[PATCH] Don't emit unreferenced static storage compound literals

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

The following patch seem to work to avoid emitting unreferenced compound
literals (be it because of the initialization by compound literal GCC
extension or because of sizeof() or other reason).
Although it is an optimization, I wonder if this could be commited for 3.1,
because e.g.
size_t x = sizeof((int i[4096]) { 1 });
or
struct fourkb x = (struct fourkb) { 1, 2, 3 };
will really make notticeable size difference.
In Linux kernel AFAIK this is used mostly for small objects, on the other
side there is lots of them.

2002-01-03  Jakub Jelinek  <jakub@redhat.com>

	* c-decl.c (build_compound_literal): Defer compound literal decls
	until until file end to emit them only if they are actually used.

	* gcc.dg/gnu89-init-2.c: New test.

--- gcc/testsuite/gcc.dg/gnu89-init-2.c.jj	Thu Jan  3 01:51:55 2002
+++ gcc/testsuite/gcc.dg/gnu89-init-2.c	Thu Jan  3 02:04:58 2002
@@ -0,0 +1,25 @@
+/* Test whether __compound_literal.* objects are not emitted unless
+   they are actually needed.  */
+/* Origin: Jakub Jelinek <jakub@redhat.com> */
+/* { dg-do compile } */
+/* { dg-options "-std=gnu89 -O2" } */
+/* { dg-final { scan-assembler-not "__compound_literal" } } */
+
+struct A { int i; int j; int k[4]; };
+struct B { };
+struct C { int i; };
+struct D { int i; struct C j; };
+
+struct A a = (struct A) { .j = 6, .k[2] = 12 };
+struct B b = (struct B) { };
+int c[] = (int []) { [2] = 6, 7, 8 };
+int d[] = (int [3]) { 1 };
+int e[2] = (int []) { 1, 2 };
+int f[2] = (int [2]) { 1 };
+struct C g[3] = { [2] = (struct C) { 13 }, [1] = (const struct C) { 12 } };
+struct D h = { .j = (struct C) { 15 }, .i = 14 };
+struct D i[2] = { [1].j = (const struct C) { 17 },
+		  [0] = { 0, (struct C) { 16 } } };
+static const int *j = 1 ? (const int *) 0 : & (const int) { 26 };
+int k = (int) sizeof ((int [6]) { 1, 2, 3, 4, 5, 6 }) + 4;
+int l = (int) sizeof ((struct C) { 16 });
--- gcc/c-decl.c.jj	Thu Jan  3 02:01:40 2002
+++ gcc/c-decl.c	Thu Jan  3 02:07:20 2002
@@ -3877,12 +3877,18 @@ build_compound_literal (type, init)
   if (TREE_STATIC (decl))
     {
       /* This decl needs a name for the assembler output.  We also need
-	 a unique suffix to be added to the name, for which DECL_CONTEXT
-	 must be set.  */
-      DECL_NAME (decl) = get_identifier ("__compound_literal");
-      DECL_CONTEXT (decl) = complit;
+	 a unique suffix to be added to the name.  */
+      char *name;
+      extern int var_labelno;
+
+      ASM_FORMAT_PRIVATE_NAME (name, "__compound_literal", var_labelno);
+      var_labelno++;
+      DECL_NAME (decl) = get_identifier (name);
+      DECL_DEFER_OUTPUT (decl) = 1;
+      DECL_COMDAT (decl) = 1;
+      DECL_ARTIFICIAL (decl) = 1;
+      pushdecl (decl);
       rest_of_decl_compilation (decl, NULL, 1, 0);
-      DECL_CONTEXT (decl) = NULL_TREE;
     }
 
   return complit;

	Jakub