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[PATCH] Make sibcall argument overlap check less pessimistic (PR middle-end/50074)


Hi!

Kirill's recent change to mem_overlaps_already_clobbered_arg_p
resulted in various code quality regressions, many calls that used
to be tail call optimized no longer are.

Here is an attempt to make the check more complete (e.g.
the change wouldn't see overlap if addr was PLUS of two REGs,
where one of the REGs was based on internal_arg_pointer, etc.)
and less pessimistic.  As tree-tailcall.c doesn't allow tail calls
from functions that have address of any of the caller's parameters
taken, IMHO it is enough to look for internal_arg_pointer based
pseudos initialized in the tail call sequence.
This patch scans the tail call sequence and notes which pseudos
are based on internal_arg_pointer (and what offset from
that pointer they have) and uses that in
mem_overlaps_already_clobbered_arg_p.

Bootstrapped/regtested on x86_64-linux and i686-linux, tested on some
testcases on ia64-linux (as an example of target which doesn't have
reg + disp addressing and thus forces everything into registers).
Ok for trunk?

2011-11-25  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/50074
	* calls.c (internal_arg_pointer_seq_start,
	internal_arg_pointer_cache): New variables.
	(internal_arg_pointer_based_reg_1): New function.
	(internal_arg_pointer_based_reg): New function.
	(mem_overlaps_already_clobbered_arg_p): Use it.
	(expand_call): Free internal_arg_pointer_cache vector
	and clear internal_arg_pointer_seq_start.

--- gcc/calls.c.jj	2011-11-08 23:35:12.000000000 +0100
+++ gcc/calls.c	2011-11-25 17:24:52.445878841 +0100
@@ -1658,6 +1658,106 @@ rtx_for_function_call (tree fndecl, tree
   return funexp;
 }
 
+/* Last insn that has been already scanned by internal_arg_pointer_based_reg,
+   or NULL_RTX if none has been scanned yet.  */
+static rtx internal_arg_pointer_seq_start;
+/* Vector indexed by REGNO () - FIRST_PSEUDO_REGISTER, recoding if a pseudo
+   is based on crtl->args.internal_arg_pointer.  It is NULL_RTX if not based
+   on it, some CONST_INT as offset from crtl->args.internal_arg_pointer
+   or PC for unknown offset from it.  */
+static VEC(rtx, heap) *internal_arg_pointer_cache;
+
+static rtx internal_arg_pointer_based_reg (rtx, bool);
+
+/* Helper function for internal_arg_pointer_based_reg, called through
+   for_each_rtx.  Return 1 if a crtl->args.internal_arg_pointer based
+   register is seen anywhere.  */
+
+static int
+internal_arg_pointer_based_reg_1 (rtx *loc, void *data ATTRIBUTE_UNUSED)
+{
+  if (REG_P (*loc) && internal_arg_pointer_based_reg (*loc, false) != NULL_RTX)
+    return 1;
+  if (MEM_P (*loc))
+    return -1;
+  return 0;
+}
+
+/* If REG is based on crtl->args.internal_arg_pointer, return either
+   a CONST_INT offset from crtl->args.internal_arg_pointer if
+   offset from it is known constant, or PC if the offset is unknown.
+   Return NULL_RTX if REG isn't based on crtl->args.internal_arg_pointer.  */
+
+static rtx
+internal_arg_pointer_based_reg (rtx reg, bool scan)
+{
+  rtx insn;
+
+  if (CONSTANT_P (reg))
+    return NULL_RTX;
+
+  if (reg == crtl->args.internal_arg_pointer)
+    return const0_rtx;
+
+  if (REG_P (reg) && REGNO (reg) < FIRST_PSEUDO_REGISTER)
+    return NULL_RTX;
+
+  if (GET_CODE (reg) == PLUS && CONST_INT_P (XEXP (reg, 1)))
+    {
+      rtx val = internal_arg_pointer_based_reg (XEXP (reg, 0), scan);
+      if (val == NULL_RTX || val == pc_rtx)
+	return val;
+      return plus_constant (val, INTVAL (XEXP (reg, 1)));
+    }
+
+  if (!scan)
+    insn = NULL_RTX;
+  else if (internal_arg_pointer_seq_start == NULL_RTX)
+    insn = get_insns ();
+  else
+    insn = NEXT_INSN (internal_arg_pointer_seq_start);
+  while (insn)
+    {
+      rtx set = single_set (insn);
+      if (set
+	  && REG_P (SET_DEST (set))
+	  && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER)
+	{
+	  rtx val = NULL_RTX;
+	  unsigned int idx = REGNO (SET_DEST (set)) - FIRST_PSEUDO_REGISTER;
+	  /* Punt on pseudos set multiple times.  */
+	  if (idx < VEC_length (rtx, internal_arg_pointer_cache)
+	      && VEC_index (rtx, internal_arg_pointer_cache, idx)
+		 != NULL_RTX)
+	    val = pc_rtx;
+	  else
+	    val = internal_arg_pointer_based_reg (SET_SRC (set), false);
+	  if (val != NULL_RTX)
+	    {
+	      VEC_safe_grow_cleared (rtx, heap, internal_arg_pointer_cache,
+				     idx + 1);
+	      VEC_replace (rtx, internal_arg_pointer_cache, idx, val);
+	    }
+	}
+      if (NEXT_INSN (insn) == NULL_RTX)
+	internal_arg_pointer_seq_start = insn;
+      insn = NEXT_INSN (insn);
+    }
+
+  if (REG_P (reg))
+    {
+      unsigned int idx = REGNO (reg) - FIRST_PSEUDO_REGISTER;
+      if (idx < VEC_length (rtx, internal_arg_pointer_cache))
+	return VEC_index (rtx, internal_arg_pointer_cache, idx);
+      else
+	return NULL_RTX;
+    }
+
+  if (for_each_rtx (&reg, internal_arg_pointer_based_reg_1, NULL))
+    return pc_rtx;
+  return NULL_RTX;
+}
+
 /* Return true if and only if SIZE storage units (usually bytes)
    starting from address ADDR overlap with already clobbered argument
    area.  This function is used to determine if we should give up a
@@ -1667,24 +1767,15 @@ static bool
 mem_overlaps_already_clobbered_arg_p (rtx addr, unsigned HOST_WIDE_INT size)
 {
   HOST_WIDE_INT i;
+  rtx val;
 
-  if (addr == crtl->args.internal_arg_pointer)
-    i = 0;
-  else if (GET_CODE (addr) == PLUS
-	   && XEXP (addr, 0) == crtl->args.internal_arg_pointer
-	   && CONST_INT_P (XEXP (addr, 1)))
-    i = INTVAL (XEXP (addr, 1));
-  /* Return true for arg pointer based indexed addressing.  */
-  else if (GET_CODE (addr) == PLUS
-	   && (XEXP (addr, 0) == crtl->args.internal_arg_pointer
-	       || XEXP (addr, 1) == crtl->args.internal_arg_pointer))
-    return true;
-  /* If the address comes in a register, we have no idea of its origin so
-     give up and conservatively return true.  */
-  else if (REG_P(addr))
+  val = internal_arg_pointer_based_reg (addr, true);
+  if (val == NULL_RTX)
+    return false;
+  else if (val == pc_rtx)
     return true;
   else
-    return false;
+    i = INTVAL (val);
 
 #ifdef ARGS_GROW_DOWNWARD
   i = -i - size;
@@ -3292,6 +3383,8 @@ expand_call (tree exp, rtx target, int i
 	    }
 
 	  sbitmap_free (stored_args_map);
+	  internal_arg_pointer_seq_start = NULL_RTX;
+	  VEC_free (rtx, heap, internal_arg_pointer_cache);
 	}
       else
 	{

	Jakub


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