On 11/12/23 09:52, Richard Sandiford wrote:
SME has various instructions that require aligned register tuples.
However, the associated tuple modes are already widely used and do
not need to be aligned in other contexts. It therefore isn't
appropriate to force alignment in TARGET_HARD_REGNO_MODE_OK.
There are also strided loads and stores that require:
- (regno & 0x8) == 0 for 2-register tuples
- (regno & 0xc) == 0 for 4-register tuples
Although the requirements for strided loads and stores could be
enforced by C++ conditions on the insn, it's convenient to handle
them in the same way as alignment.
This series of patches therefore adds a way for register constraints
to specify which start registers are valid and which aren't. Most of
the details are in the covering note to the first patch.
This is clearly changing a performance-sensitive part of the compiler.
I've tried to ensure that the overhead is only small for targets that
use the new feature. Almost all of the new code gets optimised away
on targets that don't use the feature.
Richard Sandiford (5):
Add register filter operand to define_register_constraint
recog: Handle register filters
lra: Handle register filters
ira: Handle register filters
Add an aligned_register_operand predicate
gcc/common.md | 28 ++++++++
gcc/doc/md.texi | 41 +++++++++++-
gcc/doc/tm.texi | 3 +-
gcc/doc/tm.texi.in | 3 +-
gcc/genconfig.cc | 2 +
gcc/genpreds.cc | 146 ++++++++++++++++++++++++++++++++++++++++-
gcc/gensupport.cc | 48 +++++++++++++-
gcc/gensupport.h | 3 +
gcc/ira-build.cc | 8 +++
gcc/ira-color.cc | 10 +++
gcc/ira-int.h | 14 ++++
gcc/ira-lives.cc | 61 +++++++++++++++++
gcc/lra-constraints.cc | 13 +++-
gcc/recog.cc | 14 +++-
gcc/recog.h | 24 ++++++-
gcc/reginfo.cc | 5 ++
gcc/rtl.def | 6 +-
gcc/target-globals.cc | 6 +-
gcc/target-globals.h | 3 +
19 files changed, 421 insertions(+), 17 deletions(-)
Collecting all occurrence constraints for IRA probably might result in
worse allocation (when pseudo is spilled because of this) in comparison
with using wider hard reg set and generating reload insns for some
pseudo occurrences requiring stricter constraints. Regional RA
mitigates this issue. In any case IRA changes is an improvement in
comparison with using only hard_regno_mode_ok. Using smaller
constraints in certain cases for pseudos spilled after using the biggest
constraint is just an idea for further RA improvement for targets using
the filters. The only question is it worth to implement.
All IRA/LRA/reginfo patches are OK for me. IMHO other changes are
pretty strait forward not to ask somebody to review them.
Thank you, Richard.
