Re: [PATCH] Add a target hook for sibcall epilogues

[Jeff Law <jeffreyalaw@gmail.com>]

On 11/11/22 09:22, Richard Sandiford via Gcc-patches wrote:
> Epilogues for sibling calls are generated using the
> sibcall_epilogue pattern.  One disadvantage of this approach
> is that the target doesn't know which call the epilogue is for,
> even though the code that generates the pattern has the call
> to hand.
>
> Although call instructions are currently rtxes, and so could be
> passed as an operand to the pattern, the main point of introducing
> rtx_insn was to move towards separating the rtx and insn types
> (a good thing IMO).  There also isn't an existing practice of
> passing genuine instructions (as opposed to labels) to
> instruction patterns.
>
> This patch therefore adds a hook that can be defined as an
> alternative to sibcall_epilogue.  The advantage is that it
> can be passed the call; the disadvantage is that it can't
> use .md conveniences like generating instructions from
> textual patterns (although most epilogues are too complex
> to benefit much from that anyway).
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?
>
> Richard
>
>
> gcc/
> 	* doc/gccint/target-macros/miscellaneous-parameters.rst:
> 	Add TARGET_EMIT_EPILOGUE_FOR_SIBCALL.
> 	* doc/gccint/target-macros/tm.rst.in: Regenerate.
> 	* target.def (emit_epilogue_for_sibcall): New hook.
> 	* calls.cc (can_implement_as_sibling_call_p): Use it.
> 	* function.cc (thread_prologue_and_epilogue_insns): Likewise.
> 	(reposition_prologue_and_epilogue_notes): Likewise.
> 	* config/aarch64/aarch64-protos.h (aarch64_expand_epilogue): Take
> 	an rtx_call_insn * rather than a bool.
> 	* config/aarch64/aarch64.cc (aarch64_expand_epilogue): Likewise.
> 	(TARGET_EMIT_EPILOGUE_FOR_SIBCALL): Define.
> 	* config/aarch64/aarch64.md (epilogue): Update call.
> 	(sibcall_epilogue): Delete.

Presumably you're going to do something useful with the new hook :-)


OK.

jeff