Re: [PATCH AArch64]Handle REG+REG+CONST and REG+NON_REG+CONST in legitimize address

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 24/11/15 02:51, Bin.Cheng wrote:
>>> The aarch64's problem is we don't define addptr3 pattern, and we don't
>>> >> have direct insn pattern describing the "x + y << z".  According to
>>> >> gcc internal:
>>> >>
>>> >> ‘addptrm3’
>>> >> Like addm3 but is guaranteed to only be used for address calculations.
>>> >> The expanded code is not allowed to clobber the condition code. It
>>> >> only needs to be defined if addm3 sets the condition code.
>> >
>> > addm3 on aarch64 does not set the condition codes, so by this rule we
>> > shouldn't need to define this pattern.
> Hi Richard,
> I think that rule has a prerequisite that backend needs to support
> register shifted addition in addm3 pattern.  

addm3 is a named pattern and its format is well defined.  It does not
take a shifted operand and never has.

> Apparently for AArch64,
> addm3 only supports "reg+reg" or "reg+imm".  Also we don't really
> "does not set the condition codes" actually, because both
> "adds_shift_imm_*" and "adds_mul_imm_*" do set the condition flags.

You appear to be confusing named patterns (used by expand) with
recognizers.  Anyway, we have

(define_insn "*add_<shift>_<mode>"
  [(set (match_operand:GPI 0 "register_operand" "=r")
        (plus:GPI (ASHIFT:GPI (match_operand:GPI 1 "register_operand" "r")
                              (match_operand:QI 2
"aarch64_shift_imm_<mode>" "n"))
                  (match_operand:GPI 3 "register_operand" "r")))]

Which is a non-flag setting add with shifted operand.

> Either way I think it is another backend issue, so do you approve that
> I commit this patch now?

Not yet.  I think there's something fundamental amiss here.

BTW, it looks to me as though addptr<m>3 should have exactly the same
operand rules as add<m>3 (documentation reads "like add<m>3"), so a
shifted operand shouldn't be supported there either.  If that isn't the
case then that should be clearly called out in the documentation.

R.