On 5/20/25 1:22 AM, Stefan Schulze Frielinghaus wrote:
Implement hard register constraints of the form {regname} where regname
must be a valid register name for the target. Such constraints may be
used in asm statements as a replacement for register asm and in machine
descriptions.
It is expected and desired that optimizations coalesce multiple pseudos
into one whenever possible. However, in case of hard register
constraints we may have to undo this and introduce copies since
otherwise we could constraint a single pseudo to different hard
registers. Therefore, we have to introduce copies of such a pseudo and
use these for conflicting inputs. This is done prior RA during asmcons
in match_asm_constraints_2(). While IRA tries to reduce live ranges, it
also replaces some register-register moves. That in turn might undo
those copies of a pseudo which we just introduced during asmcons. Thus,
check in decrease_live_ranges_number() via
valid_replacement_for_asm_input_p() whether it is valid to perform a
replacement.
The reminder of the patch mostly deals with parsing and decoding hard
register constraints. The actual work is done by LRA in
process_alt_operands() where a register filter, according to the
constraint, is installed.
For the sake of "reviewability" and in order to show the beauty of LRA,
error handling (which gets pretty involved) is spread out into a
subsequent patch.
Limitation
----------
Currently, a fixed register cannot be used as hard register constraint.
For example, loading the stack pointer on x86_64 via
void *
foo (void)
{
void *y;
__asm__ ("" : "={rsp}" (y));
return y;
}
leads to an error. This is unfortunate since register asm does not have
this limitation. The culprit seems to be that during reload
ira_class_hard_regs_num[rclass] does not even include fixed registers
which is why lra_assign() ultimately fails. Does anyone have an idea
how to lift this limitation? Maybe there is even a shortcut in order to
force a pseudo into a hard reg?
Asm Adjust Hook
---------------
The following targets implement TARGET_MD_ASM_ADJUST:
- aarch64
- arm
- avr
- cris
- i386
- mn10300
- nds32
- pdp11
- rs6000
- s390
- vax
Most of them only add the CC register to the list of clobbered register.
However, cris, i386, and s390 need some minor adjustment.
---
gcc/config/cris/cris.cc | 6 +-
gcc/config/i386/i386.cc | 6 +
gcc/config/s390/s390.cc | 6 +-
gcc/doc/extend.texi | 178 ++++++++++++++++++
gcc/doc/md.texi | 6 +
gcc/function.cc | 116 ++++++++++++
gcc/genoutput.cc | 14 ++
gcc/genpreds.cc | 4 +-
gcc/ira.cc | 79 +++++++-
gcc/lra-constraints.cc | 13 ++
gcc/recog.cc | 11 +-
gcc/stmt.cc | 39 ++++
gcc/stmt.h | 1 +
gcc/testsuite/gcc.dg/asm-hard-reg-1.c | 85 +++++++++
gcc/testsuite/gcc.dg/asm-hard-reg-2.c | 33 ++++
gcc/testsuite/gcc.dg/asm-hard-reg-3.c | 25 +++
gcc/testsuite/gcc.dg/asm-hard-reg-4.c | 50 +++++
gcc/testsuite/gcc.dg/asm-hard-reg-5.c | 36 ++++
gcc/testsuite/gcc.dg/asm-hard-reg-6.c | 60 ++++++
gcc/testsuite/gcc.dg/asm-hard-reg-7.c | 41 ++++
gcc/testsuite/gcc.dg/asm-hard-reg-8.c | 49 +++++
.../gcc.target/aarch64/asm-hard-reg-1.c | 55 ++++++
.../gcc.target/i386/asm-hard-reg-1.c | 115 +++++++++++
.../gcc.target/s390/asm-hard-reg-1.c | 103 ++++++++++
.../gcc.target/s390/asm-hard-reg-2.c | 43 +++++
.../gcc.target/s390/asm-hard-reg-3.c | 42 +++++
.../gcc.target/s390/asm-hard-reg-4.c | 6 +
.../gcc.target/s390/asm-hard-reg-5.c | 6 +
.../gcc.target/s390/asm-hard-reg-6.c | 152 +++++++++++++++
.../gcc.target/s390/asm-hard-reg-longdouble.h | 18 ++
30 files changed, 1391 insertions(+), 7 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-1.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-2.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-3.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-4.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-5.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-6.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-7.c
create mode 100644 gcc/testsuite/gcc.dg/asm-hard-reg-8.c
create mode 100644 gcc/testsuite/gcc.target/aarch64/asm-hard-reg-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/asm-hard-reg-1.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-1.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-2.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-3.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-4.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-5.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-6.c
create mode 100644 gcc/testsuite/gcc.target/s390/asm-hard-reg-longdouble.h
So you need a ChangeLog, but this is OK once the ChangeLog is cobbled
together. I think you should wait to commit until all 4 patches in this
series are ACK'd though.
jeff
