diff mbox series

match: Simplify `1 >> x` into `x == 0` [PR102705]

Message ID 20250115214117.2280291-1-quic_apinski@quicinc.com
State Committed
Commit 903ab914dd48c3131ded0cf427da50c23168024c
Headers
Series match: Simplify `1 >> x` into `x == 0` [PR102705] |

Checks

Context Check Description
linaro-tcwg-bot/tcwg_gcc_build--master-arm fail Patch failed to apply
linaro-tcwg-bot/tcwg_gcc_build--master-aarch64 fail Patch failed to apply

Commit Message

Andrew Pinski Jan. 15, 2025, 9:41 p.m. UTC 
  This in this PR we have missed optimization where we miss that,
`1 >> x` and `(1 >> x) ^ 1` can't be equal. There are a few ways of
optimizing this, the easiest and simpliest is to simplify `1 >> x` into
just `x == 0` as those are equivalant (if we ignore out of range values for x).
we already have an optimization for `(1 >> X) !=/== 0` so the only difference
here is we don't need the `!=/== 0` part to do the transformation.

So this removes the `(1 >> X) !=/== 0` transformation and just adds a simplfied
`1 >> x` -> `x == 0` one.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/102705

gcc/ChangeLog:

	* match.pd (`(1 >> X) != 0`): Remove pattern.
	(`1 >> x`): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr105832-2.c: Update testcase.
	* gcc.dg/tree-ssa/pr96669-1.c: Likewise.
	* gcc.dg/tree-ssa/pr102705-1.c: New test.
	* gcc.dg/tree-ssa/pr102705-2.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
---
 gcc/match.pd                               | 16 ++++++++--------
 gcc/testsuite/gcc.dg/tree-ssa/pr102705-1.c | 17 +++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr102705-2.c | 17 +++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr105832-2.c |  8 ++++----
 gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c  |  2 +-
 5 files changed, 47 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr102705-1.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr102705-2.c

Comments

Jeffrey Law Jan. 15, 2025, 11:01 p.m. UTC | #1 
On 1/15/25 2:41 PM, Andrew Pinski wrote:
> This in this PR we have missed optimization where we miss that,
> `1 >> x` and `(1 >> x) ^ 1` can't be equal. There are a few ways of
> optimizing this, the easiest and simpliest is to simplify `1 >> x` into
> just `x == 0` as those are equivalant (if we ignore out of range values for x).
> we already have an optimization for `(1 >> X) !=/== 0` so the only difference
> here is we don't need the `!=/== 0` part to do the transformation.
> 
> So this removes the `(1 >> X) !=/== 0` transformation and just adds a simplfied
> `1 >> x` -> `x == 0` one.
> 
> Bootstrapped and tested on x86_64-linux-gnu.
> 
> 	PR tree-optimization/102705
> 
> gcc/ChangeLog:
> 
> 	* match.pd (`(1 >> X) != 0`): Remove pattern.
> 	(`1 >> x`): New pattern.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.dg/tree-ssa/pr105832-2.c: Update testcase.
> 	* gcc.dg/tree-ssa/pr96669-1.c: Likewise.
> 	* gcc.dg/tree-ssa/pr102705-1.c: New test.
> 	* gcc.dg/tree-ssa/pr102705-2.c: New test.
OK
jeff
diff mbox series

Patch

diff --git a/gcc/match.pd b/gcc/match.pd
index 17193087498..b6cbb851897 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4998,6 +4998,11 @@  DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
         (op @0 { build_int_cst (TREE_TYPE (@1), prec - 1); })))
       (op @0 { build_int_cst (TREE_TYPE (@1), low); })))))))
 
+/* Fold `1 >> a` into `a == 0` for scalar integral types. */
+(simplify
+ (rshift integer_onep @2)
+ (if (INTEGRAL_TYPE_P (type))
+  (convert (eq:boolean_type_node @2 { build_zero_cst (TREE_TYPE (@2)); }))))
 
 /* Simplify (CST << x) & 1 to 0 if CST is even or to x == 0 if it is odd.  */
 (simplify
@@ -5009,7 +5014,8 @@  DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 /* Simplify ((C << x) & D) != 0 where C and D are power of two constants,
    either to false if D is smaller (unsigned comparison) than C, or to
    x == log2 (D) - log2 (C).  Similarly for right shifts.
-   Note for `(1 >> x)`, the & 1 has been removed so matching that seperately. */
+   Note `(1 >> x)`, the & 1 has been removed so but will have been
+   already folded above.  */
 (for cmp (ne eq)
      icmp (eq ne)
  (simplify
@@ -5026,13 +5032,7 @@  DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	    int c2 = wi::clz (wi::to_wide (@2)); }
      (if (c1 > c2)
       { constant_boolean_node (cmp == NE_EXPR ? false : true, type); }
-      (icmp @0 { build_int_cst (TREE_TYPE (@0), c2 - c1); })))))
- /* `(1 >> X) != 0` -> `X == 0` */
- /* `(1 >> X) == 0` -> `X != 0` */
- (simplify
-  (cmp (rshift integer_onep@1 @0) integer_zerop)
-   (if (INTEGRAL_TYPE_P (TREE_TYPE (@1)))
-    (icmp @0 { build_zero_cst (TREE_TYPE (@0)); }))))
+      (icmp @0 { build_int_cst (TREE_TYPE (@0), c2 - c1); }))))))
 
 /* (CST1 << A) == CST2 -> A == ctz (CST2) - ctz (CST1)
    (CST1 << A) != CST2 -> A != ctz (CST2) - ctz (CST1)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr102705-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr102705-1.c
new file mode 100644
index 00000000000..60b53c03472
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr102705-1.c
@@ -0,0 +1,17 @@ 
+/* PR tree-optimization/102705 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-original" } */
+/* { dg-final { scan-tree-dump "a == 0" "original" } } */
+/* { dg-final { scan-tree-dump "b == 0" "original" } } */
+
+int
+f1 (int a)
+{
+  return (1 >> a);
+}
+
+int
+f2 (int b)
+{
+  return ((1 >> b) & 1);
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr102705-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr102705-2.c
new file mode 100644
index 00000000000..a12606c7856
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr102705-2.c
@@ -0,0 +1,17 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* PR tree-optimization/102705 */
+/* { dg-final { scan-tree-dump-not "foo " "optimized" } } */
+
+
+void foo(void);
+static int b;
+static char c;
+static short a(short d, short e) { return e == 0 || d && e == 1 ? 0 : d % e; }
+int main() {
+  b = c = b >= 2 ? 0 : 1 >> b;
+  short f = a(0 >= 0 ^ c, 5);
+  if (f == c)
+    foo();
+  a(0, 9);
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105832-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105832-2.c
index 2d2a33e2755..ebcc76bda68 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr105832-2.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105832-2.c
@@ -1,10 +1,10 @@ 
 /* PR tree-optimization/105832 */
 /* { dg-do compile } */
 /* { dg-options "-O2 -fdump-tree-original" } */
-/* { dg-final { scan-tree-dump "return a == 0;" "original" } } */
-/* { dg-final { scan-tree-dump "return b == 0;" "original" } } */
-/* { dg-final { scan-tree-dump "return c != 0;" "original" } } */
-/* { dg-final { scan-tree-dump "return d != 0;" "original" } } */
+/* { dg-final { scan-tree-dump "a == 0" "original" } } */
+/* { dg-final { scan-tree-dump "b == 0" "original" } } */
+/* { dg-final { scan-tree-dump "c != 0" "original" } } */
+/* { dg-final { scan-tree-dump "d != 0" "original" } } */
 
 int
 f1 (int a)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c
index 6a95a6ba8c1..56932330218 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr96669-1.c
@@ -5,7 +5,7 @@ 
 /* { dg-final { scan-tree-dump "return 1;" "original" } } */
 /* { dg-final { scan-tree-dump "return c == 3;" "original" } } */
 /* { dg-final { scan-tree-dump "return d != 1;" "original" } } */
-/* { dg-final { scan-tree-dump "return e != 0;" "original" } } */
+/* { dg-final { scan-tree-dump "e != 0" "original" } } */
 /* { dg-final { scan-tree-dump "return f == 1;" "original" } } */
 /* { dg-final { scan-tree-dump "return 0;" "original" } } */
 /* { dg-final { scan-tree-dump "return h != 1;" "original" } } */