[PR107195] Set range to zero when nonzero mask is 0.

When solving 0 = _15 & 1, we calculate _15 as:

	[irange] int [-INF, -2][0, +INF] NONZERO 0xfffffffe

The known value of _15 is [0, 1] NONZERO 0x1 which is intersected with
the above, yielding:

	[0, 1] NONZERO 0x0

This eventually gets copied to a _Bool [0, 1] NONZERO 0x0.

This is problematic because here we have a bool which is zero, but
returns false for irange::zero_p, since the latter does not look at
nonzero bits.  This causes logical_combine to assume the range is
not-zero, and all hell breaks loose.

I think we should just normalize a nonzero mask of 0 to [0, 0] at
creation, thus avoiding all this.

	PR tree-optimization/107195

gcc/ChangeLog:

	* value-range.cc (irange::set_range_from_nonzero_bits): Set range
	to [0,0] when nonzero mask is 0.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr107195-1.c: New test.
	* gcc.dg/tree-ssa/pr107195-2.c: New test.

1 files changed, 5 insertions, 0 deletions

diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index a14f9bc..e07d2aa 100644
--- a/gcc/value-range.cc
+++ b/gcc/value-range.cc
@@ -2903,6 +2903,11 @@ irange::set_range_from_nonzero_bits ()
 	}
       return true;
     }
+  else if (popcount == 0)
+    {
+      set_zero (type ());
+      return true;
+    }
   return false;
 }