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

[Marek Polacek <polacek at redhat dot com>]

On Tue, Jun 09, 2015 at 09:53:21AM +0200, Richard Biener wrote:
> >> +/* (CST1 << A) == CST2 -> A == ctz (CST2) - ctz (CST1)
> >> +   (CST1 << A) != CST2 -> A != ctz (CST2) - ctz (CST1)
> >> +   if CST2 != 0.  */
> >> +(for cmp (ne eq)
> >> + (simplify
> >> +  (cmp (lshift INTEGER_CST@0 @1) INTEGER_CST@2)
> >> +  (with {
> >> +   unsigned int cand = wi::ctz (@2) - wi::ctz (@0); }
> >> +  (if (!integer_zerop (@2)
> >
> >
> > You can probably use directly wi::ne_p (@2, 0) here. Shouldn't this be
> > indented one space more?
> 
> Yes, one space more.  I suppose using integer_zerop might in theory
> allow for handling vector shifts at some point ...?
 
Fixed the formatting.  But I kept the integer_zerop.

> >> +       && wi::eq_p (wi::lshift (@0, cand), @2))
> >> +   (cmp @1 { build_int_cst (TREE_TYPE (@1), cand); })))))
> >
> >
> > Making 'cand' signed, you could return 0 when cand<0, like (2<<x)==1. You
> > could also return 0 when the candidate turns out not to work: (3<<x)==4.
> 
> Sounds like a good improvement.
 
Yeah, it makes sense to do that while I'm on this.  Done, and a new
test added.

> Otherwise the patch looks ok to me as well - mind doing the improvement above?

Thank you both.  How does this look now?

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

2015-06-09  Marek Polacek  <polacek@redhat.com>

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

	* gcc.dg/pr66299-1.c: New test.
	* gcc.dg/pr66299-2.c: New test.
	* gcc.dg/pr66299-3.c: New test.

diff --git gcc/match.pd gcc/match.pd
index abd7851..560b218 100644
--- gcc/match.pd
+++ gcc/match.pd
@@ -676,6 +676,21 @@ 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 == ctz (CST2) - ctz (CST1)
+   (CST1 << A) != CST2 -> A != ctz (CST2) - ctz (CST1)
+   if CST2 != 0.  */
+(for cmp (ne eq)
+ (simplify
+  (cmp (lshift INTEGER_CST@0 @1) INTEGER_CST@2)
+  (with { int cand = wi::ctz (@2) - wi::ctz (@0); }
+   (if (cand < 0
+	|| (!integer_zerop (@2)
+	    && wi::ne_p (wi::lshift (@0, cand), @2)))
+    { constant_boolean_node (cmp == NE_EXPR, type); })
+   (if (!integer_zerop (@2)
+	&& wi::eq_p (wi::lshift (@0, cand), @2))
+    (cmp @1 { build_int_cst (TREE_TYPE (@1), cand); })))))
+
 /* 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..e75146b 100644
--- gcc/testsuite/gcc.dg/pr66299-1.c
+++ gcc/testsuite/gcc.dg/pr66299-1.c
@@ -0,0 +1,92 @@
+/* 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 ();
+}
+
+void
+test5 (int x)
+{
+  if ((0 << x) == 1
+      || (0 << x) != 0
+      || (0x8001U << x) != 0x20000U)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  test1 (1);
+  test2 (2);
+  test3 (4U);
+  test4 (3U);
+  test5 (17);
+}
+
+/* { dg-final { scan-tree-dump-not "<<" "original" } } */
diff --git gcc/testsuite/gcc.dg/pr66299-2.c gcc/testsuite/gcc.dg/pr66299-2.c
index e69de29..45e9218 100644
--- gcc/testsuite/gcc.dg/pr66299-2.c
+++ gcc/testsuite/gcc.dg/pr66299-2.c
@@ -0,0 +1,33 @@
+/* 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" } } */
diff --git gcc/testsuite/gcc.dg/pr66299-3.c gcc/testsuite/gcc.dg/pr66299-3.c
index e69de29..ffee049 100644
--- gcc/testsuite/gcc.dg/pr66299-3.c
+++ gcc/testsuite/gcc.dg/pr66299-3.c
@@ -0,0 +1,68 @@
+/* PR tree-optimization/66299 */
+/* { dg-do run } */
+/* { dg-options "-fdump-tree-original" } */
+
+void __attribute__ ((noinline, noclone))
+test1 (int x)
+{
+  if ((2 << x) == 1
+      || (8 << x) == 1
+      || (8 << x) == 2
+      || (3072 << x) == 3
+      || (294912 << x) == 9
+      || (45056 << x) == 11
+      || (2176 << x) == 17)
+    __builtin_abort ();
+}
+
+void __attribute__ ((noinline, noclone))
+test2 (int x)
+{
+  if ((2 << x) != 1
+      && (8 << x) != 1
+      && (8 << x) != 2
+      && (3072 << x) != 3
+      && (294912 << x) != 9
+      && (45056 << x) != 11
+      && (2176 << x) != 17)
+    ;
+  else
+    __builtin_abort ();
+}
+
+void __attribute__ ((noinline, noclone))
+test3 (int x)
+{
+  if ((3 << x) == 4
+      || (1 << x) == 12
+      || (40 << x) == 1024
+      || (2 << x) == 84
+      || (3 << x) == 16384
+      || (10 << x) == 6144)
+    __builtin_abort ();
+}
+
+void __attribute__ ((noinline, noclone))
+test4 (int x)
+{
+  if ((3 << x) != 4
+      && (1 << x) != 12
+      && (40 << x) != 1024
+      && (2 << x) != 84
+      && (3 << x) != 16384
+      && (10 << x) != 6144)
+    ;
+  else
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  test1 (0);
+  test2 (1);
+  test3 (1);
+  test4 (2);
+}
+
+/* { dg-final { scan-tree-dump-not "(<<|==|!=)" "original" } } */

	Marek