[turbofan] Lower NumberConstant nodes to IntPtrConstant.

If a NumberConstant can be represented as a Smi, then lower it to a
IntPtrConstant node during simplified lowering. Thanks to this, all backends can
match Smi values that can also be encoded as immediates in the instruction
selector. Additionally, we can apply the same lowering to the CodeAssembler for
the snapshot.

As a result, we can remove `mov` instructions generated because Int32Matcher and
Int64Matcher didn't not recognize Smis:

For 32-bit target, it's common for Smis also be immediates: "if (a < 100) {}"
~~~
mov r1, #200 -> cmp r0, #200
cmp r0, r1   -> blt <>
blt <>       ->
~~~

On Arm64 particularly, we lose opportunites to use `cbz`: "if (a == 0) {}"
~~~
movz x0, #0x0 -> cbz x1 <>
cmp x1, x0    ->
b.eq <>       ->
~~~

Overall, we do not see an impact on benchmarks such as webtooling. However, we
do see noteworthy code size reduction, from 0.5% to 1.5%.

Bug: 
Change-Id: I7fbb718ad51b9036c3514fa31c1326bdd6f2b0e6
Reviewed-on: https://chromium-review.googlesource.com/848814
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#50569}
6 files changed
tree: 0e9f464de2ba2353eaa96be4bbcbeac377b6d46f
  1. benchmarks/
  2. build_overrides/
  3. docs/
  4. gni/
  5. gypfiles/
  6. include/
  7. infra/
  8. samples/
  9. src/
  10. test/
  11. testing/
  12. third_party/
  13. tools/
  14. .clang-format
  15. .editorconfig
  16. .git-blame-ignore-revs
  17. .gitignore
  18. .gn
  19. .vpython
  20. .ycm_extra_conf.py
  21. AUTHORS
  22. BUILD.gn
  23. ChangeLog
  24. CODE_OF_CONDUCT.md
  25. codereview.settings
  26. DEPS
  27. LICENSE
  28. LICENSE.fdlibm
  29. LICENSE.strongtalk
  30. LICENSE.v8
  31. LICENSE.valgrind
  32. Makefile
  33. Makefile.android
  34. OWNERS
  35. PRESUBMIT.py
  36. README.md
  37. snapshot_toolchain.gni
  38. WATCHLISTS
README.md

V8 JavaScript Engine

V8 is Google's open source JavaScript engine.

V8 implements ECMAScript as specified in ECMA-262.

V8 is written in C++ and is used in Google Chrome, the open source browser from Google.

V8 can run standalone, or can be embedded into any C++ application.

V8 Project page: https://github.com/v8/v8/wiki

Getting the Code

Checkout depot tools, and run

    fetch v8

This will checkout V8 into the directory v8 and fetch all of its dependencies. To stay up to date, run

    git pull origin
    gclient sync

For fetching all branches, add the following into your remote configuration in .git/config:

    fetch = +refs/branch-heads/*:refs/remotes/branch-heads/*
    fetch = +refs/tags/*:refs/tags/*

Contributing

Please follow the instructions mentioned on the V8 wiki.