[gcc r13-2900] range-ops: Calculate the popcount of a singleton.

[Aldy Hernandez <aldyh@gcc.gnu.org>]

https://gcc.gnu.org/g:001c60ccfeaf9a480a56203418af804ad42e88b9

commit r13-2900-g001c60ccfeaf9a480a56203418af804ad42e88b9
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Tue Sep 27 10:30:00 2022 +0200

    range-ops: Calculate the popcount of a singleton.
    
    The legacy popcount folding didn't actually fold singleton ranges.
    I don't think anyone noticed because there are match.pd patterns that
    fold __builtin_popcount using the global nonzero bits set by CCP.
    
    It's good form to handle this, even without CCP's help.
    
    Tested on x86-64 Linux.
    
    gcc/ChangeLog:
    
            * gimple-range-op.cc (cfn_popcount): Calculate the popcount of a
            singleton.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/tree-ssa/popcount6b.c: New test.

Diff:
---
 gcc/gimple-range-op.cc                     | 8 ++++++++
 gcc/testsuite/gcc.dg/tree-ssa/popcount6b.c | 6 ++++++
 2 files changed, 14 insertions(+)

diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
index d7c6dfa933d..3f5e5852e5a 100644
--- a/gcc/gimple-range-op.cc
+++ b/gcc/gimple-range-op.cc
@@ -397,6 +397,14 @@ public:
   {
     if (lh.undefined_p ())
       return false;
+    // Calculating the popcount of a singleton is trivial.
+    if (lh.singleton_p ())
+      {
+	wide_int nz = lh.get_nonzero_bits ();
+	wide_int pop = wi::shwi (wi::popcount (nz), TYPE_PRECISION (type));
+	r.set (type, pop, pop);
+	return true;
+      }
     // __builtin_ffs* and __builtin_popcount* return [0, prec].
     int prec = TYPE_PRECISION (lh.type ());
     // If arg is non-zero, then ffs or popcount are non-zero.
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount6b.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount6b.c
new file mode 100644
index 00000000000..90336ecb070
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount6b.c
@@ -0,0 +1,6 @@
+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-evrp -fno-tree-ccp" }
+
+#include "popcount6.c"
+
+// { dg-final { scan-tree-dump "return 1;" "evrp" } }