if (ires-8 > BIG_ARITY_MAX) {
+            if (big_need_size-8 > BIG_ARITY_MAX) {
                 $SYSTEM_LIMIT($Fail);
             }
-            $GC_TEST_PRESERVE(ires+1, $Live, Op1);
+            $GC_TEST_PRESERVE(big_need_size+1, $Live, Op1);
             if (is_small(Op1)) {
                 Op1 = small_to_big(signed_val(Op1), tmp_big);
             }
-            bigp = HTOP;
-            Op1 = big_lshift(Op1, shift_left_count, bigp);
+            Op1 = big_lshift(Op1, shift_left_count, HTOP);
             if (is_big(Op1)) {
                 HTOP += bignum_header_arity(*HTOP) + 1;
             }
-- 
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