A64: Implement LMathFloorOfDiv and enable the instruction in hydrogen

A64: Implement LMathFloorOfDiv and enable the instruction in hydrogen

BUG=314606
R=ulan@chromium.org, baptiste.afsa@arm.com

Committed: https://code.google.com/p/v8/source/detail?r=18780

[jochen (gone - plz use gerrit), 2014-01-23 12:58:50]

plz review

[ulan, 2014-01-23 13:42:54]

lgtm, let's use 'A64:' as a cl prefix.

[jochen (gone - plz use gerrit), 2014-01-23 13:53:26]

Committed patchset #1 manually as r18780 (presubmit successful).

[baptiste.afsa1, 2014-01-23 13:54:19]

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64.cc
File src/a64/lithium-codegen-a64.cc (right):

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3627: __ Cmp(remainder, 0);
You can merge this two instructions into a Cbz.

[jbramley, 2014-01-23 14:15:12]

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64.cc
File src/a64/lithium-codegen-a64.cc (right):

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3596: const Register remainder =
ToRegister32(instr->temp());
We don't usually declare these as 'const'. If we're going to start doing that,
we should probably make a big change and do them all at once.

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3603: __ Cmp(left, kMinInt);
This will generate two instructions because cmp can't take the immediate
0x8000...00. Instead, use Cmp(left, 1); the V flag will be set if (and only if)
left was kMinInt. In context:

__ Cmp(left, 1);
__ Ccmp(right, -1, ZFlag, vs);
DeoptimizeIf(eq, ...);

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3619: __ Sdiv(result, left, right);
This can't cause an exception on ARM, so it can go right at the top to
speculatively calculate the result before we've checked for x/0, kMinInt/-1 and
the like.

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3621: __ Eor(remainder, left, Operand(right));
We have an implicit constructor for Operand (for simple registers and constants)
so you can just write 'right'.

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3626: __ Sub(remainder, remainder, left);
You can use Msub here instead of Mul and Sub:
__ Msub(remainder, result, right, left);

This produces a result with the opposite sign (left - result * right) but that's
fine for a compare-with-zero.

https://codereview.chromium.org/145273005/diff/1/src/a64/lithium-codegen-a64....
src/a64/lithium-codegen-a64.cc:3629: __ Sub(result, result, Operand(1));
We have an implicit constructor for Operand (for simple registers and constants)
so you can just write '1'.