From 43b6fe94007525ec1fa424da57b86d8d5c624ff7 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@ruby-lang.org>
Date: Thu, 14 May 2020 12:28:31 -0700
Subject: [PATCH] Speed up setting instance variables
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This patch speeds up setting instance variables somewhat.  Here is the
benchmark:

```ruby
class IVSetter
  def init
    @a = @b = @c = @d = nil
  end
end

obj = IVSetter.new

require "benchmark/ips"

Benchmark.ips do |x|
  x.report("init") do
    obj.init
  end
end
```

Before this patch:

```
[aaron@tc-lan-adapter ~/g/ruby (master)]$ ./ruby -v ../y.rb
ruby 2.8.0dev (2020-05-13T15:51:04Z master 65c5a39578) [x86_64-darwin19]
Warming up --------------------------------------
                init     1.324M i/100ms
Calculating -------------------------------------
                init     13.034M (± 1.6%) i/s -     66.210M in   5.080905s
```

After this patch:

```
[aaron@tc-lan-adapter ~/g/ruby (faster-ivar-set)]$ ./ruby -v ../y.rb
ruby 2.8.0dev (2020-05-14T19:33:13Z faster-ivar-set 60cfbb9d7e) [x86_64-darwin19]
Warming up --------------------------------------
                init     1.456M i/100ms
Calculating -------------------------------------
                init     14.599M (± 1.5%) i/s -     74.270M in   5.088467s
```

This speeds up ivar sets because we can reduce redundant checks.
`ROBJECT_NUMIV` and `ROBJECT_IVPTR` both check that the object is a
`T_OBJECT`, but the caller (`vm_setivar`) already knows this is a
`T_OBJECT` (otherwise this branch wouldn't be executing).

Secondly, both `ROBJECT_IVPTR` and `ROBJECT_NUMIV` check flags for
`ROBJECT_EMBED`.  We can reduce the check to just once.

I thought the C compiler would be smart enough to eliminate these
redundant checks, but after reading the assembly code it's clear that
the checks are being performed multiple times.
---
 vm_insnhelper.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 4d1d4ea0f9a15a..6796c0b7f8c552 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1142,10 +1142,21 @@ vm_setivar(VALUE obj, ID id, VALUE val, IVC ic, const struct rb_callcache *cc, i
 	if (LIKELY(
 	    (!is_attr && RB_DEBUG_COUNTER_INC_UNLESS(ivar_set_ic_miss_serial, ic->ic_serial == RCLASS_SERIAL(klass))) ||
 	    ( is_attr && RB_DEBUG_COUNTER_INC_UNLESS(ivar_set_ic_miss_unset, vm_cc_attr_index(cc) > 0)))) {
-	    VALUE *ptr = ROBJECT_IVPTR(obj);
+            VALUE *ptr;
+            uint32_t numiv;
+            struct RObject *const robj = ROBJECT(obj);
+
+            if (RB_FL_ANY_RAW(obj, ROBJECT_EMBED)) {
+                ptr = robj->as.ary;
+                numiv = ROBJECT_EMBED_LEN_MAX;
+            } else {
+                ptr = robj->as.heap.ivptr;
+                numiv = robj->as.heap.numiv;
+            }
+
 	    index = !is_attr ? ic->index : vm_cc_attr_index(cc)-1;
 
-	    if (RB_DEBUG_COUNTER_INC_UNLESS(ivar_set_ic_miss_oorange, index < ROBJECT_NUMIV(obj))) {
+	    if (RB_DEBUG_COUNTER_INC_UNLESS(ivar_set_ic_miss_oorange, index < numiv)) {
 		RB_OBJ_WRITE(obj, &ptr[index], val);
 		RB_DEBUG_COUNTER_INC(ivar_set_ic_hit);
 		return val; /* inline cache hit */