[PATCH] Optimize (CST1 << A) == CST2 (PR tree-optimization/66299)

[Marek Polacek <polacek at redhat dot com>]

This PR points out that we weren't able to optimize 1 << x == 2 to just
x == 1.  This is my attempt to fix that: if we see (CST1 << A) == CST2
and CST2 is a multiple of CST1, use log2 to get rid of the shift, but
only if the result of the shift is a natural number (including zero).

If CST2 is not a multiple of CST1, then the whole expression can be
discarded, but I'd like to do that as a follow-up.
(It would help if our current match.pd grammar allowed us to use "else",
any plans on doing that?)

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

2015-05-28  Marek Polacek  <polacek@redhat.com>

	PR tree-optimization/66299
	* match.pd ((CST1 << A) == CST2 -> A == log2 (CST2 / CST1),
	(CST1 << A) != CST2 -> A != log2 (CST2 / CST1)): New
	patterns.

	* gcc.dg/pr66299-1.c: New test.
	* gcc.dg/pr66299-2.c: New test.

diff --git gcc/match.pd gcc/match.pd
index abd7851..5d07a70 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -676,6 +676,19 @@ along with GCC; see the file COPYING3.  If not see
   (cmp (bit_and (lshift integer_onep @0) integer_onep) integer_zerop)
   (icmp @0 { build_zero_cst (TREE_TYPE (@0)); })))
 
+/* (CST1 << A) == CST2 -> A == log2 (CST2 / CST1)
+   (CST1 << A) != CST2 -> A != log2 (CST2 / CST1)
+   if CST2 is a multiple of CST1.  */
+(for cmp (ne eq)
+ (simplify
+  (cmp (lshift@3 INTEGER_CST@0 @1) INTEGER_CST@2)
+  (if ((TREE_CODE (@3) != SSA_NAME || has_single_use (@3))
+       && wi::multiple_of_p (@2, @0, TYPE_SIGN (type)))
+   (with {
+    int shift = wi::exact_log2 (wi::div_trunc (@2, @0, TYPE_SIGN (type))); }
+   (if (shift != -1)
+    (cmp @1 { build_int_cst (TREE_TYPE (@1), shift); }))))))
+
 /* Simplifications of conversions.  */
 
 /* Basic strip-useless-type-conversions / strip_nops.  */
diff --git gcc/testsuite/gcc.dg/pr66299-1.c gcc/testsuite/gcc.dg/pr66299-1.c
index e69de29..9d41275 100644
--- gcc/testsuite/gcc.dg/pr66299-1.c
+++ gcc/testsuite/gcc.dg/pr66299-1.c
@@ -0,0 +1,83 @@
+/* PR tree-optimization/66299 */
+/* { dg-do run } */
+/* { dg-options "-fdump-tree-original" } */
+
+void
+test1 (int x)
+{
+  if ((0 << x) != 0
+      || (1 << x) != 2
+      || (2 << x) != 4
+      || (3 << x) != 6
+      || (4 << x) != 8
+      || (5 << x) != 10
+      || (6 << x) != 12
+      || (7 << x) != 14
+      || (8 << x) != 16
+      || (9 << x) != 18
+      || (10 << x) != 20)
+    __builtin_abort ();
+}
+
+void
+test2 (int x)
+{
+  if (!((0 << x) == 0
+        && (1 << x) == 4
+        && (2 << x) == 8
+        && (3 << x) == 12
+        && (4 << x) == 16
+        && (5 << x) == 20
+        && (6 << x) == 24
+        && (7 << x) == 28
+        && (8 << x) == 32
+        && (9 << x) == 36
+	&& (10 << x) == 40))
+    __builtin_abort ();
+}
+
+void
+test3 (unsigned int x)
+{
+  if ((0U << x) != 0U
+      || (1U << x) != 16U
+      || (2U << x) != 32U
+      || (3U << x) != 48U
+      || (4U << x) != 64U
+      || (5U << x) != 80U
+      || (6U << x) != 96U
+      || (7U << x) != 112U
+      || (8U << x) != 128U
+      || (9U << x) != 144U
+      || (10U << x) != 160U)
+    __builtin_abort ();
+}
+
+void
+test4 (unsigned int x)
+{
+  if (!((0U << x) == 0U
+	|| (1U << x) == 8U
+	|| (2U << x) == 16U
+	|| (3U << x) == 24U
+	|| (4U << x) == 32U
+	|| (5U << x) == 40U
+	|| (6U << x) == 48U
+	|| (7U << x) == 56U
+	|| (8U << x) == 64U
+	|| (9U << x) == 72U
+	|| (10U << x) == 80U))
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  test1 (1);
+  test2 (2);
+  test3 (4U);
+  test4 (3U);
+}
+
+/* { dg-final { scan-tree-dump-not "<<" "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */
diff --git gcc/testsuite/gcc.dg/pr66299-2.c gcc/testsuite/gcc.dg/pr66299-2.c
index e69de29..dde0549 100644
--- gcc/testsuite/gcc.dg/pr66299-2.c
+++ gcc/testsuite/gcc.dg/pr66299-2.c
@@ -0,0 +1,34 @@
+/* PR tree-optimization/66299 */
+/* { dg-do run } */
+/* { dg-options "-fdump-tree-optimized -O" } */
+
+void
+test1 (int x, unsigned u)
+{
+  if ((1U << x) != 64
+      || (2 << x) != u
+      || (x << x) != 384
+      || (3 << x) == 9
+      || (x << 14) != 98304U
+      || (1 << x) == 14
+      || (3 << 2) != 12)
+    __builtin_abort ();
+}
+
+void
+test2 (int x)
+{
+  unsigned int t = ((unsigned int) 1U << x);
+  if (t != 2U)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  test1 (6, 128U);
+  test2 (1);
+}
+
+/* { dg-final { scan-tree-dump-not "<<" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */

	Marek