[PATCH] Optimize initialization from compound literals (PR tree-optimization/33723)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

If the address of an compound literal is never taken and it is only
used as initializer to some variable, I believe a conforming program
can't find out whether we are first initializing some anonymous variable
and then copying that anonymous variable to the user var, or initializing
that user var directly.  When SRA is not able to scalarize it (as shown
by the testcase which is modelled from using e.g.
mutex = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
condvar = (pthread_cond_t) PTHREAD_COND_INITIALIZER;
or
rwlock = (pthread_rwlock_t) PTHREAD_RWLOCK_INITIALIZER;
with glibc), this then survives until assembly.
The following patch optimizes this by initializing the variable to
the initializer of the compound literal if it's address has never been
taken.  The generated assembly looks much better on x86_64-linux.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2007-10-29  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/33723
	* c-gimplify.c (c_gimplify_expr): Optimize INIT_EXPR or
	MODIFY_EXPR with non-addressable COMPOUND_LITERAL_EXPR as source.

	* gcc.c-torture/execute/20071029-1.c: New test.
	* gcc.dg/tree-ssa/pr33723.c: New test.

--- gcc/c-gimplify.c.jj	2007-08-13 15:11:18.000000000 +0200
+++ gcc/c-gimplify.c	2007-10-29 20:21:02.000000000 +0100
@@ -233,6 +233,29 @@ c_gimplify_expr (tree *expr_p, tree *pre
     case COMPOUND_LITERAL_EXPR:
       return gimplify_compound_literal_expr (expr_p, pre_p);
 
+    case INIT_EXPR:
+    case MODIFY_EXPR:
+      if (TREE_CODE (TREE_OPERAND (*expr_p, 1)) == COMPOUND_LITERAL_EXPR)
+	{
+	  tree complit = TREE_OPERAND (*expr_p, 1);
+	  tree decl_s = COMPOUND_LITERAL_EXPR_DECL_STMT (complit);
+	  tree decl = DECL_EXPR_DECL (decl_s);
+	  tree init = DECL_INITIAL (decl);
+
+	  /* struct T x = (struct T) { 0, 1, 2 } can be optimized
+	     into struct T x = { 0, 1, 2 } if the address of the
+	     compound literal has never been taken.  */
+	  if (!TREE_ADDRESSABLE (complit)
+	      && !TREE_ADDRESSABLE (decl)
+	      && init)
+	    {
+	      *expr_p = copy_node (*expr_p);
+	      TREE_OPERAND (*expr_p, 1) = init;
+	      return GS_OK;
+	    }
+	}
+      return GS_UNHANDLED;
+
     default:
       return GS_UNHANDLED;
     }
--- gcc/testsuite/gcc.c-torture/execute/20071029-1.c.jj	2007-10-29 20:12:52.000000000 +0100
+++ gcc/testsuite/gcc.c-torture/execute/20071029-1.c	2007-10-29 20:12:26.000000000 +0100
@@ -0,0 +1,56 @@
+extern void exit (int);
+extern void abort (void);
+
+typedef union
+{
+  struct
+  {
+    int f1, f2, f3, f4, f5, f6, f7, f8;
+    long int f9, f10;
+    int f11;
+  } f;
+  char s[56];
+  long int a;
+} T;
+
+__attribute__((noinline))
+void
+test (T *t)
+{
+  static int i = 11;
+  if (t->f.f1 != i++)
+    abort ();
+  if (t->f.f2 || t->f.f3 || t->f.f4 || t->f.f5 || t->f.f6
+      || t->f.f7 || t->f.f8 || t->f.f9 || t->f.f10 || t->f.f11)
+    abort ();
+  if (i == 20)
+    exit (0);
+}
+
+__attribute__((noinline))
+void
+foo (int i)
+{
+  T t;
+again:
+  t = (T) { { ++i, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } };
+  test (&t);
+  goto again;
+}
+
+int
+main (void)
+{
+  T *t1, *t2;
+  int cnt = 0;
+  t1 = (T *) 0;
+loop:
+  t2 = t1;
+  t1 = & (T) { .f.f9 = cnt++ };
+  if (cnt < 3)
+    goto loop;
+  if (t1 != t2 || t1->f.f9 != 2)
+    abort ();
+  foo (10);
+  return 0;
+}
--- gcc/testsuite/gcc.dg/tree-ssa/pr33723.c.jj	2007-10-29 20:13:24.000000000 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/pr33723.c	2007-10-29 20:16:18.000000000 +0100
@@ -0,0 +1,74 @@
+/* PR tree-optimization/33723 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-gimple" } */
+
+typedef union
+{
+  struct
+  {
+    int f1, f2, f3, f4, f5, f6, f7, f8;
+    long int f9, f10;
+    int f11;
+  } f;
+  char s[56];
+  long int a;
+} T;
+
+void
+foo1 (void)
+{
+  T t;
+  t = (T) { { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } };
+  test (&t);
+}
+
+void
+bar1 (void)
+{
+  T t = { { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } };
+  test (&t);
+}
+
+void
+baz1 (void)
+{
+  T t;
+  t = (const T) { { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } };
+  test (&t);
+}
+
+void
+foo2 (void)
+{
+  T t;
+  t = (T) { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 } };
+  test (&t);
+}
+
+void
+bar2 (void)
+{
+  T t = { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 } };
+  test (&t);
+}
+
+void
+baz2 (void)
+{
+  T t;
+  t = (const T) { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 } };
+  test (&t);
+}
+
+void
+baz3 (void)
+{
+  T t;
+  t = (const T) (T) { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 } };
+  test (&t);
+}
+
+/* { dg-final { scan-tree-dump-times "t = {}" 3 "gimple"} } */
+/* { dg-final { scan-tree-dump-times "t.f.f1 = 1" 4 "gimple"} } */
+/* { dg-final { scan-tree-dump-times "t.f.f8 = 8" 4 "gimple"} } */
+/* { dg-final { cleanup-tree-dump "gimple" } } */

	Jakub