[gcc r15-34] Verify that reading back from vrange_storage doesn't drop bits.

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

https://gcc.gnu.org/g:92f74ee21218cab08d7bb7769004a65e8a291fa3

commit r15-34-g92f74ee21218cab08d7bb7769004a65e8a291fa3
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Tue Mar 19 16:35:41 2024 +0100

    Verify that reading back from vrange_storage doesn't drop bits.
    
    We have a sanity check in the irange storage code to make sure that
    reading back a cache entry we have just written to yields exactly the
    same range.  There's no need to do this only for integers.  This patch
    moves the code to a more generic place.
    
    However, doing so tickles a latent bug in the frange code where a
    range is being pessimized from [0.0, 1.0] to [-0.0, 1.0].  Exclude
    checking frange's until this bug is fixed.
    
    gcc/ChangeLog:
    
            * value-range-storage.cc (irange_storage::set_irange): Move
            verification code from here...
            (vrange_storage::set_vrange): ...to here.

Diff:
---
 gcc/value-range-storage.cc | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/gcc/value-range-storage.cc b/gcc/value-range-storage.cc
index f00474ad0e6..09a29776a0e 100644
--- a/gcc/value-range-storage.cc
+++ b/gcc/value-range-storage.cc
@@ -165,6 +165,19 @@ vrange_storage::set_vrange (const vrange &r)
     }
   else
     gcc_unreachable ();
+
+  // Verify that reading back from the cache didn't drop bits.
+  if (flag_checking
+      // FIXME: Avoid checking frange, as it currently pessimizes some ranges:
+      //
+      // gfortran.dg/pr49472.f90 pessimizes [0.0, 1.0] into [-0.0, 1.0].
+      && !is_a <frange> (r)
+      && !r.undefined_p ())
+    {
+      Value_Range tmp (r);
+      get_vrange (tmp, r.type ());
+      gcc_checking_assert (tmp == r);
+    }
 }
 
 // Restore R from storage.
@@ -306,13 +319,6 @@ irange_storage::set_irange (const irange &r)
   irange_bitmask bm = r.m_bitmask;
   write_wide_int (val, len, bm.value ());
   write_wide_int (val, len, bm.mask ());
-
-  if (flag_checking)
-    {
-      int_range_max tmp;
-      get_irange (tmp, r.type ());
-      gcc_checking_assert (tmp == r);
-    }
 }
 
 static inline void