varasm: Fix ICE with -fsyntax-only [PR99035]

My FE change from 2 years ago uses TREE_ASM_WRITTEN in -fsyntax-only
mode more aggressively to avoid "expanding" functions multiple times.
With -fsyntax-only nothing is really expanded, so I think it is acceptable
to adjust the assert and allow declare_weak at any time, with -fsyntax-only
we know it is during parsing only anyway.

2021-02-10  Jakub Jelinek  <jakub@redhat.com>

	PR c++/99035
	* varasm.c (declare_weak): For -fsyntax-only, allow even
	TREE_ASM_WRITTEN function decls.

	* g++.dg/ext/weak6.C: New test.

diff --git a/gcc/testsuite/g++.dg/ext/weak6.C b/gcc/testsuite/g++.dg/ext/weak6.C
new file mode 100644 (file)
index 0000000..e9a70ee
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/weak6.C
@@ -0,0 +1,8 @@
+// PR c++/99035
+// { dg-do compile }
+// { dg-require-weak "" }
+// { dg-options "-fsyntax-only" }
+
+extern void * foo (void);
+void * foo (void) { return (void *)foo; }
+#pragma weak foo

diff --git a/gcc/varasm.c b/gcc/varasm.c
index 21be03aeba2cb1ee78eb6bc4077133ba356615de..29478ab0d8d563a420c49e056220a8e0a3873731 100644 (file)
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -5927,7 +5927,12 @@ merge_weak (tree newdecl, tree olddecl)
 void
 declare_weak (tree decl)
 {
-  gcc_assert (TREE_CODE (decl) != FUNCTION_DECL || !TREE_ASM_WRITTEN (decl));
+  /* With -fsyntax-only, TREE_ASM_WRITTEN might be set on certain function
+     decls earlier than normally, but as with -fsyntax-only nothing is really
+     emitted, there is no harm in marking it weak later.  */
+  gcc_assert (TREE_CODE (decl) != FUNCTION_DECL
+             || !TREE_ASM_WRITTEN (decl)
+             || flag_syntax_only);
   if (! TREE_PUBLIC (decl))
     {
       error ("weak declaration of %q+D must be public", decl);