Patchwork fix for PR49888 var-tracking compile-time regression

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Submitter Alexandre Oliva
Date Jan. 17, 2013, 8:56 p.m.
Message ID <or4nif1qbb.fsf@livre.localdomain>
Download mbox | patch
Permalink /patch/213363/
State New
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Comments

Alexandre Oliva - Jan. 17, 2013, 8:56 p.m.
On Jan 16, 2013, Jakub Jelinek <jakub@redhat.com> wrote:

> for i686-linux tree-ssa-pre.o is different, and
> for x86_64-linux go/export.o is different.

I looked into the latter first, and that revealed a few major bugs:

1. I'd failed to fully implement what I'd planned.  The canonicalization
function would still take REGs from dataflow sets, instead of only
VALUEs that can be safely cached, and the memory clobbering was still
using an expression that could contain REGs rather than only VALUEs.
This means at times the canonical values could have been wrong, and they
could accidentally fail to match.

2. ENTRY_VALUEs, that could already be used as canonical base addresses
before, have now become far more likely to be chosen as such, but the
alias code compared all ENTRY_VALUEs of the same mode equal, because the
ENTRY_VALUE operand is a 0 rather than an e.

Having fixed these two problems, the debug info for go/export became
identical.  Feeling adventurous, I made all memory overlap tests
performed as part of the memory clobbering use (the nwo cheap)
canonicalized addresses, instead of only canonicalizing the compare-with
addresses that were marked as SP-based.

This gives us additional accuracy in the tests, and this caused some
additional differences in tree-ssa-pre compare on i686: with the earlier
patch, we'd fail to recognize many compares as non-overlapping, and
conservatively drop the corresponding MEMs from the dataflow set.  In
other cases, it was the use of VALUE-based address canonicalization that
enabled the mem conflict test to do a better job.

While investigating this, I found out we'd go TWICE over the entire
dataflow set clobbering each modified MEM, when once would have been
enough, and fixed that too.  This should further reduce the performance
impact caused by the original memory clobbering patch.

Here's the patch I've just regstrapped.  Test results look good, with no
regressions introduced since the earlier version of the patch, which
itself hadn't regressed on top of an earlier tree.  However, there are
regressions comparing the latest results with those based on the earlier
tree, so I'm now running a baseline test just to be sure that the
regressions are not caused by this patch.  Ok to install if they aren't?
Jakub Jelinek - Jan. 18, 2013, 10:58 a.m.
On Thu, Jan 17, 2013 at 06:56:40PM -0200, Alexandre Oliva wrote:
> From: Alexandre Oliva <aoliva@redhat.com>
> 
> for  gcc/ChangeLog
> 
> 	PR debug/54114
> 	PR debug/54402
> 	PR debug/49888
> 	* var-tracking.c (negative_power_of_two_p): New.
> 	(global_get_addr_cache, local_get_addr_cache): New.
> 	(get_addr_from_global_cache, get_addr_from_local_cache): New.
> 	(vt_canonicalize_addr): Rewrite using the above.  Adjust the
> 	heading comment.
> 	(vt_stack_offset_p): Remove.
> 	(vt_canon_true_dep): Always canonicalize loc's address.
> 	(clobber_overlapping_mems): Make sure we have a MEM.
> 	(local_get_addr_clear_given_value): New.
> 	(val_reset): Clear local cached entries.
> 	(compute_bb_dataflow): Create and release the local cache.
> 	Disable duplicate MEMs clobbering.
> 	(emit_notes_in_bb): Clobber MEMs likewise.
> 	(vt_emit_notes): Create and release the local cache.
> 	(vt_initialize, vt_finalize): Create and release the global
> 	cache, respectively.
> 	* alias.c (rtx_equal_for_memref_p): Compare operands of
> 	ENTRY_VALUEs.

Ok, thanks.

	Jakub

Patch

Cache canonical addresses within VTA

From: Alexandre Oliva <aoliva@redhat.com>

for  gcc/ChangeLog

	PR debug/54114
	PR debug/54402
	PR debug/49888
	* var-tracking.c (negative_power_of_two_p): New.
	(global_get_addr_cache, local_get_addr_cache): New.
	(get_addr_from_global_cache, get_addr_from_local_cache): New.
	(vt_canonicalize_addr): Rewrite using the above.  Adjust the
	heading comment.
	(vt_stack_offset_p): Remove.
	(vt_canon_true_dep): Always canonicalize loc's address.
	(clobber_overlapping_mems): Make sure we have a MEM.
	(local_get_addr_clear_given_value): New.
	(val_reset): Clear local cached entries.
	(compute_bb_dataflow): Create and release the local cache.
	Disable duplicate MEMs clobbering.
	(emit_notes_in_bb): Clobber MEMs likewise.
	(vt_emit_notes): Create and release the local cache.
	(vt_initialize, vt_finalize): Create and release the global
	cache, respectively.
	* alias.c (rtx_equal_for_memref_p): Compare operands of
	ENTRY_VALUEs.
---

 gcc/alias.c        |    4 +
 gcc/var-tracking.c |  293 ++++++++++++++++++++++++++++++++++++++++------------
 2 files changed, 231 insertions(+), 66 deletions(-)


diff --git a/gcc/alias.c b/gcc/alias.c
index f3cd014..e18dd34 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -1465,6 +1465,10 @@  rtx_equal_for_memref_p (const_rtx x, const_rtx y)
     case SYMBOL_REF:
       return XSTR (x, 0) == XSTR (y, 0);
 
+    case ENTRY_VALUE:
+      /* This is magic, don't go through canonicalization et al.  */
+      return rtx_equal_p (ENTRY_VALUE_EXP (x), ENTRY_VALUE_EXP (y));
+
     case VALUE:
     CASE_CONST_UNIQUE:
       /* There's no need to compare the contents of CONST_DOUBLEs or
diff --git a/gcc/var-tracking.c b/gcc/var-tracking.c
index def624a..714acb69 100644
--- a/gcc/var-tracking.c
+++ b/gcc/var-tracking.c
@@ -1948,6 +1948,14 @@  var_regno_delete (dataflow_set *set, int regno)
   *reg = NULL;
 }
 
+/* Return true if I is the negated value of a power of two.  */
+static bool
+negative_power_of_two_p (HOST_WIDE_INT i)
+{
+  unsigned HOST_WIDE_INT x = -(unsigned HOST_WIDE_INT)i;
+  return x == (x & -x);
+}
+
 /* Strip constant offsets and alignments off of LOC.  Return the base
    expression.  */
 
@@ -1958,83 +1966,191 @@  vt_get_canonicalize_base (rtx loc)
 	  || GET_CODE (loc) == AND)
 	 && GET_CODE (XEXP (loc, 1)) == CONST_INT
 	 && (GET_CODE (loc) != AND
-	     || INTVAL (XEXP (loc, 1)) < 0))
+	     || negative_power_of_two_p (INTVAL (XEXP (loc, 1)))))
     loc = XEXP (loc, 0);
 
   return loc;
 }
 
+/* This caches canonicalized addresses for VALUEs, computed using
+   information in the global cselib table.  */
+static struct pointer_map_t *global_get_addr_cache;
+
+/* This caches canonicalized addresses for VALUEs, computed using
+   information from the global cache and information pertaining to a
+   basic block being analyzed.  */
+static struct pointer_map_t *local_get_addr_cache;
+
+static rtx vt_canonicalize_addr (dataflow_set *, rtx);
+
+/* Return the canonical address for LOC, that must be a VALUE, using a
+   cached global equivalence or computing it and storing it in the
+   global cache.  */
+
+static rtx
+get_addr_from_global_cache (rtx const loc)
+{
+  rtx x;
+  void **slot;
+
+  gcc_checking_assert (GET_CODE (loc) == VALUE);
+  
+  slot = pointer_map_insert (global_get_addr_cache, loc);
+  if (*slot)
+    return (rtx)*slot;
+
+  x = canon_rtx (get_addr (loc));
+
+  /* Tentative, avoiding infinite recursion.  */
+  *slot = x;
+
+  if (x != loc)
+    {
+      rtx nx = vt_canonicalize_addr (NULL, x);
+      if (nx != x)
+	{
+	  /* The table may have moved during recursion, recompute
+	     SLOT.  */
+	  slot = pointer_map_contains (global_get_addr_cache, loc);
+	  *slot = x = nx;
+	}
+    }
+
+  return x;
+}
+
+/* Return the canonical address for LOC, that must be a VALUE, using a
+   cached local equivalence or computing it and storing it in the
+   local cache.  */
+
+static rtx
+get_addr_from_local_cache (dataflow_set *set, rtx const loc)
+{
+  rtx x;
+  void **slot;
+  decl_or_value dv;
+  variable var;
+  location_chain l;
+
+  gcc_checking_assert (GET_CODE (loc) == VALUE);
+  
+  slot = pointer_map_insert (local_get_addr_cache, loc);
+  if (*slot)
+    return (rtx)*slot;
+
+  x = get_addr_from_global_cache (loc);
+  
+  /* Tentative, avoiding infinite recursion.  */
+  *slot = x;
+
+  /* Recurse to cache local expansion of X, or if we need to search
+     for a VALUE in the expansion.  */
+  if (x != loc)
+    {
+      rtx nx = vt_canonicalize_addr (set, x);
+      if (nx != x)
+	{
+	  slot = pointer_map_contains (local_get_addr_cache, loc);
+	  *slot = x = nx;
+	}
+      return x;
+    }
+
+  dv = dv_from_rtx (x);
+  var = (variable) htab_find_with_hash (shared_hash_htab (set->vars),
+					dv, dv_htab_hash (dv));
+  if (!var)
+    return x;
+
+  /* Look for an improved equivalent expression.  */
+  for (l = var->var_part[0].loc_chain; l; l = l->next)
+    {
+      rtx base = vt_get_canonicalize_base (l->loc);
+      if (GET_CODE (base) == VALUE
+	  && canon_value_cmp (base, loc))
+	{
+	  rtx nx = vt_canonicalize_addr (set, l->loc);
+	  if (x != nx)
+	    {
+	      slot = pointer_map_contains (local_get_addr_cache, loc);
+	      *slot = x = nx;
+	    }
+	  break;
+	}
+    }
+
+  return x;
+}
+
 /* Canonicalize LOC using equivalences from SET in addition to those
-   in the cselib static table.  */
+   in the cselib static table.  It expects a VALUE-based expression,
+   and it will only substitute VALUEs with other VALUEs or
+   function-global equivalences, so that, if two addresses have base
+   VALUEs that are locally or globally related in ways that
+   memrefs_conflict_p cares about, they will both canonicalize to
+   expressions that have the same base VALUE.
+
+   The use of VALUEs as canonical base addresses enables the canonical
+   RTXs to remain unchanged globally, if they resolve to a constant,
+   or throughout a basic block otherwise, so that they can be cached
+   and the cache needs not be invalidated when REGs, MEMs or such
+   change.  */
 
 static rtx
 vt_canonicalize_addr (dataflow_set *set, rtx oloc)
 {
   HOST_WIDE_INT ofst = 0;
   enum machine_mode mode = GET_MODE (oloc);
-  rtx loc = canon_rtx (get_addr (oloc));
+  rtx loc = oloc;
+  rtx x;
+  bool retry = true;
 
-  /* Try to substitute a base VALUE for equivalent expressions as much
-     as possible.  The goal here is to expand stack-related addresses
-     to one of the stack base registers, so that we can compare
-     addresses for overlaps.  */
-  while (GET_CODE (vt_get_canonicalize_base (loc)) == VALUE)
+  while (retry)
     {
-      rtx x;
-      decl_or_value dv;
-      variable var;
-      location_chain l;
-
-      while (GET_CODE (loc) == PLUS)
+      while (GET_CODE (loc) == PLUS
+	     && GET_CODE (XEXP (loc, 1)) == CONST_INT)
 	{
 	  ofst += INTVAL (XEXP (loc, 1));
 	  loc = XEXP (loc, 0);
-	  continue;
 	}
 
       /* Alignment operations can't normally be combined, so just
 	 canonicalize the base and we're done.  We'll normally have
 	 only one stack alignment anyway.  */
-      if (GET_CODE (loc) == AND)
+      if (GET_CODE (loc) == AND
+	  && GET_CODE (XEXP (loc, 1)) == CONST_INT
+	  && negative_power_of_two_p (INTVAL (XEXP (loc, 1))))
 	{
 	  x = vt_canonicalize_addr (set, XEXP (loc, 0));
 	  if (x != XEXP (loc, 0))
 	    loc = gen_rtx_AND (mode, x, XEXP (loc, 1));
-	  loc = canon_rtx (get_addr (loc));
-	  break;
+	  retry = false;
 	}
 
-      x = canon_rtx (get_addr (loc));
-
-      /* We've made progress!  Start over.  */
-      if (x != loc || GET_CODE (x) != VALUE)
+      if (GET_CODE (loc) == VALUE)
 	{
-	  loc = x;
-	  continue;
-	}
-
-      dv = dv_from_rtx (x);
-      var = (variable) htab_find_with_hash (shared_hash_htab (set->vars),
-					    dv, dv_htab_hash (dv));
-      if (!var)
-	break;
+	  if (set)
+	    loc = get_addr_from_local_cache (set, loc);
+	  else
+	    loc = get_addr_from_global_cache (loc);
 
-      /* Look for an improved equivalent expression.  */
-      for (l = var->var_part[0].loc_chain; l; l = l->next)
-	{
-	  rtx base = vt_get_canonicalize_base (l->loc);
-	  if (GET_CODE (base) == REG
-	      || (GET_CODE (base) == VALUE
-		  && canon_value_cmp (base, loc)))
+	  /* Consolidate plus_constants.  */
+	  while (ofst && GET_CODE (loc) == PLUS
+		 && GET_CODE (XEXP (loc, 1)) == CONST_INT)
 	    {
-	      loc = l->loc;
-	      break;
+	      ofst += INTVAL (XEXP (loc, 1));
+	      loc = XEXP (loc, 0);
 	    }
-	}
 
-      /* No luck with the dataflow set, so we're done.  */
-      if (!l)
-	break;
+	  retry = false;
+	}
+      else
+	{
+	  x = canon_rtx (loc);
+	  if (retry)
+	    retry = (x != loc);
+	  loc = x;
+	}
     }
 
   /* Add OFST back in.  */
@@ -2052,19 +2168,6 @@  vt_canonicalize_addr (dataflow_set *set, rtx oloc)
   return loc;
 }
 
-/* Return true iff ADDR has a stack register as the base address.  */
-
-static inline bool
-vt_stack_offset_p (rtx addr)
-{
-  rtx base = vt_get_canonicalize_base (addr);
-
-  if (GET_CODE (base) != REG)
-    return false;
-
-  return REGNO_PTR_FRAME_P (REGNO (base));
-}
-
 /* Return true iff there's a true dependence between MLOC and LOC.
    MADDR must be a canonicalized version of MLOC's address.  */
 
@@ -2074,15 +2177,10 @@  vt_canon_true_dep (dataflow_set *set, rtx mloc, rtx maddr, rtx loc)
   if (GET_CODE (loc) != MEM)
     return false;
 
-  if (!canon_true_dependence (mloc, GET_MODE (mloc), maddr, loc, NULL))
+  rtx addr = vt_canonicalize_addr (set, XEXP (loc, 0));
+  if (!canon_true_dependence (mloc, GET_MODE (mloc), maddr, loc, addr))
     return false;
 
-  if (!MEM_EXPR (loc) && vt_stack_offset_p (maddr))
-    {
-      rtx addr = vt_canonicalize_addr (set, XEXP (loc, 0));
-      return canon_true_dependence (mloc, GET_MODE (mloc), maddr, loc, addr);
-    }
-
   return true;
 }
 
@@ -2177,6 +2275,8 @@  clobber_overlapping_mems (dataflow_set *set, rtx loc)
 {
   struct overlapping_mems coms;
 
+  gcc_checking_assert (GET_CODE (loc) == MEM);
+
   coms.set = set;
   coms.loc = canon_rtx (loc);
   coms.addr = vt_canonicalize_addr (set, XEXP (loc, 0));
@@ -2358,6 +2458,17 @@  val_store (dataflow_set *set, rtx val, rtx loc, rtx insn, bool modified)
   val_bind (set, val, loc, modified);
 }
 
+/* Clear (canonical address) slots that reference X.  */
+
+static bool
+local_get_addr_clear_given_value (const void *v ATTRIBUTE_UNUSED,
+				  void **slot, void *x)
+{
+  if (vt_get_canonicalize_base ((rtx)*slot) == x)
+    *slot = NULL;
+  return true;
+}
+
 /* Reset this node, detaching all its equivalences.  Return the slot
    in the variable hash table that holds dv, if there is one.  */
 
@@ -2373,6 +2484,28 @@  val_reset (dataflow_set *set, decl_or_value dv)
 
   gcc_assert (var->n_var_parts == 1);
 
+  if (var->onepart == ONEPART_VALUE)
+    {
+      rtx x = dv_as_value (dv);
+      void **slot;
+      
+      /* Relationships in the global cache don't change, so reset the
+	 local cache entry only.  */
+      slot = pointer_map_contains (local_get_addr_cache, x);
+      if (slot)
+	{
+	  /* If the value resolved back to itself, odds are that other
+	     values may have cached it too.  These entries now refer
+	     to the old X, so detach them too.  Entries that used the
+	     old X but resolved to something else remain ok as long as
+	     that something else isn't also reset.  */
+	  if (*slot == x)
+	    pointer_map_traverse (local_get_addr_cache,
+				  local_get_addr_clear_given_value, x);
+	  *slot = NULL;
+	}
+    }
+
   cval = NULL;
   for (node = var->var_part[0].loc_chain; node; node = node->next)
     if (GET_CODE (node->loc) == VALUE
@@ -6424,6 +6557,9 @@  compute_bb_dataflow (basic_block bb)
   dataflow_set_copy (&old_out, out);
   dataflow_set_copy (out, in);
 
+  if (MAY_HAVE_DEBUG_INSNS)
+    local_get_addr_cache = pointer_map_create ();
+
   FOR_EACH_VEC_ELT (VTI (bb)->mos, i, mo)
     {
       rtx insn = mo->insn;
@@ -6613,7 +6749,12 @@  compute_bb_dataflow (basic_block bb)
 	      else if (REG_P (uloc))
 		var_regno_delete (out, REGNO (uloc));
 	      else if (MEM_P (uloc))
-		clobber_overlapping_mems (out, uloc);
+		{
+		  gcc_checking_assert (GET_CODE (vloc) == MEM);
+		  gcc_checking_assert (dstv == vloc);
+		  if (dstv != vloc)
+		    clobber_overlapping_mems (out, vloc);
+		}
 
 	      val_store (out, val, dstv, insn, true);
 	    }
@@ -6700,6 +6841,9 @@  compute_bb_dataflow (basic_block bb)
 
   if (MAY_HAVE_DEBUG_INSNS)
     {
+      pointer_map_destroy (local_get_addr_cache);
+      local_get_addr_cache = NULL;
+
       dataflow_set_equiv_regs (out);
       htab_traverse (shared_hash_htab (out->vars), canonicalize_values_mark,
 		     out);
@@ -9113,7 +9257,12 @@  emit_notes_in_bb (basic_block bb, dataflow_set *set)
 	      else if (REG_P (uloc))
 		var_regno_delete (set, REGNO (uloc));
 	      else if (MEM_P (uloc))
-		clobber_overlapping_mems (set, uloc);
+		{
+		  gcc_checking_assert (GET_CODE (vloc) == MEM);
+		  gcc_checking_assert (vloc == dstv);
+		  if (vloc != dstv)
+		    clobber_overlapping_mems (set, vloc);
+		}
 
 	      val_store (set, val, dstv, insn, true);
 
@@ -9240,9 +9389,16 @@  vt_emit_notes (void)
 	 subsequent basic blocks.  */
       emit_notes_for_differences (BB_HEAD (bb), &cur, &VTI (bb)->in);
 
+      if (MAY_HAVE_DEBUG_INSNS)
+	local_get_addr_cache = pointer_map_create ();
+
       /* Emit the notes for the changes in the basic block itself.  */
       emit_notes_in_bb (bb, &cur);
 
+      if (MAY_HAVE_DEBUG_INSNS)
+	pointer_map_destroy (local_get_addr_cache);
+      local_get_addr_cache = NULL;
+
       /* Free memory occupied by the in hash table, we won't need it
 	 again.  */
       dataflow_set_clear (&VTI (bb)->in);
@@ -9611,11 +9767,13 @@  vt_initialize (void)
       valvar_pool = create_alloc_pool ("small variable_def pool",
 				       sizeof (struct variable_def), 256);
       preserved_values.create (256);
+      global_get_addr_cache = pointer_map_create ();
     }
   else
     {
       scratch_regs = NULL;
       valvar_pool = NULL;
+      global_get_addr_cache = NULL;
     }
 
   if (MAY_HAVE_DEBUG_INSNS)
@@ -9952,6 +10110,9 @@  vt_finalize (void)
 
   if (MAY_HAVE_DEBUG_INSNS)
     {
+      if (global_get_addr_cache)
+	pointer_map_destroy (global_get_addr_cache);
+      global_get_addr_cache = NULL;
       if (loc_exp_dep_pool)
 	free_alloc_pool (loc_exp_dep_pool);
       loc_exp_dep_pool = NULL;