From be4a6551ed37c1e7dbdfb9400fc2e2b5d40c5be2 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Tue, 27 Sep 2022 08:05:30 +0200
Subject: [PATCH] irange: keep better track of powers of 2.

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.

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 000000000000..1406ad9d33b1
--- /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 754379add190..6154d73ccf5d 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));
 }
 
-- 
2.47.2