i386: Fix up -fdollars-in-identifiers with identifiers starting with $ in -masm=att [PR91298]

In AT&T syntax leading $ is special, so if we have identifiers that start
with dollar, we usually fail to assemble it (or assemble incorrectly).
As mentioned in the PR, what works is wrapping the identifiers inside of
parens, like:
	movl	$($a), %eax
	leaq	($a)(,%rdi,4), %rax
	movl	($a)(%rip), %eax
	movl	($a)+16(%rip), %eax
	.globl	$a
	.type	$a, @object
	.size	$a, 72
$a:
	.string	"$a"
	.quad	($a)
(this is x86_64 -fno-pic -O2).  In some places ($a) is not accepted,
like as .globl operand, in .type, .size, so the patch overrides
ASM_OUTPUT_SYMBOL_REF rather than e.g. ASM_OUTPUT_LABELREF.
I didn't want to duplicate what assemble_name is doing (following
transparent aliases), so split assemble_name into two parts; just
mere looking at the first character of a name before calling assemble_name
wouldn't be good enough, a transparent alias could lead from a name
not starting with $ to one starting with it and vice versa.

2020-01-22  Jakub Jelinek  <jakub@redhat.com>

	PR target/91298
	* output.h (assemble_name_resolve): Declare.
	* varasm.c (assemble_name_resolve): New function.
	(assemble_name): Use it.
	* config/i386/i386.h (ASM_OUTPUT_SYMBOL_REF): Define.

	* gcc.target/i386/pr91298-1.c: New test.
	* gcc.target/i386/pr91298-2.c: New test.

1 files changed, 20 insertions, 13 deletions

diff --git a/gcc/varasm.c b/gcc/varasm.c
index 498c5ff..dc6da6c 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -2589,20 +2589,16 @@ assemble_name_raw (FILE *file, const char *name)
     ASM_OUTPUT_LABELREF (file, name);
 }
 
-/* Like assemble_name_raw, but should be used when NAME might refer to
-   an entity that is also represented as a tree (like a function or
-   variable).  If NAME does refer to such an entity, that entity will
-   be marked as referenced.  */
-
-void
-assemble_name (FILE *file, const char *name)
+/* Return NAME that should actually be emitted, looking through
+   transparent aliases.  If NAME refers to an entity that is also
+   represented as a tree (like a function or variable), mark the entity
+   as referenced.  */
+const char *
+assemble_name_resolve (const char *name)
 {
-  const char *real_name;
-  tree id;
+  const char *real_name = targetm.strip_name_encoding (name);
+  tree id = maybe_get_identifier (real_name);
 
-  real_name = targetm.strip_name_encoding (name);
-
-  id = maybe_get_identifier (real_name);
   if (id)
     {
       tree id_orig = id;
@@ -2614,7 +2610,18 @@ assemble_name (FILE *file, const char *name)
       gcc_assert (! TREE_CHAIN (id));
     }
 
-  assemble_name_raw (file, name);
+  return name;
+}
+
+/* Like assemble_name_raw, but should be used when NAME might refer to
+   an entity that is also represented as a tree (like a function or
+   variable).  If NAME does refer to such an entity, that entity will
+   be marked as referenced.  */
+
+void
+assemble_name (FILE *file, const char *name)
+{
+  assemble_name_raw (file, assemble_name_resolve (name));
 }
 
 /* Allocate SIZE bytes writable static space with a gensym name