[PATCH] ranger: Fix up fold_using_range::range_of_address [PR103255]

Jakub Jelinek jakub@redhat.com
Wed Nov 17 09:32:00 GMT 2021


Hi!

If on &base->member the offset isn't constant or isn't zero and
-fdelete-null-pointer-checks and not -fwrapv-pointer and base has a range
that doesn't include NULL, we return the range of the base.
Usually it isn't a big deal, because for most pointers we just use
varying, range_zero and range_nonzero ranges and nothing beyond that,
but if a pointer is initialized from a constant, we actually track the
exact range and in that case this causes miscompilation.
As discussed on IRC, I think doing something like:
	      offset_int off2;
	      if (off_cst && off.is_constant (&off2))
		{
		  tree cst = wide_int_to_tree (sizetype, off2 / BITS_PER_UNIT);
		  // adjust range r with POINTER_PLUS_EXPR cst
		  if (!range_includes_zero_p (&r))
		    return true;
		}
	      // Fallback
	      r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt)));
	      return true;
could work, given that most of the pointer ranges are just the simple ones
perhaps it is too much for little benefit.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2021-11-17  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/103255
	* gimple-range-fold.cc (fold_using_range::range_of_address): Return
	range_nonzero rather than unadjusted base's range.  Formatting fixes.

	* gcc.c-torture/execute/pr103255.c: New test.

--- gcc/gimple-range-fold.cc.jj	2021-11-04 12:27:02.341298923 +0100
+++ gcc/gimple-range-fold.cc	2021-11-16 22:10:44.453974329 +0100
@@ -720,14 +720,20 @@ fold_using_range::range_of_address (iran
 	}
       /* If &X->a is equal to X, the range of X is the result.  */
       if (off_cst && known_eq (off, 0))
-	  return true;
+	return true;
       else if (flag_delete_null_pointer_checks
 	       && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (expr)))
 	{
-	 /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't
-	 allow going from non-NULL pointer to NULL.  */
-	   if(!range_includes_zero_p (&r))
-	    return true;
+	  /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't
+	     allow going from non-NULL pointer to NULL.  */
+	  if (!range_includes_zero_p (&r))
+	    {
+	      /* We could here instead adjust r by off >> LOG2_BITS_PER_UNIT
+		 using POINTER_PLUS_EXPR if off_cst and just fall back to
+		 this.  */
+	      r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt)));
+	      return true;
+	    }
 	}
       /* If MEM_REF has a "positive" offset, consider it non-NULL
 	 always, for -fdelete-null-pointer-checks also "negative"
--- gcc/testsuite/gcc.c-torture/execute/pr103255.c.jj	2021-11-16 22:14:10.660118225 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr103255.c	2021-11-16 22:13:56.506314265 +0100
@@ -0,0 +1,41 @@
+/* PR tree-optimization/103255 */
+
+struct H
+{
+  unsigned a;
+  unsigned b;
+  unsigned c;
+};
+
+#if __SIZEOF_POINTER__ >= 4
+#define ADDR 0x400000
+#else
+#define ADDR 0x4000
+#endif
+#define OFF 0x20
+
+int
+main ()
+{
+  struct H *h = 0;
+  unsigned long o;
+  volatile int t = 1;
+
+  for (o = OFF; o <= OFF; o += 0x1000)
+    {
+      struct H *u;
+      u = (struct H *) (ADDR + o);
+      if (t)
+	{
+	  h = u;
+	  break;
+	}
+    }
+
+  if (h == 0)
+    return 0;
+  unsigned *tt = &h->b;
+  if ((__SIZE_TYPE__) tt != (ADDR + OFF + __builtin_offsetof (struct H, b)))
+    __builtin_abort ();
+  return 0;
+}

	Jakub



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