[PATCH] Add a target hook for sibcall epilogues

[PATCH] Add a target hook for sibcall epilogues

[Richard Sandiford]

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.
---
 gcc/calls.cc                                      |  3 ++-
 gcc/config/aarch64/aarch64-protos.h               |  2 +-
 gcc/config/aarch64/aarch64.cc                     | 11 +++++++----
 gcc/config/aarch64/aarch64.md                     | 11 +----------
 .../target-macros/miscellaneous-parameters.rst    |  5 +++++
 gcc/doc/gccint/target-macros/tm.rst.in            | 11 +++++++++++
 gcc/function.cc                                   | 15 +++++++++++++--
 gcc/target.def                                    |  9 +++++++++
 8 files changed, 49 insertions(+), 18 deletions(-)

diff --git a/gcc/calls.cc b/gcc/calls.cc
index 6dd6f73e978..51b664f1b4d 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -2493,7 +2493,8 @@ can_implement_as_sibling_call_p (tree exp,
 				 tree addr,
 				 const args_size &args_size)
 {
-  if (!targetm.have_sibcall_epilogue ())
+  if (!targetm.have_sibcall_epilogue ()
+      && !targetm.emit_epilogue_for_sibcall)
     {
       maybe_complain_about_tail_call
 	(exp,
diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index 238820581c5..3d81c223b01 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -886,7 +886,7 @@ const char * aarch64_gen_far_branch (rtx *, int, const char *, const char *);
 const char * aarch64_output_probe_stack_range (rtx, rtx);
 const char * aarch64_output_probe_sve_stack_clash (rtx, rtx, rtx, rtx);
 void aarch64_err_no_fpadvsimd (machine_mode);
-void aarch64_expand_epilogue (bool);
+void aarch64_expand_epilogue (rtx_call_insn *);
 rtx aarch64_ptrue_all (unsigned int);
 opt_machine_mode aarch64_ptrue_all_mode (rtx);
 rtx aarch64_convert_sve_data_to_pred (rtx, machine_mode, rtx);
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index d1f979ebcf8..41a2181a7d3 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -10003,7 +10003,7 @@ aarch64_use_return_insn_p (void)
    from a deallocated stack, and we optimize the unwind records by
    emitting them all together if possible.  */
 void
-aarch64_expand_epilogue (bool for_sibcall)
+aarch64_expand_epilogue (rtx_call_insn *sibcall)
 {
   poly_int64 initial_adjust = cfun->machine->frame.initial_adjust;
   HOST_WIDE_INT callee_adjust = cfun->machine->frame.callee_adjust;
@@ -10151,7 +10151,7 @@ aarch64_expand_epilogue (bool for_sibcall)
 	   explicitly authenticate.
     */
   if (aarch64_return_address_signing_enabled ()
-      && (for_sibcall || !TARGET_ARMV8_3))
+      && (sibcall || !TARGET_ARMV8_3))
     {
       switch (aarch64_ra_sign_key)
 	{
@@ -10169,7 +10169,7 @@ aarch64_expand_epilogue (bool for_sibcall)
     }
 
   /* Stack adjustment for exception handler.  */
-  if (crtl->calls_eh_return && !for_sibcall)
+  if (crtl->calls_eh_return && !sibcall)
     {
       /* We need to unwind the stack by the offset computed by
 	 EH_RETURN_STACKADJ_RTX.  We have already reset the CFA
@@ -10180,7 +10180,7 @@ aarch64_expand_epilogue (bool for_sibcall)
     }
 
   emit_use (gen_rtx_REG (DImode, LR_REGNUM));
-  if (!for_sibcall)
+  if (!sibcall)
     emit_jump_insn (ret_rtx);
 }
 
@@ -27906,6 +27906,9 @@ aarch64_libgcc_floating_mode_supported_p
 #undef TARGET_HAVE_SHADOW_CALL_STACK
 #define TARGET_HAVE_SHADOW_CALL_STACK true
 
+#undef TARGET_EMIT_EPILOGUE_FOR_SIBCALL
+#define TARGET_EMIT_EPILOGUE_FOR_SIBCALL aarch64_expand_epilogue
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-aarch64.h"
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index f2e3d905dbb..c4581cb823f 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -868,16 +868,7 @@ (define_expand "epilogue"
   [(clobber (const_int 0))]
   ""
   "
-  aarch64_expand_epilogue (false);
-  DONE;
-  "
-)
-
-(define_expand "sibcall_epilogue"
-  [(clobber (const_int 0))]
-  ""
-  "
-  aarch64_expand_epilogue (true);
+  aarch64_expand_epilogue (nullptr);
   DONE;
   "
 )
diff --git a/gcc/doc/gccint/target-macros/miscellaneous-parameters.rst b/gcc/doc/gccint/target-macros/miscellaneous-parameters.rst
index b48f91d3fd2..29d6b87b3c3 100644
--- a/gcc/doc/gccint/target-macros/miscellaneous-parameters.rst
+++ b/gcc/doc/gccint/target-macros/miscellaneous-parameters.rst
@@ -556,6 +556,11 @@ Here are several miscellaneous parameters.
   :end-before: [TARGET_USE_LATE_PROLOGUE_EPILOGUE]
 
 
+.. include:: tm.rst.in
+  :start-after: [TARGET_EMIT_EPILOGUE_FOR_SIBCALL]
+  :end-before: [TARGET_EMIT_EPILOGUE_FOR_SIBCALL]
+
+
 .. include:: tm.rst.in
   :start-after: [TARGET_MACHINE_DEPENDENT_REORG]
   :end-before: [TARGET_MACHINE_DEPENDENT_REORG]
diff --git a/gcc/doc/gccint/target-macros/tm.rst.in b/gcc/doc/gccint/target-macros/tm.rst.in
index 2e789f8723d..a19fa38b811 100644
--- a/gcc/doc/gccint/target-macros/tm.rst.in
+++ b/gcc/doc/gccint/target-macros/tm.rst.in
@@ -3724,6 +3724,17 @@
 
 [TARGET_USE_LATE_PROLOGUE_EPILOGUE]
 
+[TARGET_EMIT_EPILOGUE_FOR_SIBCALL]
+.. function:: void TARGET_EMIT_EPILOGUE_FOR_SIBCALL (rtx_call_insn *call)
+
+  If defined, this hook emits an epilogue sequence for sibling (tail)
+  call instruction :samp:`call`.  Another way of providing epilogues
+  for sibling calls is to define the ``sibcall_epilogue`` instruction
+  pattern; the main advantage of this hook over the pattern is that it
+  has access to the call instruction.
+
+[TARGET_EMIT_EPILOGUE_FOR_SIBCALL]
+
 [TARGET_MACHINE_DEPENDENT_REORG]
 .. function:: void TARGET_MACHINE_DEPENDENT_REORG (void)
 
diff --git a/gcc/function.cc b/gcc/function.cc
index 3b1ab5d09e5..ecd656da332 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -6224,7 +6224,17 @@ thread_prologue_and_epilogue_insns (void)
       if (!(CALL_P (insn) && SIBLING_CALL_P (insn)))
 	continue;
 
-      if (rtx_insn *ep_seq = targetm.gen_sibcall_epilogue ())
+      rtx_insn *ep_seq;
+      if (targetm.emit_epilogue_for_sibcall)
+	{
+	  start_sequence ();
+	  targetm.emit_epilogue_for_sibcall (as_a<rtx_call_insn *> (insn));
+	  ep_seq = get_insns ();
+	  end_sequence ();
+	}
+      else
+	ep_seq = targetm.gen_sibcall_epilogue ();
+      if (ep_seq)
 	{
 	  start_sequence ();
 	  emit_note (NOTE_INSN_EPILOGUE_BEG);
@@ -6284,7 +6294,8 @@ reposition_prologue_and_epilogue_notes (void)
 {
   if (!targetm.have_prologue ()
       && !targetm.have_epilogue ()
-      && !targetm.have_sibcall_epilogue ())
+      && !targetm.have_sibcall_epilogue ()
+      && !targetm.emit_epilogue_for_sibcall)
     return;
 
   /* Since the hash table is created on demand, the fact that it is
diff --git a/gcc/target.def b/gcc/target.def
index 8b8aef982e8..15fd939200b 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -4083,6 +4083,15 @@ between instruction sets.",
  bool, (),
  hook_bool_void_false)
 
+DEFHOOK
+(emit_epilogue_for_sibcall,
+ "If defined, this hook emits an epilogue sequence for sibling (tail)\n\
+call instruction :samp:`call`.  Another way of providing epilogues\n\
+for sibling calls is to define the ``sibcall_epilogue`` instruction\n\
+pattern; the main advantage of this hook over the pattern is that it\n\
+has access to the call instruction.",
+ void, (rtx_call_insn *call), NULL)
+
 /* Do machine-dependent code transformations.  Called just before
      delayed-branch scheduling.  */
 DEFHOOK
-- 
2.25.1

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

[Jeff Law]

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

[PATCH] Add a target hook for sibcall epilogues

[Richard Sandiford]

Jeff approved this patch last year (thanks!):
https://gcc.gnu.org/pipermail/gcc-patches/2022-November/606362.html
I ended up not pushing it then because the things that used it didn't
go in.  Now pushed after retesting on aarch64-linux-gnu.

---

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).

gcc/
	* doc/tm.texi.in: Add TARGET_EMIT_EPILOGUE_FOR_SIBCALL.
	* doc/tm.texi: 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.
---
 gcc/calls.cc                        |  3 ++-
 gcc/config/aarch64/aarch64-protos.h |  2 +-
 gcc/config/aarch64/aarch64.cc       | 11 +++++++----
 gcc/config/aarch64/aarch64.md       | 11 +----------
 gcc/doc/tm.texi                     |  8 ++++++++
 gcc/doc/tm.texi.in                  |  2 ++
 gcc/function.cc                     | 15 +++++++++++++--
 gcc/target.def                      |  9 +++++++++
 8 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/gcc/calls.cc b/gcc/calls.cc
index 9edb5831611..cc4210cd456 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -2502,7 +2502,8 @@ can_implement_as_sibling_call_p (tree exp,
 				 tree addr,
 				 const args_size &args_size)
 {
-  if (!targetm.have_sibcall_epilogue ())
+  if (!targetm.have_sibcall_epilogue ()
+      && !targetm.emit_epilogue_for_sibcall)
     {
       maybe_complain_about_tail_call
 	(exp,
diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
index d2718cc87b3..b0b7d33714d 100644
--- a/gcc/config/aarch64/aarch64-protos.h
+++ b/gcc/config/aarch64/aarch64-protos.h
@@ -888,7 +888,7 @@ const char * aarch64_gen_far_branch (rtx *, int, const char *, const char *);
 const char * aarch64_output_probe_stack_range (rtx, rtx);
 const char * aarch64_output_probe_sve_stack_clash (rtx, rtx, rtx, rtx);
 void aarch64_err_no_fpadvsimd (machine_mode);
-void aarch64_expand_epilogue (bool);
+void aarch64_expand_epilogue (rtx_call_insn *);
 rtx aarch64_ptrue_all (unsigned int);
 opt_machine_mode aarch64_ptrue_all_mode (rtx);
 rtx aarch64_convert_sve_data_to_pred (rtx, machine_mode, rtx);
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index fca64daf2a0..c864f4c0f6f 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -7971,7 +7971,7 @@ aarch64_use_return_insn_p (void)
    from a deallocated stack, and we optimize the unwind records by
    emitting them all together if possible.  */
 void
-aarch64_expand_epilogue (bool for_sibcall)
+aarch64_expand_epilogue (rtx_call_insn *sibcall)
 {
   aarch64_frame &frame = cfun->machine->frame;
   poly_int64 initial_adjust = frame.initial_adjust;
@@ -8102,7 +8102,7 @@ aarch64_expand_epilogue (bool for_sibcall)
     }
 
   /* Stack adjustment for exception handler.  */
-  if (crtl->calls_eh_return && !for_sibcall)
+  if (crtl->calls_eh_return && !sibcall)
     {
       /* If the EH_RETURN_TAKEN_RTX flag is set then we need
 	 to unwind the stack and jump to the handler, otherwise
@@ -8137,7 +8137,7 @@ aarch64_expand_epilogue (bool for_sibcall)
 	   explicitly authenticate.
     */
   if (aarch64_return_address_signing_enabled ()
-      && (for_sibcall || !TARGET_ARMV8_3))
+      && (sibcall || !TARGET_ARMV8_3))
     {
       switch (aarch_ra_sign_key)
 	{
@@ -8155,7 +8155,7 @@ aarch64_expand_epilogue (bool for_sibcall)
     }
 
   emit_use (gen_rtx_REG (DImode, LR_REGNUM));
-  if (!for_sibcall)
+  if (!sibcall)
     emit_jump_insn (ret_rtx);
 }
 
@@ -26427,6 +26427,9 @@ aarch64_libgcc_floating_mode_supported_p
 #undef TARGET_CONST_ANCHOR
 #define TARGET_CONST_ANCHOR 0x1000000
 
+#undef TARGET_EMIT_EPILOGUE_FOR_SIBCALL
+#define TARGET_EMIT_EPILOGUE_FOR_SIBCALL aarch64_expand_epilogue
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-aarch64.h"
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 4a3af6df7e7..202190c2cbf 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -863,16 +863,7 @@ (define_expand "epilogue"
   [(clobber (const_int 0))]
   ""
   "
-  aarch64_expand_epilogue (false);
-  DONE;
-  "
-)
-
-(define_expand "sibcall_epilogue"
-  [(clobber (const_int 0))]
-  ""
-  "
-  aarch64_expand_epilogue (true);
+  aarch64_expand_epilogue (nullptr);
   DONE;
   "
 )
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 6709c42a48f..bc8ee04d7d5 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -11898,6 +11898,14 @@ the hook might return true if the prologue and epilogue need to switch
 between instruction sets.
 @end deftypefn
 
+@deftypefn {Target Hook} void TARGET_EMIT_EPILOGUE_FOR_SIBCALL (rtx_call_insn *@var{call})
+If defined, this hook emits an epilogue sequence for sibling (tail)
+call instruction @var{call}.  Another way of providing epilogues
+for sibling calls is to define the @code{sibcall_epilogue} instruction
+pattern; the main advantage of this hook over the pattern is that it
+has access to the call instruction.
+@end deftypefn
+
 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG (void)
 If non-null, this hook performs a target-specific pass over the
 instruction stream.  The compiler will run it at all optimization levels,
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index d1d7cfafdca..5f636abf9fc 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7786,6 +7786,8 @@ to by @var{ce_info}.
 
 @hook TARGET_USE_LATE_PROLOGUE_EPILOGUE
 
+@hook TARGET_EMIT_EPILOGUE_FOR_SIBCALL
+
 @hook TARGET_MACHINE_DEPENDENT_REORG
 
 @hook TARGET_INIT_BUILTINS
diff --git a/gcc/function.cc b/gcc/function.cc
index 704930160c3..89841787ff8 100644
--- a/gcc/function.cc
+++ b/gcc/function.cc
@@ -6208,7 +6208,17 @@ thread_prologue_and_epilogue_insns (void)
       if (!(CALL_P (insn) && SIBLING_CALL_P (insn)))
 	continue;
 
-      if (rtx_insn *ep_seq = targetm.gen_sibcall_epilogue ())
+      rtx_insn *ep_seq;
+      if (targetm.emit_epilogue_for_sibcall)
+	{
+	  start_sequence ();
+	  targetm.emit_epilogue_for_sibcall (as_a<rtx_call_insn *> (insn));
+	  ep_seq = get_insns ();
+	  end_sequence ();
+	}
+      else
+	ep_seq = targetm.gen_sibcall_epilogue ();
+      if (ep_seq)
 	{
 	  start_sequence ();
 	  emit_note (NOTE_INSN_EPILOGUE_BEG);
@@ -6268,7 +6278,8 @@ reposition_prologue_and_epilogue_notes (void)
 {
   if (!targetm.have_prologue ()
       && !targetm.have_epilogue ()
-      && !targetm.have_sibcall_epilogue ())
+      && !targetm.have_sibcall_epilogue ()
+      && !targetm.emit_epilogue_for_sibcall)
     return;
 
   /* Since the hash table is created on demand, the fact that it is
diff --git a/gcc/target.def b/gcc/target.def
index 04715028460..427fe526b5a 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -4174,6 +4174,15 @@ between instruction sets.",
  bool, (),
  hook_bool_void_false)
 
+DEFHOOK
+(emit_epilogue_for_sibcall,
+ "If defined, this hook emits an epilogue sequence for sibling (tail)\n\
+call instruction @var{call}.  Another way of providing epilogues\n\
+for sibling calls is to define the @code{sibcall_epilogue} instruction\n\
+pattern; the main advantage of this hook over the pattern is that it\n\
+has access to the call instruction.",
+ void, (rtx_call_insn *call), NULL)
+
 /* Do machine-dependent code transformations.  Called just before
      delayed-branch scheduling.  */
 DEFHOOK
-- 
2.25.1