[PATCH] [ARM] Fix required ISA for multiplication instructions

[zhaoshiz at codeaurora.org]

Hi,

r199026 adds alias of MUL/SMLAL/UMLAL for ARMv4.

r199211 removes UMAALv5 since UMAAL is only available for v6 and above.

My patch adds alias of MLA for v4 and changes MLA definitions to use
register class GPRnopc rather than GPR.

Thanks,
Zhaoshi

> There is a bug for this issue: http://llvm.org/bugs/show_bug.cgi?id=17647
> And a patch fix it:
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140113/201434.html
>
> I thought the patch had been committed, but it looks like it was
> approved but not committed.
>
> The reason for the two definitions of the SMLAL instructions is because
> the instruction has some unpredictable behavior on pre-armv6 when the
> destination register is also an output register. The armv6 version is
> less constrained. The constraints need to be respected for instruction
> selection, so the fix was to add an alias that can be used for parsing.
>
> I think the above patch should fix your issue.
>
> On 1/16/2014 7:12 AM, Richard Barton wrote:
>> Hi all
>>
>> You are correct that ARM S/UMLAL are available from ARMv4. UMAAL is only
>> available in ARMv6 and later though, so you need to modify your patch
>> slightly.
>>
>> I’m afraid I am clueless on the instruction selection patches, so I will
>> defer to Renato or Tim for those.
>>
>> Thanks
>>
>> Rich
>>
>> *From:*Renato Golin [mailto:renato.golin at linaro.org]
>> *Sent:* 12 January 2014 14:20
>> *To:* LLVM Commits; Tim Northover; Richard Barton
>> *Subject:* Re: [PATCH] [ARM] Fix required ISA for multiplication
>> instructions
>>
>> Hi Joerg,
>>
>>  From all I know about the early clobber flag in the table gen, your
>> second patch looks fine.
>>
>> Your first patch also looks fine, though SMLALxy is not supported in
>> ARMv4, so you should move its tests to something v5 and
>> use Subtarget.hasV5TEOps().
>>
>> Before committing, I'd welcome reviews from Tim and Richard, just to
>> make sure I'm not missing anything.
>>
>> cheers,
>>
>> --renato
>>
>> On 12 January 2014 03:41, Joerg Sonnenberger <joerg at britannica.bec.de
>> <mailto:joerg at britannica.bec.de>> wrote:
>>
>> On Sun, Jan 12, 2014 at 03:00:51AM +0100, Joerg Sonnenberger wrote:
>>  > while looking at building NetBSD for older ARM ISAs, I hit the issue
>>  > that MC belives that umlal and friends are v6+ only. There seems to
>> be
>>  > no reason for the complications in the matching, so just drop it.
>>
>> Further analysis shows that this is likely a bug in the patterns.
>> Can someone with more ARM knowledge please verify the attached patch?
>>
>> Joerg
>>
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