Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

This patch adds support for missing integer division instruction sdiv, udiv, srem, urem.

R=stichnot@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=ae93eee8a07d3170fa6c233cbaf3675fe842b034

[obucinac, 2016-05-18 14:43:58]

Description was changed from

==========
Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

This patch adds support for missing integer division instruction sdiv, udiv,
srem, urem.
==========

to

==========
Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

This patch adds support for missing integer division instruction sdiv, udiv,
srem, urem.
==========

[obucinac, 2016-05-18 14:43:58]

obucinac@gmail.com changed reviewers:
+ sagar.thakur@imgtec.com, stichnot@chromium.org

[obucinac, 2016-05-18 15:03:12]

On 2016/05/18 14:43:58, obucinac wrote:
> mailto:obucinac@gmail.com changed reviewers:
> + mailto:sagar.thakur@imgtec.com, mailto:stichnot@chromium.org

I am a bit confused here. We are targeting MIPS32. With this change I am
producing DIV instruction with two operands, which exists on MIPS32. DIV with
three operands exists from MIPS32r6. My reference is "MIPS® Architecture For
Programmers, Volume II-A: The MIPS64® Instruction Set". However, when running
tests, I got error that there are not enough operands for DIV:

<stdin>:94:2: error: too few operands for instruction
        div     $a0, $a1

This makes me think that LLVM do not handle DIV properly. Or we are using MIPS32
string but we are targeting something else.

Please advise

[obucinac, 2016-05-18 16:41:12]

On 2016/05/18 15:03:33, obucinac wrote:

Patchset #2 contains workaround for DIV with three operands. When ZERO reg is
used as destination, produced encoding is the same as encoding of DIV with two
operands. Test are uploaded too. GNU assembler output for "div $1, $2" used as a
reference.

[Jim Stichnoth, 2016-05-18 18:13:23]

On 2016/05/18 15:03:12, obucinac wrote:
> On 2016/05/18 14:43:58, obucinac wrote:
> > mailto:obucinac@gmail.com changed reviewers:
> > + mailto:sagar.thakur@imgtec.com, mailto:stichnot@chromium.org
> 
> I am a bit confused here. We are targeting MIPS32. With this change I am
> producing DIV instruction with two operands, which exists on MIPS32. DIV with
> three operands exists from MIPS32r6. My reference is "MIPS® Architecture For
> Programmers, Volume II-A: The MIPS64® Instruction Set". However, when running
> tests, I got error that there are not enough operands for DIV:
> 
> <stdin>:94:2: error: too few operands for instruction
>         div     $a0, $a1
> 
> This makes me think that LLVM do not handle DIV properly. Or we are using
MIPS32
> string but we are targeting something else.
> 
> Please advise

This is interesting - I agree that either llvm-mc is broken, or we aren't using
the right triple/cpu/attr.

I tried the following command:

echo 'div $a0, $a1' | ../../../toolchain/linux_x86/pnacl_newlib_raw/bin/llvm-mc
-triple=mipsel -filetype=obj -o /dev/null -mcpu=mips32r6 -mattr=+mips32r6

and got the same "too few operands" error.  I couldn't come up with any other
-triple/-mcpu/-mattr that would remove the error.  Same if I run a trunk (3.9)
build of llvm-mc.  Maybe you have ideas on alternative values?

That said, if this instruction form is only available starting with MIPS32r6,
then it needs to be the policy that r6 is the minimum supported CPU for
Chrome/PNaCl - is that the case?

If not, then your ZERO reg solution is probably the way to go.

[Jim Stichnoth, 2016-05-18 18:31:02]

lgtm

[Jim Stichnoth, 2016-05-18 18:31:18]

Description was changed from

==========
Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

This patch adds support for missing integer division instruction sdiv, udiv,
srem, urem.
==========

to

==========
Subzero, MIPS32: Implements integer division instructions sdiv, udiv, srem, urem

This patch adds support for missing integer division instruction sdiv, udiv,
srem, urem.

R=stichnot@chromium.org

Committed:
https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a...
==========

[Jim Stichnoth, 2016-05-18 18:31:20]

Committed patchset #2 (id:20001) manually as
ae93eee8a07d3170fa6c233cbaf3675fe842b034 (presubmit successful).