[Patch]New InstCombine pattern for Icmp

[Nuno Lopes]

Hi Yi,

ALIVe still complains, I'm afraid:

Precondition: isPowerOf2(C1 ^ C2) && ugt(C1, C3) && ugt(C2, C3)
%x = add %A, C1
%i = icmp ult %x, C3
%y = add %A, C2
%j = icmp ult %y, C3
%r = or %i, %j
  =>
%and = and %A, ~(C1 ^ C2)
%lhs = add %and, umax(C1, C2)
%r = icmp ult %lhs, C3

Done: 1
ERROR: Mismatch in values of i1 %r

Example:
%A i2 = 2 (0x2)
C1 i2 = 3 (0x3)
%x i2 = 1 (0x1)
C3 i2 = 1 (0x1)
%i i1 = 0 (0x0)
C2 i2 = 2 (0x2)
%y i2 = 0 (0x0)
%j i1 = 1 (0x1)
%and i2 = 2 (0x2)
%lhs i2 = 1 (0x1)
Source value: 1 (0x1)
Target value: 0 (0x0)


Nuno

----- Original Message ----- 
From: "Yi Jiang" <yjiang at apple.com>
To: "Nuno Lopes" <nuno.lopes at ist.utl.pt>
Cc: "LLVM Commits" <llvm-commits at cs.uiuc.edu>
Sent: Wednesday, July 30, 2014 8:28 PM
Subject: Re: [Patch]New InstCombine pattern for Icmp


Hi Nuno,

Thank you for pointing out this! One condition is missing: C1 and C2 should 
be unsigned greater than C3.
Here is the new patch.

-Yi

On Jul 29, 2014, at 11:34 AM, Nuno Lopes <nuno.lopes at ist.utl.pt> wrote:

> Hi,
>
> I sent you an email the other day, but it was rejected by Apple's email 
> server.  Tyring now through another email account.
> Please take a look here: 
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140721/227575.html
>
> Nuno
>
> ----- Original Message -----
>
> Ping...
> On Jul 25, 2014, at 4:11 PM, Yi Jiang <yjiang at apple.com> wrote:
>
>> Hi Ben,
>>
>> Thank you for your comments! Here is a new version.  In this version, I 
>> still kept some "if" thinking that some operand has been already 
>> extracted so I would like to use it directly.  Please let me know if any 
>> other comments.
>> <combinecmpV2.patch>
>> -Yi
>> On Jul 25, 2014, at 2:12 AM, Benjamin Kramer <benny.kra at gmail.com> wrote:
>>
>>> On Fri, Jul 25, 2014 at 1:24 AM, Yi Jiang <yjiang at apple.com> wrote:
>>>> Hi,
>>>>
>>>> his patch is trying to fold (icmp ult/ule (A + C1), C3) | (icmp ult/ule 
>>>> (A +
>>>> C2), C3)  to (icmp ult/ule ((A & ~(C1 ^ C2)) + max(C1, C2)), C3)  .
>>>> This transformation is legal if C1 ^ C2 is one-bit mask, in other word, 
>>>> C1
>>>> is only one bit different from C2. In this case, we can "mask" that bit 
>>>> and
>>>> do just one comparison.
>>>> A typical example is:
>>>> isALPHA(c)    ((c) >= 'A' && (c) <= 'Z') || ((c) >= 'a' && (c) <= 'z')
>>>>
>>>> Now llvm will optimize it to ((c + 191) <=25) || ((c + 159) <=25)
>>>>
>>>> With this patch, we can optimize it further to:
>>>> (c & 223) + 191 <= 25
>>>>
>>>> The binary format of the constants are:
>>>> 191   10111111
>>>> 159   10011111
>>>> 223   11011111
>>>>
>>>> Here is some experiment result on arm64:
>>>> The patch shows no regression and improve spec2000 perlbmk 3.8% in
>>>> test-suite under -O3.
>>>> We also test the spec2006 400.perlbench with ref size input, it will 
>>>> improve
>>>> 1% under -O3 and 1.2% under -O3+lto+pgo.
>>>
>>> Wow, very nice.
>>>
>>>> Any comments are appreciated.
>>>
>>> The patch could be significantly simplified with the PatternMatch
>>> tool. Something like match(LHS, m_Add(m_OneUse(m_Value(A),
>>> m_ConstantInt(LAddCst)... could replace your if chain.
>>>
>>> - Ben