public inbox for gcc-patches@gcc.gnu.org
 help / color / mirror / Atom feed
* [COMMITTED] irange: keep better track of powers of 2.
@ 2022-09-27  8:46 Aldy Hernandez
  0 siblings, 0 replies; only message in thread
From: Aldy Hernandez @ 2022-09-27  8:46 UTC (permalink / raw)
  To: GCC patches; +Cc: Andrew MacLeod, drepper, Aldy Hernandez

When setting the nonzero bits to a mask containing only one bit, set
the range immediately, as it can be devined from the mask.  This helps
us keep better track of powers of two.

For example, with this patch a nonzero mask of 0x8000 is set to a
range of [0,0][0x8000,0x8000] with a nonzero mask of 0x8000.

Tested on x86-64 Linux.

p.s. Thanks for the bug report Uli.

gcc/ChangeLog:

	* value-range.cc (irange::set_nonzero_bits): Set range when known.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/popcount6.c: New test.
---
 gcc/testsuite/gcc.dg/tree-ssa/popcount6.c | 12 ++++++++++++
 gcc/value-range.cc                        | 13 +++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/popcount6.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount6.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount6.c
new file mode 100644
index 00000000000..1406ad9d33b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount6.c
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp" }
+
+int g(int n)
+{
+  n &= 0x8000;
+  if (n == 0)
+    return 1;
+  return __builtin_popcount(n);
+}
+
+// { dg-final { scan-tree-dump "return 1;" "evrp" } }
diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index 754379add19..6154d73ccf5 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -2930,6 +2930,19 @@ irange::set_nonzero_bits (const wide_int_ref &bits)
       set_nonzero_bits (NULL);
       return;
     }
+  // If we have only one bit set in the mask, we can figure out the
+  // range immediately.
+  if (wi::popcount (bits) == 1)
+    {
+      bool has_zero = contains_p (build_zero_cst (type ()));
+      set (type (), bits, bits);
+      if (has_zero)
+	{
+	  int_range<2> zero;
+	  zero.set_zero (type ());
+	  union_ (zero);
+	}
+    }
   set_nonzero_bits (wide_int_to_tree (type (), bits));
 }
 
-- 
2.37.1


^ permalink raw reply	[flat|nested] only message in thread

only message in thread, other threads:[~2022-09-27  8:46 UTC | newest]

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-27  8:46 [COMMITTED] irange: keep better track of powers of 2 Aldy Hernandez

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).