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Re: Optimize callers using nonnull attribute


On Mon, 7 Oct 2013, Richard Biener wrote:

On Mon, Oct 7, 2013 at 12:33 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
Hello,

this patch asserts that when we call a function with the nonnull attribute,
the corresponding argument is not zero, just like when we dereference a
pointer. Everything is under a check for flag_delete_null_pointer_checks.

Note that this function currently gives up if the statement may throw
(because in some languages indirections may throw?), but this could probably
be relaxed a bit so my example would still work when compiled with g++,
without having to mark f1 and f2 as throw().

Bootstrap (default languages) + testsuite on x86_64-unknown-linux-gnu.

Can you please restructure it in a way to not require a goto?  That is,
move searching for a non-null opportunity into a helper function?

Thanks. I wasn't sure what to put in the helper and what to keep in the original function, so I'll wait a bit for comments before the commit.

Bootstrap (default languages) + testsuite on x86_64-unknown-linux-gnu.

2013-10-08  Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/58480
gcc/
	* tree-vrp.c (infer_nonnull_range): New function.
	(infer_value_range): Call infer_nonnull_range.

gcc/testsuite/
	* gcc.dg/tree-ssa/pr58480.c: New file.

--
Marc Glisse
Index: testsuite/gcc.dg/tree-ssa/pr58480.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/pr58480.c	(revision 0)
+++ testsuite/gcc.dg/tree-ssa/pr58480.c	(working copy)
@@ -0,0 +1,19 @@
+/* { dg-do compile { target { ! keeps_null_pointer_checks } } } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+extern void eliminate (void);
+extern void* f1 (void *a, void *b) __attribute__((nonnull));
+extern void* f2 (void *a, void *b) __attribute__((nonnull(2)));
+void g1 (void*p, void*q){
+  f1 (q, p);
+  if (p == 0)
+    eliminate ();
+}
+void g2 (void*p, void*q){
+  f2 (q, p);
+  if (p == 0)
+    eliminate ();
+}
+
+/* { dg-final { scan-tree-dump-times "Folding predicate\[^\\n\]*to 0" 2 "vrp1" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */

Property changes on: testsuite/gcc.dg/tree-ssa/pr58480.c
___________________________________________________________________
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Added: svn:keywords
## -0,0 +1 ##
+Author Date Id Revision URL
\ No newline at end of property
Index: tree-vrp.c
===================================================================
--- tree-vrp.c	(revision 203241)
+++ tree-vrp.c	(working copy)
@@ -4455,63 +4455,103 @@ build_assert_expr_for (tree cond, tree v
 
 static inline bool
 fp_predicate (gimple stmt)
 {
   GIMPLE_CHECK (stmt, GIMPLE_COND);
 
   return FLOAT_TYPE_P (TREE_TYPE (gimple_cond_lhs (stmt)));
 }
 
 
+/* If OP can be inferred to be non-zero after STMT executes, return true.  */
+
+static bool
+infer_nonnull_range (gimple stmt, tree op)
+{
+  /* We can only assume that a pointer dereference will yield
+     non-NULL if -fdelete-null-pointer-checks is enabled.  */
+  if (!flag_delete_null_pointer_checks
+      || !POINTER_TYPE_P (TREE_TYPE (op))
+      || gimple_code (stmt) == GIMPLE_ASM)
+    return false;
+
+  unsigned num_uses, num_loads, num_stores;
+
+  count_uses_and_derefs (op, stmt, &num_uses, &num_loads, &num_stores);
+  if (num_loads + num_stores > 0)
+    return true;
+
+  if (gimple_code (stmt) == GIMPLE_CALL)
+    {
+      tree fntype = gimple_call_fntype (stmt);
+      tree attrs = TYPE_ATTRIBUTES (fntype);
+      for (; attrs; attrs = TREE_CHAIN (attrs))
+	{
+	  attrs = lookup_attribute ("nonnull", attrs);
+
+	  /* If "nonnull" wasn't specified, we know nothing about
+	     the argument.  */
+	  if (attrs == NULL_TREE)
+	    return false;
+
+	  /* If "nonnull" applies to all the arguments, then ARG
+	     is non-null.  */
+	  if (TREE_VALUE (attrs) == NULL_TREE)
+	    return true;
+
+	  /* Now see if op appears in the nonnull list.  */
+	  for (tree t = TREE_VALUE (attrs); t; t = TREE_CHAIN (t))
+	    {
+	      int idx = TREE_INT_CST_LOW (TREE_VALUE (t)) - 1;
+	      tree arg = gimple_call_arg (stmt, idx);
+	      if (op == arg)
+		return true;
+	    }
+	}
+    }
+
+  return false;
+}
+
 /* If the range of values taken by OP can be inferred after STMT executes,
    return the comparison code (COMP_CODE_P) and value (VAL_P) that
    describes the inferred range.  Return true if a range could be
    inferred.  */
 
 static bool
 infer_value_range (gimple stmt, tree op, enum tree_code *comp_code_p, tree *val_p)
 {
   *val_p = NULL_TREE;
   *comp_code_p = ERROR_MARK;
 
   /* Do not attempt to infer anything in names that flow through
      abnormal edges.  */
   if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op))
     return false;
 
   /* Similarly, don't infer anything from statements that may throw
-     exceptions.  */
+     exceptions. ??? Relax this requirement?  */
   if (stmt_could_throw_p (stmt))
     return false;
 
   /* If STMT is the last statement of a basic block with no
      successors, there is no point inferring anything about any of its
      operands.  We would not be able to find a proper insertion point
      for the assertion, anyway.  */
   if (stmt_ends_bb_p (stmt) && EDGE_COUNT (gimple_bb (stmt)->succs) == 0)
     return false;
 
-  /* We can only assume that a pointer dereference will yield
-     non-NULL if -fdelete-null-pointer-checks is enabled.  */
-  if (flag_delete_null_pointer_checks
-      && POINTER_TYPE_P (TREE_TYPE (op))
-      && gimple_code (stmt) != GIMPLE_ASM)
+  if (infer_nonnull_range (stmt, op))
     {
-      unsigned num_uses, num_loads, num_stores;
-
-      count_uses_and_derefs (op, stmt, &num_uses, &num_loads, &num_stores);
-      if (num_loads + num_stores > 0)
-	{
-	  *val_p = build_int_cst (TREE_TYPE (op), 0);
-	  *comp_code_p = NE_EXPR;
-	  return true;
-	}
+      *val_p = build_int_cst (TREE_TYPE (op), 0);
+      *comp_code_p = NE_EXPR;
+      return true;
     }
 
   return false;
 }
 
 
 void dump_asserts_for (FILE *, tree);
 void debug_asserts_for (tree);
 void dump_all_asserts (FILE *);
 void debug_all_asserts (void);

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