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* [PATCH] Add a new target hook to compute the frame layout
@ 2016-06-16 14:47 Bernd Edlinger
  2016-06-21 21:30 ` Jeff Law
  0 siblings, 1 reply; 15+ messages in thread
From: Bernd Edlinger @ 2016-06-16 14:47 UTC (permalink / raw)
  To: gcc-patches
  Cc: Richard Biener, Jakub Jelinek, Richard Sandiford,
	Ramana Radhakrishnan, Jeff Law

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Hi!


By the design of the target hook INITIAL_ELIMINATION_OFFSET
it is necessary to call this function several times with
different register combinations.
Most targets use a cached data structure that describes the
exact frame layout of the current function.

It is safe to skip the computation when reload_completed = true,
and most targets do that already.

However while reload is doing its work, it is not clear when to
do the computation and when not.  This results in unnecessary
work.  Computing the frame layout can be a simple function or an
arbitrarily complex one, that walks all instructions of the current
function for instance, which is more or less the common case.


This patch adds a new optional target hook that can be used
by the target to factor the INITIAL_ELIMINATION_OFFSET-hook
into a O(n) computation part, and a O(1) result function.

The patch implements a compute_frame_layout target hook just
for ARM in the moment, to show the principle.
Other targets may also implement that hook, if it seems appropriate.


Boot-strapped and reg-tested on arm-linux-gnueabihf.
OK for trunk?


Thanks
Bernd.

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2016-06-16  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* target.def (compute_frame_layout): New optional target hook.
	* doc/tm.texi.in (TARGET_COMPUTE_FRAME_LAYOUT): Add hook.
	* doc/tm.texi (TARGET_COMPUTE_FRAME_LAYOUT): Add documentation.
	* lra-eliminations.c (update_reg_eliminate): Call compute_frame_layout
	target hook.
	* reload1.c (verify_initial_elim_offsets): Likewise.
	* config/arm/arm.c (TARGET_COMPUTE_FRAME_LAYOUT): Define.
	(use_simple_return_p): Call arm_compute_frame_layout if needed.
	(arm_get_frame_offsets): Split up into this ...
	(arm_compute_frame_layout): ... and this function.

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Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c	(Revision 233176)
+++ gcc/config/arm/arm.c	(Arbeitskopie)
@@ -81,6 +81,7 @@ static bool arm_const_not_ok_for_debug_p (rtx);
 static bool arm_needs_doubleword_align (machine_mode, const_tree);
 static int arm_compute_static_chain_stack_bytes (void);
 static arm_stack_offsets *arm_get_frame_offsets (void);
+static void arm_compute_frame_layout (void);
 static void arm_add_gc_roots (void);
 static int arm_gen_constant (enum rtx_code, machine_mode, rtx,
 			     unsigned HOST_WIDE_INT, rtx, rtx, int, int);
@@ -669,6 +670,9 @@ static const struct attribute_spec arm_attribute_t
 #undef TARGET_SCALAR_MODE_SUPPORTED_P
 #define TARGET_SCALAR_MODE_SUPPORTED_P arm_scalar_mode_supported_p
 
+#undef TARGET_COMPUTE_FRAME_LAYOUT
+#define TARGET_COMPUTE_FRAME_LAYOUT arm_compute_frame_layout
+
 #undef TARGET_FRAME_POINTER_REQUIRED
 #define TARGET_FRAME_POINTER_REQUIRED arm_frame_pointer_required
 
@@ -3813,6 +3817,10 @@ use_simple_return_p (void)
 {
   arm_stack_offsets *offsets;
 
+  /* Note this function can be called before or after reload.  */
+  if (!reload_completed)
+    arm_compute_frame_layout ();
+
   offsets = arm_get_frame_offsets ();
   return offsets->outgoing_args != 0;
 }
@@ -19238,7 +19246,7 @@ arm_compute_static_chain_stack_bytes (void)
 
 /* Compute a bit mask of which registers need to be
    saved on the stack for the current function.
-   This is used by arm_get_frame_offsets, which may add extra registers.  */
+   This is used by arm_compute_frame_layout, which may add extra registers.  */
 
 static unsigned long
 arm_compute_save_reg_mask (void)
@@ -20789,12 +20797,25 @@ any_sibcall_could_use_r3 (void)
   alignment.  */
 
 
+/* Return cached stack offsets.  */
+
+static arm_stack_offsets *
+arm_get_frame_offsets (void)
+{
+  struct arm_stack_offsets *offsets;
+
+  offsets = &cfun->machine->stack_offsets;
+
+  return offsets;
+}
+
+
 /* Calculate stack offsets.  These are used to calculate register elimination
    offsets and in prologue/epilogue code.  Also calculates which registers
    should be saved.  */
 
-static arm_stack_offsets *
-arm_get_frame_offsets (void)
+static void
+arm_compute_frame_layout (void)
 {
   struct arm_stack_offsets *offsets;
   unsigned long func_type;
@@ -20806,19 +20827,6 @@ any_sibcall_could_use_r3 (void)
 
   offsets = &cfun->machine->stack_offsets;
 
-  /* We need to know if we are a leaf function.  Unfortunately, it
-     is possible to be called after start_sequence has been called,
-     which causes get_insns to return the insns for the sequence,
-     not the function, which will cause leaf_function_p to return
-     the incorrect result.
-
-     to know about leaf functions once reload has completed, and the
-     frame size cannot be changed after that time, so we can safely
-     use the cached value.  */
-
-  if (reload_completed)
-    return offsets;
-
   /* Initially this is the size of the local variables.  It will translated
      into an offset once we have determined the size of preceding data.  */
   frame_size = ROUND_UP_WORD (get_frame_size ());
@@ -20885,7 +20893,7 @@ any_sibcall_could_use_r3 (void)
     {
       offsets->outgoing_args = offsets->soft_frame;
       offsets->locals_base = offsets->soft_frame;
-      return offsets;
+      return;
     }
 
   /* Ensure SFP has the correct alignment.  */
@@ -20961,8 +20969,6 @@ any_sibcall_could_use_r3 (void)
 	offsets->outgoing_args += 4;
       gcc_assert (!(offsets->outgoing_args & 7));
     }
-
-  return offsets;
 }
 
 
Index: gcc/doc/tm.texi
===================================================================
--- gcc/doc/tm.texi	(Revision 233176)
+++ gcc/doc/tm.texi	(Arbeitskopie)
@@ -3693,6 +3693,14 @@ registers.  This macro must be defined if @code{EL
 defined.
 @end defmac
 
+@deftypefn {Target Hook} void TARGET_COMPUTE_FRAME_LAYOUT (void)
+This target hook is called immediately before reload wants to call
+@code{INITIAL_ELIMINATION_OFFSET} and allows the target to cache the frame
+layout instead of re-computing it on every invocation.  This is particularly
+useful for targets that have an O(n) frame layout function.  Implementing
+this callback is optional.
+@end deftypefn
+
 @node Stack Arguments
 @subsection Passing Function Arguments on the Stack
 @cindex arguments on stack
Index: gcc/doc/tm.texi.in
===================================================================
--- gcc/doc/tm.texi.in	(Revision 233176)
+++ gcc/doc/tm.texi.in	(Arbeitskopie)
@@ -3227,6 +3227,8 @@ registers.  This macro must be defined if @code{EL
 defined.
 @end defmac
 
+@hook TARGET_COMPUTE_FRAME_LAYOUT
+
 @node Stack Arguments
 @subsection Passing Function Arguments on the Stack
 @cindex arguments on stack
Index: gcc/lra-eliminations.c
===================================================================
--- gcc/lra-eliminations.c	(Revision 233176)
+++ gcc/lra-eliminations.c	(Arbeitskopie)
@@ -1202,6 +1202,10 @@ update_reg_eliminate (bitmap insns_with_changed_of
   struct lra_elim_table *ep, *ep1;
   HARD_REG_SET temp_hard_reg_set;
 
+#ifdef ELIMINABLE_REGS
+  targetm.compute_frame_layout ();
+#endif
+
   /* Clear self elimination offsets.  */
   for (ep = reg_eliminate; ep < &reg_eliminate[NUM_ELIMINABLE_REGS]; ep++)
     self_elim_offsets[ep->from] = 0;
Index: gcc/reload1.c
===================================================================
--- gcc/reload1.c	(Revision 233176)
+++ gcc/reload1.c	(Arbeitskopie)
@@ -3856,6 +3856,7 @@ verify_initial_elim_offsets (void)
   {
    struct elim_table *ep;
 
+   targetm.compute_frame_layout ();
    for (ep = reg_eliminate; ep < &reg_eliminate[NUM_ELIMINABLE_REGS]; ep++)
      {
        INITIAL_ELIMINATION_OFFSET (ep->from, ep->to, t);
@@ -3880,6 +3881,7 @@ set_initial_elim_offsets (void)
   struct elim_table *ep = reg_eliminate;
 
 #ifdef ELIMINABLE_REGS
+  targetm.compute_frame_layout ();
   for (; ep < &reg_eliminate[NUM_ELIMINABLE_REGS]; ep++)
     {
       INITIAL_ELIMINATION_OFFSET (ep->from, ep->to, ep->initial_offset);
Index: gcc/target.def
===================================================================
--- gcc/target.def	(Revision 233176)
+++ gcc/target.def	(Arbeitskopie)
@@ -5245,8 +5245,19 @@ five otherwise.  This is best for most machines.",
  unsigned int, (void),
  default_case_values_threshold)
 
-/* Retutn true if a function must have and use a frame pointer.  */
+/* Optional callback to advise the target to compute the frame layout.  */
 DEFHOOK
+(compute_frame_layout,
+ "This target hook is called immediately before reload wants to call\n\
+@code{INITIAL_ELIMINATION_OFFSET} and allows the target to cache the frame\n\
+layout instead of re-computing it on every invocation.  This is particularly\n\
+useful for targets that have an O(n) frame layout function.  Implementing\n\
+this callback is optional.",
+ void, (void),
+ hook_void_void)
+
+/* Return true if a function must have and use a frame pointer.  */
+DEFHOOK
 (frame_pointer_required,
  "This target hook should return @code{true} if a function must have and use\n\
 a frame pointer.  This target hook is called in the reload pass.  If its return\n\

^ permalink raw reply	[flat|nested] 15+ messages in thread
end of thread, other threads:[~2017-05-06 18:07 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-06-16 14:47 [PATCH] Add a new target hook to compute the frame layout Bernd Edlinger
2016-06-21 21:30 ` Jeff Law
2016-06-22  5:12   ` Bernd Edlinger
2016-06-22  7:21     ` AW: " Bernd Edlinger
2016-06-22 18:34       ` Jeff Law
2016-06-22 18:49     ` Jeff Law
2016-06-22 20:25       ` Bernd Edlinger
2016-08-04 21:16   ` [PATCH, ARM] " Bernd Edlinger
2016-08-05  9:29     ` Richard Earnshaw (lists)
2016-08-05 12:49       ` Bernd Edlinger
2016-08-05 14:06         ` Richard Earnshaw (lists)
2016-08-05 15:23           ` Bernd Edlinger
2016-09-05 16:45           ` Bernd Edlinger
2017-05-05 15:02             ` Richard Earnshaw (lists)
2017-05-06 18:16               ` Bernd Edlinger

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