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* [PATCH] Teach VRP about x >> cst even if x is VARYING (PR tree-optimization/64322)
@ 2014-12-16 16:38 Jakub Jelinek
  2014-12-16 18:28 ` Richard Biener
  0 siblings, 1 reply; 2+ messages in thread
From: Jakub Jelinek @ 2014-12-16 16:38 UTC (permalink / raw)
  To: Richard Biener; +Cc: gcc-patches

Hi!

If for RSHIFT_EXPR vr0 is not VR_RANGE or is symbolic, currently we make
the result VARYING, even when we can do much better just by trying to
shift the min and max values down.
Divisions/modulo already handles it similarly, and +/-/& also handle it.

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

2014-12-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/64322
	* tree-vrp.c (extract_range_from_binary_expr_1): Attempt to derive
	range for RSHIFT_EXPR even if vr0 range is not VR_RANGE or is symbolic.

	* gcc.dg/tree-ssa/vrp95.c: New test.

--- gcc/tree-vrp.c.jj	2014-12-01 14:57:30.000000000 +0100
+++ gcc/tree-vrp.c	2014-12-16 10:17:27.543111649 +0100
@@ -2434,6 +2434,7 @@ extract_range_from_binary_expr_1 (value_
       && code != MAX_EXPR
       && code != PLUS_EXPR
       && code != MINUS_EXPR
+      && code != RSHIFT_EXPR
       && (vr0.type == VR_VARYING
 	  || vr1.type == VR_VARYING
 	  || vr0.type != vr1.type
@@ -2948,6 +2949,15 @@ extract_range_from_binary_expr_1 (value_
 	{
 	  if (code == RSHIFT_EXPR)
 	    {
+	      /* Even if vr0 is VARYING or otherwise not usable, we can derive
+		 useful ranges just from the shift count.  E.g.
+		 x >> 63 for signed 64-bit x is always [-1, 0].  */
+	      if (vr0.type != VR_RANGE || symbolic_range_p (&vr0))
+		{
+		  vr0.type = type = VR_RANGE;
+		  vr0.min = vrp_val_min (expr_type);
+		  vr0.max = vrp_val_max (expr_type);
+		}
 	      extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
 	      return;
 	    }
--- gcc/testsuite/gcc.dg/tree-ssa/vrp95.c.jj	2014-12-16 12:11:19.048361844 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp95.c	2014-12-16 12:24:47.080308362 +0100
@@ -0,0 +1,50 @@
+/* PR tree-optimization/64322 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+extern void link_error ();
+extern void required_check ();
+
+long long int
+foo (long long int x)
+{
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1;
+  if (x != 0 && x != -1)
+    link_error ();
+  return x;
+}
+
+unsigned long long int
+bar (unsigned long long int x)
+{
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1;
+  if (x != 0 && x != 1)
+    link_error ();
+  return x;
+}
+
+long long int
+baz (long long int x)
+{
+  x = (x >> sizeof (long long int) * __CHAR_BIT__ - 1) << 1;
+  x = x / 0x100000000LL;
+  if (x != 0)
+    link_error ();
+  return x;
+}
+
+unsigned long long int
+range (unsigned long long int x, int y)
+{
+  y &= 3;
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1 - y;
+  if (x > 15)
+    link_error ();
+  if (x == 15)
+    required_check ();
+  return x;
+}
+
+/* { dg-final { scan-tree-dump-not "link_error" "vrp1" } } */
+/* { dg-final { scan-tree-dump "required_check" "vrp1" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */

	Jakub

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2014-12-16 16:38 [PATCH] Teach VRP about x >> cst even if x is VARYING (PR tree-optimization/64322) Jakub Jelinek
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