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* [Bug target/103503] New: RFE: no save registers attribute
@ 2021-11-30 18:06 hpa at zytor dot com
2021-11-30 21:00 ` [Bug target/103503] " pinskia at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: hpa at zytor dot com @ 2021-11-30 18:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
Bug ID: 103503
Summary: RFE: no save registers attribute
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: hpa at zytor dot com
Target Milestone: ---
Target: multiple
When a common assembly interrupt entry code or an equivalent hardware engine is
used to handle register saves in an interrupt routine, it may be completely
unnecessary to save and restore registers in the interrupt handler itself, even
if they would normally be clobbered.
Unfortunately [-f]call-used-reg is not supported by either
__attribute__((optimize)) nor _Pragma("GCC optimize"); otherwise that would be
a very valid solution.
Putting all interrupt handlers in a separate compilation unit is awkward at the
very best.
AVR has __attribute__((OS_{task,main})) for this purpose, but being able to do
it in general would improve interrupt/trap latency.
See also bug 38534.
Note: not saving the registers in the assembly wrapper is generally not an
option; similarly, whether or not a hardware engine can do it practically
depends on both the hardware implementation and the ABI. The RISC-V ABI, for
example, scatters clobbered and saved registers all over the register map,
which makes doing such a thing in hardware difficult.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
@ 2021-11-30 21:00 ` pinskia at gcc dot gnu.org
2021-11-30 21:02 ` pinskia at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-30 21:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
x86 (and I think MIPS) has an interrupt attribute, will that work instead?
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
2021-11-30 21:00 ` [Bug target/103503] " pinskia at gcc dot gnu.org
@ 2021-11-30 21:02 ` pinskia at gcc dot gnu.org
2021-11-30 21:03 ` pinskia at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-30 21:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
RISCV does have the interrupt attribute too which should work here.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
2021-11-30 21:00 ` [Bug target/103503] " pinskia at gcc dot gnu.org
2021-11-30 21:02 ` pinskia at gcc dot gnu.org
@ 2021-11-30 21:03 ` pinskia at gcc dot gnu.org
2021-11-30 21:03 ` pinskia at gcc dot gnu.org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-30 21:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
the only major target which does not have the interrupt attribute is aarch64.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
` (2 preceding siblings ...)
2021-11-30 21:03 ` pinskia at gcc dot gnu.org
@ 2021-11-30 21:03 ` pinskia at gcc dot gnu.org
2022-06-06 17:00 ` hpa at zytor dot com
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-11-30 21:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
` (3 preceding siblings ...)
2021-11-30 21:03 ` pinskia at gcc dot gnu.org
@ 2022-06-06 17:00 ` hpa at zytor dot com
2024-01-11 3:44 ` hjl.tools at gmail dot com
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: hpa at zytor dot com @ 2022-06-06 17:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #4 from H. Peter Anvin <hpa at zytor dot com> ---
The interrupt attribute typically does two things:
1. It changes the return instruction;
2. It marks all registers as saved.
2 is exactly the *opposite* of what I want; I would like to improve performance
by the fact that the compiler-invisible entry flow has already saved all
registers, whether or not they are saved in the ABI. Thus, I would like it to
treat all (non-fixed) registers as *clobbered*, not *saved*.
Ideally, "nosaved" and "interrupt" should be possible to use together, to get
effect #1 of the interrupt attribute, but that is usually less important.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
` (4 preceding siblings ...)
2022-06-06 17:00 ` hpa at zytor dot com
@ 2024-01-11 3:44 ` hjl.tools at gmail dot com
2024-01-27 12:19 ` cvs-commit at gcc dot gnu.org
2024-05-15 16:17 ` hpa at zytor dot com
7 siblings, 0 replies; 9+ messages in thread
From: hjl.tools at gmail dot com @ 2024-01-11 3:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2024-01-11
--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
There is no_caller_saved_registers attribute. We can add
no_callee_saved_registers attribute.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
` (5 preceding siblings ...)
2024-01-11 3:44 ` hjl.tools at gmail dot com
@ 2024-01-27 12:19 ` cvs-commit at gcc dot gnu.org
2024-05-15 16:17 ` hpa at zytor dot com
7 siblings, 0 replies; 9+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-01-27 12:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:
https://gcc.gnu.org/g:a96549dce7636edfc693bf758ef27fcd8adc6161
commit r14-8469-ga96549dce7636edfc693bf758ef27fcd8adc6161
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Tue Jan 23 06:59:50 2024 -0800
x86: Add no_callee_saved_registers function attribute
When an interrupt handler is implemented by an assembly stub which does:
1. Save all registers.
2. Call a C function.
3. Restore all registers.
4. Return from interrupt.
it is completely unnecessary to save and restore any registers in the C
function called by the assembly stub, even if they would normally be
callee-saved.
Add no_callee_saved_registers function attribute, which is complementary
to no_caller_saved_registers function attribute, to mark a function which
doesn't have any callee-saved registers. Such a function won't save and
restore any registers. Classify function call-saved register handling
type with:
1. Default call-saved registers.
2. No caller-saved registers with no_caller_saved_registers attribute.
3. No callee-saved registers with no_callee_saved_registers attribute.
Disallow sibcall if callee is a no_callee_saved_registers function
and caller isn't a no_callee_saved_registers function. Otherwise,
callee-saved registers won't be preserved.
After a no_callee_saved_registers function is called, all registers may
be clobbered. If the calling function isn't a no_callee_saved_registers
function, we need to preserve all registers which aren't used by function
calls.
gcc/
PR target/103503
PR target/113312
* config/i386/i386-expand.cc (ix86_expand_call): Replace
no_caller_saved_registers check with call_saved_registers check.
Clobber all registers that are not used by the callee with
no_callee_saved_registers attribute.
* config/i386/i386-options.cc (ix86_set_func_type): Set
call_saved_registers to TYPE_NO_CALLEE_SAVED_REGISTERS for
noreturn function. Disallow no_callee_saved_registers with
interrupt or no_caller_saved_registers attributes together.
(ix86_set_current_function): Replace no_caller_saved_registers
check with call_saved_registers check.
(ix86_handle_no_caller_saved_registers_attribute): Renamed to ...
(ix86_handle_call_saved_registers_attribute): This.
(ix86_gnu_attributes): Add
ix86_handle_call_saved_registers_attribute.
* config/i386/i386.cc (ix86_conditional_register_usage): Replace
no_caller_saved_registers check with call_saved_registers check.
(ix86_function_ok_for_sibcall): Don't allow callee with
no_callee_saved_registers attribute when the calling function
has callee-saved registers.
(ix86_comp_type_attributes): Also check
no_callee_saved_registers.
(ix86_epilogue_uses): Replace no_caller_saved_registers check
with call_saved_registers check.
(ix86_hard_regno_scratch_ok): Likewise.
(ix86_save_reg): Replace no_caller_saved_registers check with
call_saved_registers check. Don't save any registers for
TYPE_NO_CALLEE_SAVED_REGISTERS. Save all registers with
TYPE_DEFAULT_CALL_SAVED_REGISTERS if function with
no_callee_saved_registers attribute is called.
(find_drap_reg): Replace no_caller_saved_registers check with
call_saved_registers check.
* config/i386/i386.h (call_saved_registers_type): New enum.
(machine_function): Replace no_caller_saved_registers with
call_saved_registers.
* doc/extend.texi: Document no_callee_saved_registers attribute.
gcc/testsuite/
PR target/103503
PR target/113312
* gcc.dg/torture/no-callee-saved-run-1a.c: New file.
* gcc.dg/torture/no-callee-saved-run-1b.c: Likewise.
* gcc.target/i386/no-callee-saved-1.c: Likewise.
* gcc.target/i386/no-callee-saved-2.c: Likewise.
* gcc.target/i386/no-callee-saved-3.c: Likewise.
* gcc.target/i386/no-callee-saved-4.c: Likewise.
* gcc.target/i386/no-callee-saved-5.c: Likewise.
* gcc.target/i386/no-callee-saved-6.c: Likewise.
* gcc.target/i386/no-callee-saved-7.c: Likewise.
* gcc.target/i386/no-callee-saved-8.c: Likewise.
* gcc.target/i386/no-callee-saved-9.c: Likewise.
* gcc.target/i386/no-callee-saved-10.c: Likewise.
* gcc.target/i386/no-callee-saved-11.c: Likewise.
* gcc.target/i386/no-callee-saved-12.c: Likewise.
* gcc.target/i386/no-callee-saved-13.c: Likewise.
* gcc.target/i386/no-callee-saved-14.c: Likewise.
* gcc.target/i386/no-callee-saved-15.c: Likewise.
* gcc.target/i386/no-callee-saved-16.c: Likewise.
* gcc.target/i386/no-callee-saved-17.c: Likewise.
* gcc.target/i386/no-callee-saved-18.c: Likewise.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/103503] RFE: no save registers attribute
2021-11-30 18:06 [Bug target/103503] New: RFE: no save registers attribute hpa at zytor dot com
` (6 preceding siblings ...)
2024-01-27 12:19 ` cvs-commit at gcc dot gnu.org
@ 2024-05-15 16:17 ` hpa at zytor dot com
7 siblings, 0 replies; 9+ messages in thread
From: hpa at zytor dot com @ 2024-05-15 16:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103503
--- Comment #7 from H. Peter Anvin <hpa at zytor dot com> ---
Note: this is now implemented for x86, but it affects other targets as well.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2021-11-30 21:02 ` pinskia at gcc dot gnu.org
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