From: "H.J. Lu" <hjl.tools@gmail.com>
To: gcc-patches@gcc.gnu.org
Cc: ubizjak@gmail.com, hongtao.liu@intel.com, jh@suse.cz
Subject: [PATCH v3 0/2] x86: Don't save callee-saved registers if not needed
Date: Tue, 23 Jan 2024 06:59:49 -0800 [thread overview]
Message-ID: <20240123145951.2092315-1-hjl.tools@gmail.com> (raw)
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.
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
next reply other threads:[~2024-01-23 14:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-23 14:59 H.J. Lu [this message]
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 ` [PATCH v3 0/2] x86: Don't save callee-saved registers if not needed Hongtao Liu
2024-01-27 11:17 ` H.J. Lu
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