build: remove v8_typed_array_max_size_in_heap option

This was added in 16f86d6, based on
the assumption that otherwise, the memory behind `ArrayBuffer`
instances could be moved around on the heap while native code
holds references to it.

This does not match what V8 actually does (and also did at the time):

- The option/build variable was about always only about TypedArrays,
  not ArrayBuffers. Calls like `new ArrayBuffer(4)` call into C++
  regardless of the option value, but calls like `new Uint8Array(4)`
  would not call into C++ under V8 defaults.
- When first accessing a heap-allocated TypedArray’s `ArrayBuffer`,
  whether that is through the JS `.buffer` getter or the C++
  `ArrayBufferView::Buffer()` function, a copy of the contents is
  created using the ArrayBuffer allocator and stored as the
  (permanent, unmovable) backing store.

As a consequence, the memory returned by `ArrayBuffer::GetContents()`
is not moved around, because it is fixed once the `ArrayBuffer`
object itself first comes into explicit existence in any way.

Removing this build option significantly speeds up creation of typed
arrays from JS:

    $ ./node benchmark/compare.js --new ./node --old ./node-master --runs 10 --filter buffer-creation.js buffers | Rscript benchmark/compare.R
                                                                         confidence improvement accuracy (*)     (**)    (***)
     buffers/buffer-creation.js n=1024 len=10 type='buffer()'                  ***    593.66 %      ±28.64%  ±41.10%  ±60.36%
     buffers/buffer-creation.js n=1024 len=10 type='fast-alloc-fill'           ***    675.42 %      ±90.67% ±130.24% ±191.54%
     buffers/buffer-creation.js n=1024 len=10 type='fast-alloc'                ***    663.55 %      ±58.41%  ±83.87% ±123.29%
     buffers/buffer-creation.js n=1024 len=10 type='fast-allocUnsafe'                   3.10 %       ±9.63%  ±13.22%  ±18.07%
     buffers/buffer-creation.js n=1024 len=10 type='slow-allocUnsafe'                   4.67 %       ±5.55%   ±7.77%  ±10.97%
     buffers/buffer-creation.js n=1024 len=10 type='slow'                              -2.48 %       ±4.47%   ±6.12%   ±8.34%
     buffers/buffer-creation.js n=1024 len=1024 type='buffer()'                        -1.91 %       ±4.71%   ±6.45%   ±8.79%
     buffers/buffer-creation.js n=1024 len=1024 type='fast-alloc-fill'                 -1.34 %       ±7.53%  ±10.33%  ±14.10%
     buffers/buffer-creation.js n=1024 len=1024 type='fast-alloc'                       0.52 %       ±5.00%   ±6.87%   ±9.40%
     buffers/buffer-creation.js n=1024 len=1024 type='fast-allocUnsafe'                 0.39 %       ±5.65%   ±7.78%  ±10.67%
     buffers/buffer-creation.js n=1024 len=1024 type='slow-allocUnsafe'                -0.13 %       ±5.68%   ±7.83%  ±10.77%
     buffers/buffer-creation.js n=1024 len=1024 type='slow'                            -5.07 %       ±7.15%   ±9.80%  ±13.35%
     buffers/buffer-creation.js n=1024 len=2048 type='buffer()'                         0.57 %       ±2.70%   ±3.74%   ±5.16%
     buffers/buffer-creation.js n=1024 len=2048 type='fast-alloc-fill'                 -1.60 %       ±4.96%   ±6.79%   ±9.25%
     buffers/buffer-creation.js n=1024 len=2048 type='fast-alloc'                       1.29 %       ±3.79%   ±5.20%   ±7.09%
     buffers/buffer-creation.js n=1024 len=2048 type='fast-allocUnsafe'                 2.73 %       ±8.79%  ±12.05%  ±16.41%
     buffers/buffer-creation.js n=1024 len=2048 type='slow-allocUnsafe'                -0.99 %       ±6.27%   ±8.65%  ±11.91%
     buffers/buffer-creation.js n=1024 len=2048 type='slow'                            -5.98 %       ±6.24%   ±8.71%  ±12.20%
     buffers/buffer-creation.js n=1024 len=4096 type='buffer()'                        -1.75 %       ±3.48%   ±4.78%   ±6.56%
     buffers/buffer-creation.js n=1024 len=4096 type='fast-alloc-fill'                 -3.18 %       ±3.97%   ±5.45%   ±7.45%
     buffers/buffer-creation.js n=1024 len=4096 type='fast-alloc'                       2.05 %       ±4.05%   ±5.58%   ±7.65%
     buffers/buffer-creation.js n=1024 len=4096 type='fast-allocUnsafe'                 1.44 %       ±5.51%   ±7.63%  ±10.57%
     buffers/buffer-creation.js n=1024 len=4096 type='slow-allocUnsafe'          *     -4.77 %       ±4.30%   ±5.90%   ±8.06%
     buffers/buffer-creation.js n=1024 len=4096 type='slow'                            -3.31 %       ±6.38%   ±8.86%  ±12.34%
     buffers/buffer-creation.js n=1024 len=8192 type='buffer()'                         0.06 %       ±2.70%   ±3.77%   ±5.31%
     buffers/buffer-creation.js n=1024 len=8192 type='fast-alloc-fill'                 -1.20 %       ±3.30%   ±4.53%   ±6.17%
     buffers/buffer-creation.js n=1024 len=8192 type='fast-alloc'                      -1.46 %       ±2.75%   ±3.84%   ±5.38%
     buffers/buffer-creation.js n=1024 len=8192 type='fast-allocUnsafe'                 1.27 %       ±4.69%   ±6.49%   ±8.98%
     buffers/buffer-creation.js n=1024 len=8192 type='slow-allocUnsafe'                -1.68 %       ±3.30%   ±4.62%   ±6.49%
     buffers/buffer-creation.js n=1024 len=8192 type='slow'                            -2.49 %       ±3.24%   ±4.44%   ±6.07%
     (Re-running the outlier with 30 runs instead of 10:)
     buffers/buffer-creation.js n=1024 len=4096 type='slow-allocUnsafe'                 2.06 %       ±2.39%   ±3.19%   ±4.15%

The performance gains effect are undone once native code accesses
the underlying ArrayBuffer, but then again that a) does not happen for
all TypedArrays, and b) it should also make sense to look into using
`ArrayBufferView::CopyContents()` in some places, which is made
specifically to avoid such a performance impact and allows us to
use the benefits of heap-allocated typed arrays.

Refs: 16f86d6
Refs: #2893
Refs: 74178a5#commitcomment-13250880
Refs: http://logs.libuv.org/node-dev/2015-09-15

PR-URL: #26301
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: addaleax

configure.py

@@ -1179,10 +1179,6 @@ def configure_v8(o):
   o['variables']['node_use_bundled_v8'] = b(not options.without_bundled_v8)
   o['variables']['force_dynamic_crt'] = 1 if options.shared else 0
   o['variables']['node_enable_d8'] = b(options.enable_d8)
-  # Unconditionally force typed arrays to allocate outside the v8 heap. This
-  # is to prevent memory pointers from being moved around that are returned by
-  # Buffer::Data().
-  o['variables']['v8_typed_array_max_size_in_heap'] = 0
   if options.enable_d8:
     o['variables']['test_isolation_mode'] = 'noop'  # Needed by d8.gyp.
   if options.without_bundled_v8 and options.enable_d8: