[gcc r9-9418] varasm: Fix ICE with -fsyntax-only [PR99035]

[gcc r9-9418] varasm: Fix ICE with -fsyntax-only [PR99035]

[Jakub Jelinek]

https://gcc.gnu.org/g:6496e9154309cbd911f944147da1246628e393da

commit r9-9418-g6496e9154309cbd911f944147da1246628e393da
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Feb 10 19:52:37 2021 +0100

    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.
    
    (cherry picked from commit a964f494cd5a90f631b8c0c01777a9899e0351ce)

Diff:
---
 gcc/testsuite/g++.dg/ext/weak6.C | 8 ++++++++
 gcc/varasm.c                     | 7 ++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/g++.dg/ext/weak6.C b/gcc/testsuite/g++.dg/ext/weak6.C
new file mode 100644
index 00000000000..e9a70ee0dad
--- /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 8d87e28cc7c..7749be05b6f 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -5670,7 +5670,12 @@ 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);