Handle setting of 1-bit anti-ranges uniformly.

PR tree-optimization/99296
	* value-range.cc (irange::irange_set_1bit_anti_range): New.
	(irange::irange_set_anti_range): Call irange_set_1bit_anti_range
	* value-range.h (irange::irange_set_1bit_anti_range): New.

gcc/testsuite/gcc.dg/pr99296.c

@@ -0,0 +1,7 @@
+// { dg-do compile }
+// { dg-options "-O2 -fno-tree-bit-ccp" }
+
+struct {
+  signed a : 1;
+} b, c;
+void d() { b.a |= c.a |= 0 != 2; }

gcc/value-range.cc

@@ -184,12 +184,43 @@ irange::irange_set (tree min, tree max)
     verify_range ();
 }
 
+void
+irange::irange_set_1bit_anti_range (tree min, tree max)
+{
+  tree type = TREE_TYPE (min);
+  gcc_checking_assert (TYPE_PRECISION (type) == 1);
+
+  if (operand_equal_p (min, max))
+    {
+      // Since these are 1-bit quantities, they can only be [MIN,MIN]
+      // or [MAX,MAX].
+      if (vrp_val_is_min (min))
+	min = max = vrp_val_max (type);
+      else
+	min = max = vrp_val_min (type);
+      set (min, max);
+    }
+  else
+    {
+      // The only alternative is [MIN,MAX], which is the empty range.
+      set_undefined ();
+    }
+  if (flag_checking)
+    verify_range ();
+}
+
 void
 irange::irange_set_anti_range (tree min, tree max)
 {
   gcc_checking_assert (!POLY_INT_CST_P (min));
   gcc_checking_assert (!POLY_INT_CST_P (max));
 
+  if (TYPE_PRECISION (TREE_TYPE (min)) == 1)
+    {
+      irange_set_1bit_anti_range (min, max);
+      return;
+    }
+
   // set an anti-range
   tree type = TREE_TYPE (min);
   signop sign = TYPE_SIGN (type);

gcc/value-range.h

@@ -127,6 +127,8 @@ protected:
   void copy_legacy_to_multi_range (const irange &);
 
 private:
+  void irange_set_1bit_anti_range (tree, tree);
+
   unsigned char m_num_ranges;
   unsigned char m_max_ranges;
   ENUM_BITFIELD(value_range_kind) m_kind : 8;