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

[Aldy Hernandez via Gcc-patches]

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.
---
 gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c | 15 +++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c | 16 ++++++++++++++++
 gcc/value-range.cc                         |  5 +++++
 3 files changed, 36 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
new file mode 100644
index 00000000000..a0c20dbd4b1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
@@ -0,0 +1,15 @@
+// { dg-do run }
+// { dg-options "-O1 -fno-tree-ccp" }
+
+int a, b;
+int main() {
+  int c = 0;
+  if (a)
+    c = 1;
+  c = 1 & (a && c) && b;
+  if (a) {
+    b = c;
+    __builtin_abort ();
+  }
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c
new file mode 100644
index 00000000000..d447c78bdd3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c
@@ -0,0 +1,16 @@
+// { dg-do run }
+// { dg-options "-O1" }
+
+int a, b;
+int main() {
+  int c = 0;
+  long d;
+  for (; b < 1; b++) {
+    (c && d) & 3 || a;
+    d = c;
+    c = -1;
+    if (d)
+      __builtin_abort();
+  }
+  return 0;
+}
diff --git a/gcc/value-range.cc b/gcc/value-range.cc
index a14f9bc4394..e07d2aa9a5b 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;
 }
 
-- 
2.37.3