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.