[PATCH] AArch64: Implement common instruction aliases

[James Molloy]

Hi Tim,

 

The attached patches provide instruction aliases for negated or complemented
immediates. The logicalimm patch implements:

 

BIC Rd, Rn, #imm -> AND Rd, Rn, #~imm

And similarly for ORN, EON and BICS.

 

The addsubimm patch implements:

 

ADD Rd, Rn, #imm (imm < 0) -> SUB Rd, Rn, #-imm

And similarly for SUB, ADDS, SUBS and CMP.

 

This is my first patch to the MC layer in quite a while so please don't
assume I have any competence in this area when reviewing J

 

In particular, I don't know quite what to do about:

 

    def _posimm_neg_lsl12 : Operand<ty>,

        ImmLeaf<ty, [{ return Imm >= 0 && (Imm & ~0xfff000) == 0; }],

                shr_12_XFORM>;

 

The ImmLeaf was basically copied from the non-negated operand variant, but
as this operand type is never going to be used for instruction selection
(It's for passing to an InstAlias only), I'm not sure if (a) I need an
ImmLeaf or PatLeaf at all or (b) if I do,if the predicate should just
"return false;". Advice here would be really useful.

 

Cheers,

 

James
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