On Fri, Sep 25, 2026 at 6:37 AM Wilco Dijkstra <[email protected]> wrote:
>
> v2: Rebased, update description
>
> TARGET_CONST_ANCHOR appears to trigger too often, even on simple immediates.
Maybe we should fix how TARGET_CONST_ANCHOR is handled rather than removing it.
I suspect part of the problem with TARGET_CONST_ANCHOR is it was
designed for mips which didn't have the ability to form masks/single
bits using one instruction.
At least it would be useful to add a testcase where it is being hit
for simple immediates. This would also help judge this patch alone if
it is a good idea to remove it for now.
I do think we should at least file a few missed optimization issues
either way we decide on TARGET_CONST_ANCHOR; ones where we missing out
from not removing it or the ones we are now missing out from removing
it.
Thanks,
Andrea
> It inserts extra ADD/SUB instructions even when a single MOV exists.
> Disable it to improve overall code quality: on SPEC2017 it removes 2100+
> ADD/SUB instructions. Adjust a testcase that was confusing neg and fneg.
>
> gcc:
> * config/aarch64/aarch64.cc (TARGET_CONST_ANCHOR): Remove.
>
> gcc/testsuite:
> * gcc.target/aarch64/vneg_s.c: Update test.
>
> ---
>
> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> index
> 107271b040454605fc40abba3fe5d678a8e27104..6d3319f8092b151efc0d41dbce230b40abbd8044
> 100644
> --- a/gcc/config/aarch64/aarch64.cc
> +++ b/gcc/config/aarch64/aarch64.cc
> @@ -34928,9 +34928,6 @@ aarch64_libgcc_floating_mode_supported_p
> #undef TARGET_HAVE_SHADOW_CALL_STACK
> #define TARGET_HAVE_SHADOW_CALL_STACK true
>
> -#undef TARGET_CONST_ANCHOR
> -#define TARGET_CONST_ANCHOR 0x1000000
> -
> #undef TARGET_EXTRA_LIVE_ON_ENTRY
> #define TARGET_EXTRA_LIVE_ON_ENTRY aarch64_extra_live_on_entry
>
> diff --git a/gcc/testsuite/gcc.target/aarch64/vneg_s.c
> b/gcc/testsuite/gcc.target/aarch64/vneg_s.c
> index
> 8ddc4d21c1f89d6c66624a33ee0386cb3a28c512..8d91639faaa1c728095265ce4e61327a4dc441e3
> 100644
> --- a/gcc/testsuite/gcc.target/aarch64/vneg_s.c
> +++ b/gcc/testsuite/gcc.target/aarch64/vneg_s.c
> @@ -256,7 +256,7 @@ test_vnegq_s64 ()
> return o1||o2||o2||o4;
> }
>
> -/* { dg-final { scan-assembler-times "neg\\tv\[0-9\]+\.2d, v\[0-9\]+\.2d" 1
> } } */
> +/* { dg-final { scan-assembler-times "\tneg\\tv\[0-9\]+\.2d, v\[0-9\]+\.2d"
> 1 } } */
>
> int
> main (int argc, char **argv)
>
