From 223910b329751fbee36efe66ccd544e66dbe90f8 Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Fri, 26 Jan 2024 13:35:37 -0800
Subject: [PATCH] Reduce array allocations for literal arrays with splats and
 other args

Previously, a literal array with a splat and any other args resulted in
more than one array allocation:

```ruby
[1, *a]
[*a, 1]
[*a, *a]
[*a, 1, 2]

[*a, a]
[*a, 1, *a]
[*a, 1, a]
[*a, a, a]

[*a, a, *a]
[*a, 1, *a, 1]
[*a, 1, *a, *a]

[*a, a, *a, a]
```

This is because previously Ruby would use newarray and concatarray
to create the array, which both each allocate an array internally.

This changes the compilation to use concattoarray and pushtoarray,
which do not allocate arrays.  It also updates the peephole optimizer
to optimize the duparray/concattoarray sequence to
putobject/concattoarray, mirroring the existing duparray/concatarray
optimization.

These changes reduce the array allocations for the above examples to
a single array allocation, except for:

```
[*a, 1, a]
[*a, a, a]
```

The reason for this is because optimizing this case to only allocate
1 array requires changes to compile_array, which would currently
conflict with an unmerged pull request (#9721).  After that pull
request is merged, it should be possible to refactor things to only
allocate a 1 array for all literal arrays (or 2 for arrays with
keyword splats).
---
 compile.c | 37 ++++++++++++-------------------------
 1 file changed, 12 insertions(+), 25 deletions(-)

diff --git a/compile.c b/compile.c
index 71b657d9f2fcfb..4718ecc9e2b649 100644
--- a/compile.c
+++ b/compile.c
@@ -3377,15 +3377,15 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
     /*
      *  ...
      *  duparray [...]
-     *  concatarray
+     *  concatarray | concattoarray
      * =>
      *  ...
      *  putobject [...]
-     *  concatarray
+     *  concatarray | concattoarray
      */
     if (IS_INSN_ID(iobj, duparray)) {
         LINK_ELEMENT *next = iobj->link.next;
-        if (IS_INSN(next) && IS_INSN_ID(next, concatarray)) {
+        if (IS_INSN(next) && (IS_INSN_ID(next, concatarray) || IS_INSN_ID(next, concattoarray))) {
             iobj->insn_id = BIN(putobject);
         }
     }
@@ -4916,25 +4916,6 @@ compile_array(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *node, int pop
     return 1;
 }
 
-/* Compile an array containing the single element represented by node */
-static int
-compile_array_1(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *node)
-{
-    if (static_literal_node_p(node, iseq, false)) {
-        VALUE ary = rb_ary_hidden_new(1);
-        rb_ary_push(ary, static_literal_value(node, iseq));
-        OBJ_FREEZE(ary);
-
-        ADD_INSN1(ret, node, duparray, ary);
-    }
-    else {
-        CHECK(COMPILE_(ret, "array element", node, FALSE));
-        ADD_INSN1(ret, node, newarray, INT2FIX(1));
-    }
-
-    return 1;
-}
-
 static inline int
 static_literal_node_pair_p(const NODE *node, const rb_iseq_t *iseq)
 {
@@ -10412,7 +10393,7 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const no
         else {
             CHECK(COMPILE(ret, "argscat head", RNODE_ARGSCAT(node)->nd_head));
             CHECK(COMPILE(ret, "argscat body", RNODE_ARGSCAT(node)->nd_body));
-            ADD_INSN(ret, node, concatarray);
+            ADD_INSN(ret, node, concattoarray);
         }
         break;
       }
@@ -10425,8 +10406,14 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const no
         }
         else {
             CHECK(COMPILE(ret, "argspush head", RNODE_ARGSPUSH(node)->nd_head));
-            CHECK(compile_array_1(iseq, ret, RNODE_ARGSPUSH(node)->nd_body));
-            ADD_INSN(ret, node, concatarray);
+            const NODE *body_node = RNODE_ARGSPUSH(node)->nd_body;
+            if (static_literal_node_p(body_node, iseq, false)) {
+                ADD_INSN1(ret, body_node, putobject, static_literal_value(body_node, iseq));
+            }
+            else {
+                CHECK(COMPILE_(ret, "array element", body_node, FALSE));
+            }
+            ADD_INSN1(ret, node, pushtoarray, INT2FIX(1));
         }
         break;
       }