MIPS: Fix Subu and add optimization

MIPS: Fix Subu and add optimization

For int16 imm values Subu would emit addiu with -imm value, but doing
this with min_int16 would overflow and produce incorrect result. This is
fixed by checking if -imm is int16. A test for this case is created.

An optimization is also added for values imm where we cannot just emit
addiu and loading -imm to a register takes one instruction using ori.
Then instead of loading imm with lui;ori and subtracting with subu, we
can load -imm with ori and add with addu.

BUG=
TEST=cctest/test-assembler-mips/Subu

Review-Url: https://codereview.chromium.org/2845043002
Cr-Commit-Position: refs/heads/master@{#44932}
Committed: https://chromium.googlesource.com/v8/v8/+/de14ba9fd2292a20f6b14d9cb7e0a625b855cfe0

[miran.karic, 2017-04-27 08:53:42]

miran.karic@imgtec.com changed reviewers:
+ dusan.simicic@imgtec.com, ilija.pavlovic@imgtec.com,
ivica.bogosavljevic@imgtec.com

[miran.karic, 2017-04-27 08:53:43]

PTAL

[Ilija.Pavlovic1, 2017-04-27 09:16:18]

ilija.pavlovic@imgtec.com changed reviewers:
+ Ilija.Pavlovic@imgtec.com

[Ilija.Pavlovic1, 2017-04-27 09:16:19]

lgtm

[ivica.bogosavljevic, 2017-04-27 09:18:27]

ivica.bogosavljevic@imgtec.com changed reviewers:
- Ilija.Pavlovic@imgtec.com

[ivica.bogosavljevic, 2017-04-27 09:18:28]

https://codereview.chromium.org/2845043002/diff/1/test/cctest/test-assembler-...
File test/cctest/test-assembler-mips.cc (right):

https://codereview.chromium.org/2845043002/diff/1/test/cctest/test-assembler-...
test/cctest/test-assembler-mips.cc:5528: Label start1, start2, start3, start4,
start5, start6;
I think it would be more readable to create an array of [label, operand,
instruction_count] and then loop over the array instead of having the same code
six times.

[miran.karic, 2017-04-27 11:05:06]

PTAL

https://codereview.chromium.org/2845043002/diff/1/test/cctest/test-assembler-...
File test/cctest/test-assembler-mips.cc (right):

https://codereview.chromium.org/2845043002/diff/1/test/cctest/test-assembler-...
test/cctest/test-assembler-mips.cc:5528: Label start1, start2, start3, start4,
start5, start6;
On 2017/04/27 09:18:28, ivica.bogosavljevic wrote:
> I think it would be more readable to create an array of [label, operand,
> instruction_count] and then loop over the array instead of having the same
code
> six times.

Done.

[ivica.bogosavljevic, 2017-04-27 12:30:55]

lgtm

[miran.karic, 2017-04-27 12:32:29]

The CQ bit was checked by miran.karic@imgtec.com

[miran.karic, 2017-04-27 12:32:29]

The patchset sent to the CQ was uploaded after l-g-t-m from
Ilija.Pavlovic@imgtec.com
Link to the patchset: https://codereview.chromium.org/2845043002/#ps40001
(title: "Move testcases to an array")

[commit-bot: I haz the power, 2017-04-27 12:32:35]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-27 12:56:50]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1493296349083580,
"parent_rev": "33b0b710b1f646cf6a8b9e8dac54c76be458bff3", "commit_rev":
"de14ba9fd2292a20f6b14d9cb7e0a625b855cfe0"}

[commit-bot: I haz the power, 2017-04-27 12:56:56]

Description was changed from

==========
MIPS: Fix Subu and add optimization

For int16 imm values Subu would emit addiu with -imm value, but doing
this with min_int16 would overflow and produce incorrect result. This is
fixed by checking if -imm is int16. A test for this case is created.

An optimization is also added for values imm where we cannot just emit
addiu and loading -imm to a register takes one instruction using ori.
Then instead of loading imm with lui;ori and subtracting with subu, we
can load -imm with ori and add with addu.

BUG=
TEST=cctest/test-assembler-mips/Subu
==========

to

==========
MIPS: Fix Subu and add optimization

For int16 imm values Subu would emit addiu with -imm value, but doing
this with min_int16 would overflow and produce incorrect result. This is
fixed by checking if -imm is int16. A test for this case is created.

An optimization is also added for values imm where we cannot just emit
addiu and loading -imm to a register takes one instruction using ori.
Then instead of loading imm with lui;ori and subtracting with subu, we
can load -imm with ori and add with addu.

BUG=
TEST=cctest/test-assembler-mips/Subu

Review-Url: https://codereview.chromium.org/2845043002
Cr-Commit-Position: refs/heads/master@{#44932}
Committed:
https://chromium.googlesource.com/v8/v8/+/de14ba9fd2292a20f6b14d9cb7e0a625b85...
==========

[commit-bot: I haz the power, 2017-04-27 12:56:57]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/v8/v8/+/de14ba9fd2292a20f6b14d9cb7e0a625b85...