no bareword_filehandes: don't look up class barewords as handles

This prevents SomeBareword from being looked up as a filehandle:

  no feature "bareword_filehandles";
  SomeBareword->method();

Since "bareword_filehandles" is explicitly about bareword handles,
it does not prevent other string to object/class look ups from
resolving the class as a filehandle, eg for the following:

  "SomeLiteral"->method();
  my $x = "SomeVariable";
  $x->method();

both are looked up as file handles per normal.

Note that in any of these cases, with or without the
bareword_filehandles feature, if the name is a bareword that
has been resolved as a class name since the last time the
stash cache was cleared, it will be resolved as a class name,
not a filehandle.

Fixes Perl#19426

# Conflicts:
#	opcode.h

# Conflicts:
#	opcode.h

embed.fnc

@@ -4714,6 +4714,8 @@ S	|void	|inplace_aassign|NN OP *o
 RST	|bool	|is_handle_constructor					\
 				|NN const OP *o 			\
 				|I32 numargs
+Ti	|bool	|is_standard_filehandle_name				\
+				|NN const char *fhname
 S	|OP *	|listkids	|NULLOK OP *o
 S	|bool	|looks_like_bool|NN const OP *o
 S	|OP *	|modkids	|NULLOK OP *o				\

embed.h

@@ -1435,6 +1435,7 @@
 #     define gen_constant_list(a)               S_gen_constant_list(aTHX_ a)
 #     define inplace_aassign(a)                 S_inplace_aassign(aTHX_ a)
 #     define is_handle_constructor              S_is_handle_constructor
+#     define is_standard_filehandle_name        S_is_standard_filehandle_name
 #     define listkids(a)                        S_listkids(aTHX_ a)
 #     define looks_like_bool(a)                 S_looks_like_bool(aTHX_ a)
 #     define modkids(a,b)                       S_modkids(aTHX_ a,b)

op.c

@@ -712,17 +712,27 @@ Perl_no_bareword_allowed(pTHX_ OP *o)
     o->op_private &= ~OPpCONST_STRICT; /* prevent warning twice about the same OP */
 }
 
+/*
+Return true if the supplied string is the name of one of the built-in
+filehandles.
+*/
+
+PERL_STATIC_INLINE bool
+S_is_standard_filehandle_name(const char *fhname) {
+    return strEQ(fhname, "STDERR")
+        || strEQ(fhname, "STDOUT")
+        || strEQ(fhname, "STDIN")
+        || strEQ(fhname, "_")
+        || strEQ(fhname, "ARGV")
+        || strEQ(fhname, "ARGVOUT")
+        || strEQ(fhname, "DATA");
+}
+
 void
 Perl_no_bareword_filehandle(pTHX_ const char *fhname) {
     PERL_ARGS_ASSERT_NO_BAREWORD_FILEHANDLE;
 
-    if (strNE(fhname, "STDERR")
-        && strNE(fhname, "STDOUT")
-        && strNE(fhname, "STDIN")
-        && strNE(fhname, "_")
-        && strNE(fhname, "ARGV")
-        && strNE(fhname, "ARGVOUT")
-        && strNE(fhname, "DATA")) {
+    if (!is_standard_filehandle_name(fhname)) {
         qerror(Perl_mess(aTHX_ "Bareword filehandle \"%s\" not allowed under 'no feature \"bareword_filehandles\"'", fhname));
     }
 }
@@ -14845,6 +14855,7 @@ Perl_ck_subr(pTHX_ OP *o)
     CV *cv;
     GV *namegv;
     SV **const_class = NULL;
+    OP *const_op = NULL;
 
     PERL_ARGS_ASSERT_CK_SUBR;
 
@@ -14874,20 +14885,29 @@ Perl_ck_subr(pTHX_ OP *o)
             if (aop->op_type == OP_CONST) {
                 aop->op_private &= ~OPpCONST_STRICT;
                 const_class = &cSVOPx(aop)->op_sv;
+                const_op = aop;
             }
             else if (aop->op_type == OP_LIST) {
                 OP * const sib = OpSIBLING(cUNOPx(aop)->op_first);
                 if (sib && sib->op_type == OP_CONST) {
                     sib->op_private &= ~OPpCONST_STRICT;
                     const_class = &cSVOPx(sib)->op_sv;
+                    const_op = sib;
                 }
             }
             /* make class name a shared cow string to speedup method calls */
             /* constant string might be replaced with object, f.e. bigint */
             if (const_class && SvPOK(*const_class)) {
+                assert(const_op);
                 STRLEN len;
                 const char* str = SvPV(*const_class, len);
                 if (len) {
+                    if (!FEATURE_BAREWORD_FILEHANDLES_IS_ENABLED
+                        && !is_standard_filehandle_name(str)
+                        && (const_op->op_private & OPpCONST_BARE)) {
+                        cvop->op_private |= OPpMETH_NO_BAREWORD_IO;
+                    }
+
                     SV* const shared = newSVpvn_share(
                         str, SvUTF8(*const_class)
                                     ? -(SSize_t)len : (SSize_t)len,