From: Hongtao Liu <crazylht@gmail.com>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: gcc-patches@gcc.gnu.org, ubizjak@gmail.com,
hongtao.liu@intel.com, jh@suse.cz
Subject: Re: [PATCH v3 0/2] x86: Don't save callee-saved registers if not needed
Date: Thu, 25 Jan 2024 11:36:03 +0800 [thread overview]
Message-ID: <CAMZc-bw++EkWtcpMjuMrrNrnZ=E4TzJa3uMCzKWzELURgDNzcA@mail.gmail.com> (raw)
In-Reply-To: <20240123145951.2092315-1-hjl.tools@gmail.com>
On Tue, Jan 23, 2024 at 11:00 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Changes in v3:
>
> 1. Rebase against commit 02e68389494
> 2. Don't add call_no_callee_saved_registers to machine_function since
> all callee-saved registers are properly clobbered by callee with
> no_callee_saved_registers attribute.
>
The patch LGTM, it should be low risk since there's already
no_caller_save_registers attribute, the patch just extends to
no_callee_save_registers with the same approach.
So if there's no objection(or any concerns) in the next couple days,
I'm ok for the patch to be in GCC14 and backport.
> Changes in v2:
>
> 1. Rebase against commit f9df00340e3
> 2. Don't add redundant clobbered_registers check in ix86_expand_call.
>
> In some cases, there are no need to save callee-saved registers:
>
> 1. If a noreturn function doesn't throw nor support exceptions, it can
> skip saving callee-saved registers.
>
> 2. 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.
>
> This patch set adds no_callee_saved_registers function attribute, which
> is complementary to no_caller_saved_registers function attribute, to
> classify x86 backend 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.
>
> Functions of no callee-saved registers won't save callee-saved registers.
> If a noreturn function doesn't throw nor support exceptions, it is
> classified as the no callee-saved registers type.
>
> With these changes, __libc_start_main in glibc 2.39, which is a noreturn
> function, is changed from
>
> __libc_start_main:
> endbr64
> push %r15
> push %r14
> mov %rcx,%r14
> push %r13
> push %r12
> push %rbp
> mov %esi,%ebp
> push %rbx
> mov %rdx,%rbx
> sub $0x28,%rsp
> mov %rdi,(%rsp)
> mov %fs:0x28,%rax
> mov %rax,0x18(%rsp)
> xor %eax,%eax
> test %r9,%r9
>
> to
>
> __libc_start_main:
> endbr64
> sub $0x28,%rsp
> mov %esi,%ebp
> mov %rdx,%rbx
> mov %rcx,%r14
> mov %rdi,(%rsp)
> mov %fs:0x28,%rax
> mov %rax,0x18(%rsp)
> xor %eax,%eax
> test %r9,%r9
>
> In Linux kernel 6.7.0 on x86-64, do_exit is changed from
>
> do_exit:
> endbr64
> call <do_exit+0x9>
> push %r15
> push %r14
> push %r13
> push %r12
> mov %rdi,%r12
> push %rbp
> push %rbx
> mov %gs:0x0,%rbx
> sub $0x28,%rsp
> mov %gs:0x28,%rax
> mov %rax,0x20(%rsp)
> xor %eax,%eax
> call *0x0(%rip) # <do_exit+0x39>
> test $0x2,%ah
> je <do_exit+0x8d3>
>
> to
>
> do_exit:
> endbr64
> call <do_exit+0x9>
> sub $0x28,%rsp
> mov %rdi,%r12
> mov %gs:0x28,%rax
> mov %rax,0x20(%rsp)
> xor %eax,%eax
> mov %gs:0x0,%rbx
> call *0x0(%rip) # <do_exit+0x2f>
> test $0x2,%ah
> je <do_exit+0x8c9>
>
> I compared GCC master branch bootstrap and test times on a slow machine
> with 6.6 Linux kernels compiled with the original GCC 13 and the GCC 13
> with the backported patch. The performance data isn't precise since the
> measurements were done on different days with different GCC sources under
> different 6.6 kernel versions.
>
> GCC master branch build time in seconds:
>
> before after improvement
> 30043.75user 30013.16user 0%
> 1274.85system 1243.72system 2.4%
>
> GCC master branch test time in seconds (new tests added):
>
> before after improvement
> 216035.90user 216547.51user 0
> 27365.51system 26658.54system 2.6%
>
> Backported to GCC 13 to rebuild system glibc and kernel on Fedora 39.
> Systems perform normally.
>
>
> H.J. Lu (2):
> x86: Add no_callee_saved_registers function attribute
> x86: Don't save callee-saved registers in noreturn functions
>
> gcc/config/i386/i386-expand.cc | 52 +++++++++++++---
> gcc/config/i386/i386-options.cc | 61 +++++++++++++++----
> gcc/config/i386/i386.cc | 57 +++++++++++++----
> gcc/config/i386/i386.h | 16 ++++-
> gcc/doc/extend.texi | 8 +++
> .../gcc.dg/torture/no-callee-saved-run-1a.c | 23 +++++++
> .../gcc.dg/torture/no-callee-saved-run-1b.c | 59 ++++++++++++++++++
> .../gcc.target/i386/no-callee-saved-1.c | 30 +++++++++
> .../gcc.target/i386/no-callee-saved-10.c | 46 ++++++++++++++
> .../gcc.target/i386/no-callee-saved-11.c | 11 ++++
> .../gcc.target/i386/no-callee-saved-12.c | 10 +++
> .../gcc.target/i386/no-callee-saved-13.c | 16 +++++
> .../gcc.target/i386/no-callee-saved-14.c | 16 +++++
> .../gcc.target/i386/no-callee-saved-15.c | 17 ++++++
> .../gcc.target/i386/no-callee-saved-16.c | 16 +++++
> .../gcc.target/i386/no-callee-saved-17.c | 16 +++++
> .../gcc.target/i386/no-callee-saved-18.c | 51 ++++++++++++++++
> .../gcc.target/i386/no-callee-saved-2.c | 30 +++++++++
> .../gcc.target/i386/no-callee-saved-3.c | 8 +++
> .../gcc.target/i386/no-callee-saved-4.c | 8 +++
> .../gcc.target/i386/no-callee-saved-5.c | 11 ++++
> .../gcc.target/i386/no-callee-saved-6.c | 12 ++++
> .../gcc.target/i386/no-callee-saved-7.c | 49 +++++++++++++++
> .../gcc.target/i386/no-callee-saved-8.c | 50 +++++++++++++++
> .../gcc.target/i386/no-callee-saved-9.c | 49 +++++++++++++++
> gcc/testsuite/gcc.target/i386/pr38534-1.c | 26 ++++++++
> gcc/testsuite/gcc.target/i386/pr38534-2.c | 18 ++++++
> gcc/testsuite/gcc.target/i386/pr38534-3.c | 19 ++++++
> gcc/testsuite/gcc.target/i386/pr38534-4.c | 18 ++++++
> .../gcc.target/i386/stack-check-17.c | 19 +++---
> 30 files changed, 775 insertions(+), 47 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/torture/no-callee-saved-run-1a.c
> create mode 100644 gcc/testsuite/gcc.dg/torture/no-callee-saved-run-1b.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-10.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-11.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-12.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-13.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-14.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-15.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-16.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-17.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-18.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-2.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-3.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-4.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-5.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-6.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-7.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-8.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-9.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-1.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-2.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-3.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-4.c
>
> --
> 2.43.0
>
--
BR,
Hongtao
next prev parent reply other threads:[~2024-01-25 3:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-23 14:59 H.J. Lu
2024-01-23 14:59 ` [PATCH v3 1/2] x86: Add no_callee_saved_registers function attribute H.J. Lu
2024-01-23 14:59 ` [PATCH v3 2/2] x86: Don't save callee-saved registers in noreturn functions H.J. Lu
2024-01-25 3:36 ` Hongtao Liu [this message]
2024-01-27 11:17 ` [PATCH v3 0/2] x86: Don't save callee-saved registers if not needed H.J. Lu
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