Re: [PATCH][AArch64][v2] Improve comparison with complex immediates followed by branch/cset

[Kyrill Tkachov <kyrylo.tkachov@arm.com>]

Ping.
https://gcc.gnu.org/ml/gcc-patches/2015-11/msg00233.html

Thanks,
Kyrill
On 03/11/15 15:43, Kyrill Tkachov wrote:
> Hi all,
>
> This patch slightly improves sequences where we want to compare against a complex immediate and branch against the result
> or perform a cset on it.
> This means transforming sequences of mov+movk+cmp+branch into sub+subs+branch.
> Similar for cset. Unfortunately I can't just do this by simply matching a (compare (reg) (const_int)) rtx because
> this transformation is only valid for equal/not equal comparisons, not greater than/less than ones but the compare instruction
> pattern only has the general CC mode. We need to also match the use of the condition code.
>
> I've done this by creating a splitter for the conditional jump where the condition is the comparison between the register
> and the complex immediate and splitting it into the sub+subs+condjump sequence. Similar for the cstore pattern.
> Thankfully we don't split immediate moves until later in the optimization pipeline so combine can still try the right patterns.
> With this patch for the example code:
> void g(void);
> void f8(int x)
> {
>    if (x != 0x123456) g();
> }
>
> I get:
> f8:
>         sub     w0, w0, #1191936
>         subs    w0, w0, #1110
>         beq     .L1
>         b       g
>         .p2align 3
> .L1:
>         ret
>
> instead of the previous:
> f8:
>         mov     w1, 13398
>         movk    w1, 0x12, lsl 16
>         cmp     w0, w1
>         beq     .L1
>         b       g
>         .p2align 3
> .L1:
>         ret
>
>
> The condjump case triggered 130 times across all of SPEC2006 which is, admittedly, not much
> whereas the cstore case didn't trigger at all. However, the included testcase in the patch
> demonstrates the kind of code that it would trigger on.
>
> Bootstrapped and tested on aarch64.
>
> Ok for trunk?
>
> Thanks,
> Kyrill
>
>
> 2015-11-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>     * config/aarch64/aarch64.md (*condjump): Rename to...
>     (condjump): ... This.
>     (*compare_condjump<mode>): New define_insn_and_split.
>     (*compare_cstore<mode>_insn): Likewise.
>     (*cstore<mode>_insn): Rename to...
>     (aarch64_cstore<mode>): ... This.
>     * config/aarch64/iterators.md (CMP): Handle ne code.
>     * config/aarch64/predicates.md (aarch64_imm24): New predicate.
>
> 2015-11-03  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>
>     * gcc.target/aarch64/cmpimm_branch_1.c: New test.
>     * gcc.target/aarch64/cmpimm_cset_1.c: Likewise.