James Greenhalgh wrote:
> +/* Determine whether a frame chain needs to be generated. */
> +static bool
> +aarch64_needs_frame_chain (void)
> +{
> + /* Force a frame chain for EH returns so the return address is at FP+8. */
> + if (frame_pointer_needed || crtl->calls_eh_return)
> + return true;
> To match the original logic, I think this needs to not return true, but set
> some temporary to true which may be overwritten by...
It's only overwritten if false, once true it cannot ever become false.
> +
> + /* A leaf function cannot have calls or write LR. */
> + bool is_leaf = crtl->is_leaf && !df_regs_ever_live_p (LR_REGNUM);
> +
> + /* Don't use a frame chain in leaf functions if leaf frame pointers
> + are disabled. */
> + if (flag_omit_leaf_frame_pointer && is_leaf)
> + return false;
> This.
No, a leaf function with alloca or EH return still must use a frame pointer.
> +
> + return aarch64_use_frame_pointer;
> +}
> +
> I say that because here
> - /* Force a frame chain for EH returns so the return address is at FP+8. */
> - cfun->machine->frame.emit_frame_chain
> - = frame_pointer_needed || crtl->calls_eh_return;
> -
> We fall through to the next check.
> - /* Emit a frame chain if the frame pointer is enabled.
> - If -momit-leaf-frame-pointer is used, do not use a frame chain
> - in leaf functions which do not use LR. */
> - if (flag_omit_frame_pointer == 2
> - && !(flag_omit_leaf_frame_pointer && crtl->is_leaf
> - && !df_regs_ever_live_p (LR_REGNUM)))
> - cfun->machine->frame.emit_frame_chain = true;
> + cfun->machine->frame.emit_frame_chain = aarch64_needs_frame_chain ();
> That may well have been a long-standing bug, but I wanted to query it
> as you don't mention any bug fixes in the patch cover letter.
There is no bug here, the code is non-trivial but it does exactly what it says -
forcing the frame chain on when required in a non-leaf or a leaf if leaf frame
pointer
omission is disabled. The point of the new code is to make it a bit simpler to
read.
Wilco
