llvm dev - May 2015 - [LLVMdev] [ARM backend] adding pattern for SMLALBB

Hi James/Tim,
I am trying to add a patterns for SMLALBB

I think these two assembly patterns can be reduced to SMLALBB using tablegen.

1) 
smulbb  r2, r3, r2
adds    r0, r2, r0 (RdLo)
asr     r3, r2, #31
adc     r1, r3, r1 (RdHi)   ==> smlalbb r0, r1, r3, r2 

I have added pattern in def SMLALBB : AMulxyI64< .....                  as
below :-
[] modified to ---> [((set GPR:$RdLo, (ARMaddc (set GPR:$Rd, mul GPR:$Rn,
GPR:$Rm), GPR:$RdLo)), (set GPR:$RdHi, (ARMadde (sra GPR:$Rd, (i32 31)),
GPR:$RdHi,  CPSR)))]
This results in 'expected identifier in dag init' error.

Obviously something is wrong in this pattern, I have not figured out what that
is ?


2)
ldrb r2, [r2]
ldrb r3, [r3]
smlal r0, r1, r3, r2     ==> smlalbb r0, r1, r3, r2 
def : ARMV5MOPat<(smlal GPRnopc:$RdLo, GPRnopc:$RdHi,
                        (sra (shl GPR:$a, (i32 24)), (i32 24)),
                           (sra (shl GPR:$b, (i32 24)), (i32 24))),
                 (SMLALBB GPRnopc:$RdLo, GPRnopc:$RdHi, GPRnopc:$Rn,
GPRnopc:Rm)>;

This throws "Variable not defined: 'smlal' 

Any pointers on these would be helpful.

Regards,
Jyoti Allur

Hi Jyoti,
> Obviously something is wrong in this pattern, I have not figured out what
that is ?
The biggest problem is you're trying to define two separate values
(RdLo and RdHi). I don't think TableGen supports that yet (I thought
someone had done something recently, but can't find any trace of it).

If so, you'll need to use C++ to match those patterns.
> def : ARMV5MOPat<(smlal GPRnopc:$RdLo, GPRnopc:$RdHi,
>                         (sra (shl GPR:$a, (i32 24)), (i32 24)),
>                            (sra (shl GPR:$b, (i32 24)), (i32 24))),
>                  (SMLALBB GPRnopc:$RdLo, GPRnopc:$RdHi, GPRnopc:$Rn,
GPRnopc:Rm)>;
>
> This throws "Variable not defined: 'smlal'
There is no smlal TableGen node, there's an SMLAL instruction, but you
can't use that as part of an input pattern because selection occurs
only once and bottom-up. Again, I think C++ is your only option here
(the 64-bit values are just not legal enough to effectively use
TableGen on).

Cheers.

Tim.