ipa-devirt: check precision mismatch of enum values [PR101396]

We are comparing enum values (in wide_int) to check ODR violation.
However, if we compare two wide_int values with different precision,
we'll trigger an assert, leading to ICE.  With enum-base introduced
in C++11, it's easy to sink into this situation.

To fix the issue, we need to explicitly check this kind of mismatch,
and emit a proper warning message if there is such one.

gcc/

	PR ipa/101396
	* ipa-devirt.c (ipa_odr_read_section): Compare the precision of
	  enum values, and emit a warning if they mismatch.

gcc/testsuite/

	PR ipa/101396
	* g++.dg/lto/pr101396_0.C: New test.
	* g++.dg/lto/pr101396_1.C: New test.

gcc/ipa-devirt.c

@@ -4193,6 +4193,8 @@ ipa_odr_read_section (struct lto_file_decl_data *file_data, const char *data,
 	      if (do_warning != -1 || j >= this_enum.vals.length ())
 		continue;
 	      if (strcmp (id, this_enum.vals[j].name)
+		  || (val.get_precision() !=
+		      this_enum.vals[j].val.get_precision())
 		  || val != this_enum.vals[j].val)
 		{
 		  warn_name = xstrdup (id);
@@ -4260,6 +4262,13 @@ ipa_odr_read_section (struct lto_file_decl_data *file_data, const char *data,
 			    "name %qs differs from name %qs defined"
 			    " in another translation unit",
 			    this_enum.vals[j].name, warn_name);
+		  else if (this_enum.vals[j].val.get_precision() !=
+			   warn_value.get_precision())
+		    inform (this_enum.vals[j].locus,
+			    "name %qs is defined as %u-bit while another "
+			    "translation unit defines it as %u-bit",
+			    warn_name, this_enum.vals[j].val.get_precision(),
+			    warn_value.get_precision());
 		  /* FIXME: In case there is easy way to print wide_ints,
 		     perhaps we could do it here instead of overflow check.  */
 		  else if (wi::fits_shwi_p (this_enum.vals[j].val)

gcc/testsuite/g++.dg/lto/pr101396_0.C

@@ -0,0 +1,12 @@
+/* { dg-lto-do link } */
+
+enum A : __UINT32_TYPE__ { // { dg-lto-warning "6: type 'A' violates the C\\+\\+ One Definition Rule" }
+  a, // { dg-lto-note "3: name 'a' is defined as 32-bit while another translation unit defines it as 64-bit" }
+  b,
+  c
+};
+
+int main()
+{
+  return (int) A::a;
+}

gcc/testsuite/g++.dg/lto/pr101396_1.C

@@ -0,0 +1,10 @@
+enum A : __UINT64_TYPE__ { // { dg-lto-note "6: an enum with different value name is defined in another translation unit" }
+  a, // { dg-lto-note "3: mismatching definition" }
+  b,
+  c
+};
+
+int f(enum A x)
+{
+  return (int) x;
+}