AArch64Address.lea missed BASE_REGISTER_ONLY case

[Dmitry Samersoff]

Hi Andrew,

Thank you for a detailed explanation. I understand the rationally behind
this error, but couldn't say that API is consistent.

Four constructions below do essentially the same but (a) and (b) works,
when (c) and (d) cause an assert.

It might be better to handle BASE_REGISTER_ONLY the same way as
IMMEDIATE_UNSCALED i.e.:

 case BASE_REGISTER_ONLY:
   if (base.equals(r)) { // it's a nop
      break;
   }

   masm.mov(64, r, base);
   break;


a)
masm.lea(reg,
      AArch64Address.createUnscaledImmediateAddress(array1, 0));

b)
masm.mov(64, tmp, zr);
masm.lea(reg,
    AArch64Address.createRegisterOffsetAddress(array1, tmp, false));

c)
masm.lea(reg,
    AArch64Address.createRegisterOffsetAddress(array1, zr, false));
d)
masm.lea(reg,
     AArch64Address.createBaseRegisterOnlyAddress(array1));

-Dmitry

On 02/28/2018 01:21 PM, Andrew Dinn wrote:
> Hi Dimitry,
> 
> On 27/02/18 18:45, Dmitry Samersoff wrote:
>> Is it a bug? If yes, I'll create a pull requires with the fix.
> Sorry, but no. lea means load effective address. It is there to compute
> an address from a base address provided in some given register combined
> with an offset. The latter is provided either via another register or as
> a constant which can be encoded as an immediate. Essentially, it does an
> add.
> 
> If you just have a base register with no offset to add then lea would
> simply reduce to a register copy. In which case . . . this is not the
> instruction you were looking for. Throwing a Graal shouldNotReachHere
> error is the correct response.
> 
> At present the only place where AArch64ddress.lea gets called in from
> MacroAssembler.lea and that only ever gets called from
> AArch64ArrayEqualsOp with either a register offset address or an
> unscaled immediate address. So, all is well.
> 
> regards,
> 
> 
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
> Registered in England and Wales under Company Registration No. 03798903
> Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander
> 


-- 
Dmitry Samersoff
http://devnull.samersoff.net
* There will come soft rains ...