Hi!
The C FE just warns and doesn't override builtins, but C++ FE
on say int __builtin_trap (); will override the builtin, so later
builtin_decl_explicit will return the bogus user function which e.g.
doesn't have any merged attributes, can have different arguments or
return type etc.
This patch prevents that; generally the builtins we want to override
are the DECL_ANTICIPATED which we handle properly earlier.
The testcase in the PR ICEs not because of the argument mismatch (there is
none in this case) or return value mismatch (because nothing cares about the
return value), but because the new decl lacks noreturn attribute and GCC
relies on builtin_decl_explicit (BUILT_IN_TRAP) to be really noreturn.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or shall we error on these, or ignore the name checks and just
if (DECL_BUILT_IN (olddecl)) return NULL_TREE;, something else?
2018-03-08 Jakub Jelinek <ja...@redhat.com>
PR c++/84724
* decl.c (duplicate_decls): Don't override __* prefixed builtins
except for __[^b]*_chk.
* g++.dg/ext/pr84724.C: New test.
--- gcc/cp/decl.c.jj 2018-03-05 17:23:45.901130856 +0100
+++ gcc/cp/decl.c 2018-03-08 10:28:55.574179119 +0100
@@ -1578,6 +1578,28 @@ next_arg:;
DECL_BUILT_IN (olddecl)
? G_("shadowing built-in function %q#D")
: G_("shadowing library function %q#D"), olddecl);
+ /* Don't really override olddecl for __* prefixed builtins
+ except for __[^b]*_chk, the compiler might be using those
+ explicitly. */
+ if (DECL_BUILT_IN (olddecl))
+ {
+ tree id = DECL_NAME (olddecl);
+ const char *name = IDENTIFIER_POINTER (id);
+
+ if (name[0] == '_' && name[1] == '_')
+ {
+ if (strncmp (name + 2, "builtin_",
+ strlen ("builtin_")) == 0)
+ return NULL_TREE;
+
+ size_t len = strlen (name);
+
+ if (len <= strlen ("___chk")
+ || memcmp (name + len - strlen ("_chk"),
+ "_chk", strlen ("_chk") + 1) != 0)
+ return NULL_TREE;
+ }
+ }
}
else
/* Discard the old built-in function. */
--- gcc/testsuite/g++.dg/ext/pr84724.C.jj 2018-03-08 10:31:03.683183914
+0100
+++ gcc/testsuite/g++.dg/ext/pr84724.C 2018-03-08 10:30:45.489183233 +0100
@@ -0,0 +1,13 @@
+// PR c++/84724
+// { dg-do compile }
+// { dg-options "-O3 -fpermissive" }
+
+int __builtin_trap (); // { dg-warning "ambiguates built-in
declaration" }
+
+int
+foo ()
+{
+ int b;
+ int c (&b); // { dg-warning "invalid conversion from" }
+ return b %= b ? c : 0;
+}
Jakub
