MIPS: Array index computation dehoisting.

MIPS: Array index computation dehoisting.

Port r11596 (0cee9fca)

Original commit message:
Array index computation dehoisting.

When an array index (in an array access) is a simple "expression + constant", just embed the constant in the array access operation so that the full index expression is (potentially) no longer used and its live range can be much shorter.
This is effective in conjunction with array bounds check removal (otherwise the index is anyway used in the check).

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=11644

[Massi, 2012-05-24 09:01:31]

LGTM, I'll fix the two nits and commit it.
  Massi

https://chromiumcodereview.appspot.com/10442003/diff/1/src/mips/lithium-codeg...
File src/mips/lithium-codegen-mips.cc (right):

https://chromiumcodereview.appspot.com/10442003/diff/1/src/mips/lithium-codeg...
src/mips/lithium-codegen-mips.cc:2603: (constant_key << shift_size) +
additional_offset);
Nit: the line exceeds 80 chars.

https://chromiumcodereview.appspot.com/10442003/diff/1/src/mips/lithium-codeg...
src/mips/lithium-codegen-mips.cc:3644: __ Addu(scratch0(), key,
instr->additional_index());
You moved the declaration "Register scratch = scratch0();" just before this
block but you still use "scratch0()" in the Addu: wouldn't it be cleaner using
"scratch"?

[palfia, 2012-05-24 16:16:32]

Thanks for fixing these.

https://chromiumcodereview.appspot.com/10442003/diff/1/src/mips/lithium-codeg...
File src/mips/lithium-codegen-mips.cc (right):

https://chromiumcodereview.appspot.com/10442003/diff/1/src/mips/lithium-codeg...
src/mips/lithium-codegen-mips.cc:3644: __ Addu(scratch0(), key,
instr->additional_index());
On 2012/05/24 09:01:31, Massi wrote:
> You moved the declaration "Register scratch = scratch0();" just before this
> block but you still use "scratch0()" in the Addu: wouldn't it be cleaner using
> "scratch"?
Yes, it is much cleaner.