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 | 58 +++++++++++++-- gcc/config/i386/i386-options.cc | 61 ++++++++++++---- gcc/config/i386/i386.cc | 70 +++++++++++++++---- gcc/config/i386/i386.h | 20 +++++- 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, 797 insertions(+), 48 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