Re: [PATCH v1] LoongArch: Use current_stack_pointer in current_pt_regs()

[Tiezhu Yang]

On 2026/8/13 下午5:32, Huacai Chen wrote:
> Hi, Tiezhu,
>
> On Thu, Aug 13, 2026 at 5:05 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > The current implementation of current_pt_regs() relies on the compiler
> > __builtin_frame_address(0). This introduces an unnecessary dependency
> > on the frame pointer register, which forces the compiler to generate
> > redundant prologue and epilogue code, create a larger stack frame, and
> > perform redundant memory operations to preserve the frame pointer even
> > in functions where it is otherwise unnecessary.
> >
> > Optimize this by switching to current_stack_pointer, which explicitly
> > maps to the hardware stack pointer register. This allows the compiler
> > to compute the stack alignment directly from the natively maintained
> > $sp register, completely eliminating the overhead of preserving and
> > restoring the frame pointer on the stack memory.
> >
> > As a prominent example, this optimization significantly improves the
> > hot-path function copy_thread(). A localized disassembly comparison
> > of copy_thread() illustrates the elimination of the frame pointer,
> > the reduction of stack frame size from 48 bytes down to 32 bytes,
> > and a more compact epilogue path:
> 3 instructions and 16 bytes stack space. There is improvement, but not
> "significantly".

I used "significantly" from the perspective of hot-path sensitivity,
but I agree that 3 instructions and 16 bytes might be inaccurate.

If the code itself looks good to you, please feel free to update the
commit message as you see fit when applying.

Alternatively, let me know if you prefer me to send a v2 with a more
accurate description.

Thanks,
Tiezhu