Changeset 247296 in webkit

Timestamp:

Jul 10, 2019 1:24:52 AM (5 years ago)

Author:

Tadeu Zagallo

Message:

Optimize join of large empty arrays
​https://bugs.webkit.org/show_bug.cgi?id=199636

Reviewed by Mark Lam.

JSTests:

• microbenchmarks/large-empty-array-join.js: Added.
• microbenchmarks/large-empty-array-join-resolve-rope.js: Added.

Source/JavaScriptCore:

Replicate the behavior of str.repeat(count) when performing new Array(count + 1).join(str).
I added two new microbenchmarks:

• large-empty-array-join, which does not use the result of the join and runs ~44x faster and uses ~18x less memory.
• large-empty-array-join-resolve-rope, which uses the result of the join and runs 2x faster.

baseline diff

large-empty-array-join 2713.9698+-72.7621 ^{61.2335+-10.4836} definitely 44.3217x faster
large-empty-array-join-resolve-string 26.5517+-0.3995 ^{12.9309+-0.5516} definitely 2.0533x faster

large-empty-array-join memory usage with baseline (dirty):

733012 kB current_mem
756824 kB lifetime_peak

large-empty-array-join memory usage with diff (dirty):

41904 kB current_mem
41972 kB lifetime_peak

Additionally, I ran JetStream2, sunspider and v8-spider and all were neutral.

• runtime/ArrayPrototype.cpp:

(JSC::fastJoin):

Location:

trunk

Files:

• JSTests/ChangeLog (modified) (1 diff)
• JSTests/microbenchmarks/large-empty-array-join-resolve-rope.js (added)
• JSTests/microbenchmarks/large-empty-array-join.js (added)
• Source/JavaScriptCore/ChangeLog (modified) (1 diff)
• Source/JavaScriptCore/runtime/ArrayPrototype.cpp (modified) (1 diff)

trunk/JSTests/ChangeLog

@@ +1 @@
+2019-07-10  Tadeu Zagallo  <tzagallo@apple.com>
+
+        Optimize join of large empty arrays
+        https://bugs.webkit.org/show_bug.cgi?id=199636
+
+        Reviewed by Mark Lam.
+
+        * microbenchmarks/large-empty-array-join.js: Added.
+        * microbenchmarks/large-empty-array-join-resolve-rope.js: Added.
+
 2019-07-06  Michael Saboff  <msaboff@apple.com>
 

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2019-07-10  Tadeu Zagallo  <tzagallo@apple.com>
+
+        Optimize join of large empty arrays
+        https://bugs.webkit.org/show_bug.cgi?id=199636
+
+        Reviewed by Mark Lam.
+
+        Replicate the behavior of `str.repeat(count)` when performing `new Array(count + 1).join(str)`.
+        I added two new microbenchmarks:
+        - large-empty-array-join, which does not use the result of the join and runs ~44x faster and uses ~18x less memory.
+        - large-empty-array-join-resolve-rope, which uses the result of the join and runs 2x faster.
+
+                                                    baseline                    diff
+        large-empty-array-join                2713.9698+-72.7621    ^     61.2335+-10.4836       ^ definitely 44.3217x faster
+        large-empty-array-join-resolve-string   26.5517+-0.3995     ^     12.9309+-0.5516        ^ definitely 2.0533x faster
+
+        large-empty-array-join memory usage with baseline (dirty):
+            733012 kB current_mem
+            756824 kB lifetime_peak
+
+        large-empty-array-join memory usage with diff (dirty):
+            41904 kB current_mem
+            41972 kB lifetime_peak
+
+        Additionally, I ran JetStream2, sunspider and v8-spider and all were neutral.
+
+        * runtime/ArrayPrototype.cpp:
+        (JSC::fastJoin):
+
 2019-07-08  Keith Miller  <keith_miller@apple.com>
 

trunk/Source/JavaScriptCore/runtime/ArrayPrototype.cpp

@@ -541 +541 @@
                 RELEASE_AND_RETURN(scope, repeatCharacter(state, separator.characters8()[0], length - 1));
             RELEASE_AND_RETURN(scope, repeatCharacter(state, separator.characters16()[0], length - 1));
+        default:
+            JSString* result = jsEmptyString(&state);
+            if (length <= 1)
+                return result;
+
+            JSString* operand = jsString(&vm, separator.toString());
+            RETURN_IF_EXCEPTION(scope, { });
+            unsigned count = length - 1;
+            for (;;) {
+                if (count & 1) {
+                    result = jsString(&state, result, operand);
+                    RETURN_IF_EXCEPTION(scope, { });
+                }
+                count >>= 1;
+                if (!count)
+                    return result;
+                operand = jsString(&state, operand, operand);
+                RETURN_IF_EXCEPTION(scope, { });
+            }
         }
         }