ARM: Implement fast code for ModI.

Implement fast code for the common cases of left hand sides that are less than three times larger as the right hand side and and right hand sides that are powers of two up and including 32.

In the covered special cases the result is computed directly, else the generic stub is called. The implementation deoptimizes only for mod 0 and if the result may be a negative zero.

BUG=none
TEST=none

[Søren Thygesen Gjesse, 2011-01-18 15:58:38]

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc
File src/arm/lithium-codegen-arm.cc (right):

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1041: // Try a few common cases before using the
generic stub.
Maybe extend this comment a bit (it took me some time to find out that you where
subtracting left 0 - 2 times from right).

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1049: if (i < kUnfolds - 1) __ sub(scratch, left,
right);
Shouldn't this be

__ sub(scratch, scratch, right, SetCC)

? Or maybe not, but when le is set will scratch not be negative (for positive
left/right)?

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1052: // Check for power of two on the right hand
side.
I think the code we have in GenericBinaryOpStub does this in fewer instructions.
It works on smis but should work for int32 as well.

  // Check for two positive smis.
  __ orr(smi_test_reg, lhs, Operand(rhs));
  __ tst(smi_test_reg, Operand(0x80000000u | kSmiTagMask));
  __ b(ne, &slow);
  // Check that rhs is a power of two and not zero.
  Register mask_bits = r3;
  __ sub(scratch, rhs, Operand(1), SetCC);
  __ b(mi, &slow);
  __ and_(mask_bits, rhs, Operand(scratch), SetCC);
  __ b(ne, &not_power_of_2);
  // Calculate power of two modulus.
  __ and_(result, lhs, Operand(scratch));

[Karl Klose, 2011-01-20 02:12:12]

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc
File src/arm/lithium-codegen-arm.cc (right):

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1041: // Try a few common cases before using the
generic stub.
On 2011/01/18 15:58:38, Søren Gjesse wrote:
> Maybe extend this comment a bit (it took me some time to find out that you
where
> subtracting left 0 - 2 times from right).

Done.

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1049: if (i < kUnfolds - 1) __ sub(scratch, left,
right);
Thanks for the catch.
On 2011/01/18 15:58:38, Søren Gjesse wrote:
> Shouldn't this be
> 
> __ sub(scratch, scratch, right, SetCC)
> 
> ? Or maybe not, but when le is set will scratch not be negative (for positive
> left/right)?

http://codereview.chromium.org/6331005/diff/1/src/arm/lithium-codegen-arm.cc#...
src/arm/lithium-codegen-arm.cc:1052: // Check for power of two on the right hand
side.
On 2011/01/18 15:58:38, Søren Gjesse wrote:
> I think the code we have in GenericBinaryOpStub does this in fewer
instructions.
> It works on smis but should work for int32 as well.
> 
>   // Check for two positive smis.
>   __ orr(smi_test_reg, lhs, Operand(rhs));
>   __ tst(smi_test_reg, Operand(0x80000000u | kSmiTagMask));
>   __ b(ne, &slow);
>   // Check that rhs is a power of two and not zero.
>   Register mask_bits = r3;
>   __ sub(scratch, rhs, Operand(1), SetCC);
>   __ b(mi, &slow);
>   __ and_(mask_bits, rhs, Operand(scratch), SetCC);
>   __ b(ne, &not_power_of_2);
>   // Calculate power of two modulus.
>   __ and_(result, lhs, Operand(scratch));

Done.

[Søren Thygesen Gjesse, 2011-01-20 07:17:57]

LGTM