tree 0e9f464de2ba2353eaa96be4bbcbeac377b6d46f
parent 183204f8eeeb3582971fe56a3721b200b8996559
author Pierre Langlois <pierre.langlois@arm.com> 1515004245 +0000
committer Commit Bot <commit-bot@chromium.org> 1516013161 +0000

[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}