c++, tree: optimize walk_tree_1 and cp_walk_subtrees

These functions currently repeatedly dereference tp during the subtree
walks, dereferences which the compiler can't CSE because it can't
guarantee that the subtree walking doesn't modify *tp.

But we already implicitly require that TREE_CODE (*tp) remains the same
throughout the subtree walks, so it doesn't seem to be a huge leap to
strengthen that to requiring *tp remains the same.

So this patch manually CSEs the dereferences of *tp.  This means that a
callback function can no longer replace *tp with another tree (of the
same TREE_CODE) when walking one of its subtrees, but that doesn't sound
like a useful capability anyway.

gcc/cp/ChangeLog:

	* tree.cc (cp_walk_subtrees): Avoid repeatedly dereferencing tp.
	<case DECLTYPE_TYPE>: Use cp_unevaluated and WALK_SUBTREE.
	<case ALIGNOF_EXPR etc>: Likewise.

gcc/ChangeLog:

	* tree.cc (walk_tree_1): Avoid repeatedly dereferencing tp
	and type_p.

1 files changed, 51 insertions, 52 deletions

diff --git a/gcc/tree.cc b/gcc/tree.cc
index 207293c..5f2af07 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -11300,10 +11300,6 @@ tree
 walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	     hash_set<tree> *pset, walk_tree_lh lh)
 {
-  enum tree_code code;
-  int walk_subtrees;
-  tree result;
-
 #define WALK_SUBTREE_TAIL(NODE)				\
   do							\
     {							\
@@ -11323,14 +11319,15 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
     return NULL_TREE;
 
   /* Call the function.  */
-  walk_subtrees = 1;
-  result = (*func) (tp, &walk_subtrees, data);
+  int walk_subtrees = 1;
+  tree result = (*func) (tp, &walk_subtrees, data);
 
   /* If we found something, return it.  */
   if (result)
     return result;
 
-  code = TREE_CODE (*tp);
+  tree t = *tp;
+  tree_code code = TREE_CODE (t);
 
   /* Even if we didn't, FUNC may have decided that there was nothing
      interesting below this point in the tree.  */
@@ -11338,9 +11335,9 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
     {
       /* But we still need to check our siblings.  */
       if (code == TREE_LIST)
-	WALK_SUBTREE_TAIL (TREE_CHAIN (*tp));
+	WALK_SUBTREE_TAIL (TREE_CHAIN (t));
       else if (code == OMP_CLAUSE)
-	WALK_SUBTREE_TAIL (OMP_CLAUSE_CHAIN (*tp));
+	WALK_SUBTREE_TAIL (OMP_CLAUSE_CHAIN (t));
       else
 	return NULL_TREE;
     }
@@ -11370,58 +11367,58 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
       break;
 
     case TREE_LIST:
-      WALK_SUBTREE (TREE_VALUE (*tp));
-      WALK_SUBTREE_TAIL (TREE_CHAIN (*tp));
+      WALK_SUBTREE (TREE_VALUE (t));
+      WALK_SUBTREE_TAIL (TREE_CHAIN (t));
 
     case TREE_VEC:
       {
-	int len = TREE_VEC_LENGTH (*tp);
+	int len = TREE_VEC_LENGTH (t);
 
 	if (len == 0)
 	  break;
 
 	/* Walk all elements but the last.  */
 	for (int i = 0; i < len - 1; ++i)
-	  WALK_SUBTREE (TREE_VEC_ELT (*tp, i));
+	  WALK_SUBTREE (TREE_VEC_ELT (t, i));
 
 	/* Now walk the last one as a tail call.  */
-	WALK_SUBTREE_TAIL (TREE_VEC_ELT (*tp, len - 1));
+	WALK_SUBTREE_TAIL (TREE_VEC_ELT (t, len - 1));
       }
 
     case VECTOR_CST:
       {
-	unsigned len = vector_cst_encoded_nelts (*tp);
+	unsigned len = vector_cst_encoded_nelts (t);
 	if (len == 0)
 	  break;
 	/* Walk all elements but the last.  */
 	for (unsigned i = 0; i < len - 1; ++i)
-	  WALK_SUBTREE (VECTOR_CST_ENCODED_ELT (*tp, i));
+	  WALK_SUBTREE (VECTOR_CST_ENCODED_ELT (t, i));
 	/* Now walk the last one as a tail call.  */
-	WALK_SUBTREE_TAIL (VECTOR_CST_ENCODED_ELT (*tp, len - 1));
+	WALK_SUBTREE_TAIL (VECTOR_CST_ENCODED_ELT (t, len - 1));
       }
 
     case COMPLEX_CST:
-      WALK_SUBTREE (TREE_REALPART (*tp));
-      WALK_SUBTREE_TAIL (TREE_IMAGPART (*tp));
+      WALK_SUBTREE (TREE_REALPART (t));
+      WALK_SUBTREE_TAIL (TREE_IMAGPART (t));
 
     case CONSTRUCTOR:
       {
 	unsigned HOST_WIDE_INT idx;
 	constructor_elt *ce;
 
-	for (idx = 0; vec_safe_iterate (CONSTRUCTOR_ELTS (*tp), idx, &ce);
+	for (idx = 0; vec_safe_iterate (CONSTRUCTOR_ELTS (t), idx, &ce);
 	     idx++)
 	  WALK_SUBTREE (ce->value);
       }
       break;
 
     case SAVE_EXPR:
-      WALK_SUBTREE_TAIL (TREE_OPERAND (*tp, 0));
+      WALK_SUBTREE_TAIL (TREE_OPERAND (t, 0));
 
     case BIND_EXPR:
       {
 	tree decl;
-	for (decl = BIND_EXPR_VARS (*tp); decl; decl = DECL_CHAIN (decl))
+	for (decl = BIND_EXPR_VARS (t); decl; decl = DECL_CHAIN (decl))
 	  {
 	    /* Walk the DECL_INITIAL and DECL_SIZE.  We don't want to walk
 	       into declarations that are just mentioned, rather than
@@ -11432,23 +11429,23 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	    WALK_SUBTREE (DECL_SIZE (decl));
 	    WALK_SUBTREE (DECL_SIZE_UNIT (decl));
 	  }
-	WALK_SUBTREE_TAIL (BIND_EXPR_BODY (*tp));
+	WALK_SUBTREE_TAIL (BIND_EXPR_BODY (t));
       }
 
     case STATEMENT_LIST:
       {
 	tree_stmt_iterator i;
-	for (i = tsi_start (*tp); !tsi_end_p (i); tsi_next (&i))
+	for (i = tsi_start (t); !tsi_end_p (i); tsi_next (&i))
 	  WALK_SUBTREE (*tsi_stmt_ptr (i));
       }
       break;
 
     case OMP_CLAUSE:
       {
-	int len = omp_clause_num_ops[OMP_CLAUSE_CODE (*tp)];
+	int len = omp_clause_num_ops[OMP_CLAUSE_CODE (t)];
 	for (int i = 0; i < len; i++)
-	  WALK_SUBTREE (OMP_CLAUSE_OPERAND (*tp, i));
-	WALK_SUBTREE_TAIL (OMP_CLAUSE_CHAIN (*tp));
+	  WALK_SUBTREE (OMP_CLAUSE_OPERAND (t, i));
+	WALK_SUBTREE_TAIL (OMP_CLAUSE_CHAIN (t));
       }
 
     case TARGET_EXPR:
@@ -11457,10 +11454,10 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 
 	/* TARGET_EXPRs are peculiar: operands 1 and 3 can be the same.
 	   But, we only want to walk once.  */
-	len = (TREE_OPERAND (*tp, 3) == TREE_OPERAND (*tp, 1)) ? 2 : 3;
+	len = (TREE_OPERAND (t, 3) == TREE_OPERAND (t, 1)) ? 2 : 3;
 	for (i = 0; i < len; ++i)
-	  WALK_SUBTREE (TREE_OPERAND (*tp, i));
-	WALK_SUBTREE_TAIL (TREE_OPERAND (*tp, len));
+	  WALK_SUBTREE (TREE_OPERAND (t, i));
+	WALK_SUBTREE_TAIL (TREE_OPERAND (t, len));
       }
 
     case DECL_EXPR:
@@ -11475,15 +11472,15 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	 variable-sized types.
 
 	 Note that DECLs get walked as part of processing the BIND_EXPR.  */
-      if (TREE_CODE (DECL_EXPR_DECL (*tp)) == TYPE_DECL)
+      if (TREE_CODE (DECL_EXPR_DECL (t)) == TYPE_DECL)
 	{
 	  /* Call the function for the decl so e.g. copy_tree_body_r can
 	     replace it with the remapped one.  */
-	  result = (*func) (&DECL_EXPR_DECL (*tp), &walk_subtrees, data);
+	  result = (*func) (&DECL_EXPR_DECL (t), &walk_subtrees, data);
 	  if (result || !walk_subtrees)
 	    return result;
 
-	  tree *type_p = &TREE_TYPE (DECL_EXPR_DECL (*tp));
+	  tree *type_p = &TREE_TYPE (DECL_EXPR_DECL (t));
 	  if (TREE_CODE (*type_p) == ERROR_MARK)
 	    return NULL_TREE;
 
@@ -11494,21 +11491,23 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	  if (result || !walk_subtrees)
 	    return result;
 
+	  tree type = *type_p;
+
 	  /* But do not walk a pointed-to type since it may itself need to
 	     be walked in the declaration case if it isn't anonymous.  */
-	  if (!POINTER_TYPE_P (*type_p))
+	  if (!POINTER_TYPE_P (type))
 	    {
-	      result = walk_type_fields (*type_p, func, data, pset, lh);
+	      result = walk_type_fields (type, func, data, pset, lh);
 	      if (result)
 		return result;
 	    }
 
 	  /* If this is a record type, also walk the fields.  */
-	  if (RECORD_OR_UNION_TYPE_P (*type_p))
+	  if (RECORD_OR_UNION_TYPE_P (type))
 	    {
 	      tree field;
 
-	      for (field = TYPE_FIELDS (*type_p); field;
+	      for (field = TYPE_FIELDS (type); field;
 		   field = DECL_CHAIN (field))
 		{
 		  /* We'd like to look at the type of the field, but we can
@@ -11521,24 +11520,24 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 		  WALK_SUBTREE (DECL_FIELD_OFFSET (field));
 		  WALK_SUBTREE (DECL_SIZE (field));
 		  WALK_SUBTREE (DECL_SIZE_UNIT (field));
-		  if (TREE_CODE (*type_p) == QUAL_UNION_TYPE)
+		  if (TREE_CODE (type) == QUAL_UNION_TYPE)
 		    WALK_SUBTREE (DECL_QUALIFIER (field));
 		}
 	    }
 
 	  /* Same for scalar types.  */
-	  else if (TREE_CODE (*type_p) == BOOLEAN_TYPE
-		   || TREE_CODE (*type_p) == ENUMERAL_TYPE
-		   || TREE_CODE (*type_p) == INTEGER_TYPE
-		   || TREE_CODE (*type_p) == FIXED_POINT_TYPE
-		   || TREE_CODE (*type_p) == REAL_TYPE)
+	  else if (TREE_CODE (type) == BOOLEAN_TYPE
+		   || TREE_CODE (type) == ENUMERAL_TYPE
+		   || TREE_CODE (type) == INTEGER_TYPE
+		   || TREE_CODE (type) == FIXED_POINT_TYPE
+		   || TREE_CODE (type) == REAL_TYPE)
 	    {
-	      WALK_SUBTREE (TYPE_MIN_VALUE (*type_p));
-	      WALK_SUBTREE (TYPE_MAX_VALUE (*type_p));
+	      WALK_SUBTREE (TYPE_MIN_VALUE (type));
+	      WALK_SUBTREE (TYPE_MAX_VALUE (type));
 	    }
 
-	  WALK_SUBTREE (TYPE_SIZE (*type_p));
-	  WALK_SUBTREE_TAIL (TYPE_SIZE_UNIT (*type_p));
+	  WALK_SUBTREE (TYPE_SIZE (type));
+	  WALK_SUBTREE_TAIL (TYPE_SIZE_UNIT (type));
 	}
       /* FALLTHRU */
 
@@ -11548,20 +11547,20 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	  int i, len;
 
 	  /* Walk over all the sub-trees of this operand.  */
-	  len = TREE_OPERAND_LENGTH (*tp);
+	  len = TREE_OPERAND_LENGTH (t);
 
 	  /* Go through the subtrees.  We need to do this in forward order so
 	     that the scope of a FOR_EXPR is handled properly.  */
 	  if (len)
 	    {
 	      for (i = 0; i < len - 1; ++i)
-		WALK_SUBTREE (TREE_OPERAND (*tp, i));
-	      WALK_SUBTREE_TAIL (TREE_OPERAND (*tp, len - 1));
+		WALK_SUBTREE (TREE_OPERAND (t, i));
+	      WALK_SUBTREE_TAIL (TREE_OPERAND (t, len - 1));
 	    }
 	}
       /* If this is a type, walk the needed fields in the type.  */
-      else if (TYPE_P (*tp))
-	return walk_type_fields (*tp, func, data, pset, lh);
+      else if (TYPE_P (t))
+	return walk_type_fields (t, func, data, pset, lh);
       break;
     }