GCC Status Report (2004-03-09)

Jakub Jelinek jakub@redhat.com
Mon Mar 29 14:10:00 GMT 2004


On Sat, Mar 20, 2004 at 12:04:02PM +0100, Eric Botcazou wrote:
>  2004-03-20  Eric Botcazou <ebotcazou@libertysurf.fr>
>              Mark Mitchell <mark@codesourcery.com>
> 
>         PR optimization/13424
> 	* explow.c (maybe_set_unchanging): Revert 2003-04-07 patch.
> 	* tree.h (readwrite_fields_p): New prototype.
> 	* alias.c (readwrite_fields_p): New function.
>         * expr.c (store_constructor): When clearing the aggregate because of
> 	an incomplete or mostly zero constructor, do not put the /u flag if the
> 	target is already unchanging.  Record whether a non-unchanging
> 	aggregate containing read-write fields is cleared with the /u flag.
> 	In that case, emit a blockage right after the clearing.

Is this patch going to be used for gcc-3_4-branch or are we looking for a
different solution?

If the former, IMHO we need a small follow-up attached below.
If a decl is DECL_EXTERNAL, it probably has no DECL_INITIAL but still
is always ok to have RTX_UNCHANGING_P - it is not initialized in the current
routine.

2004-03-29  Jakub Jelinek  <jakub@redhat.com>

	PR optimization/12419
	* explow.c (maybe_set_unchanging): Set RTX_UNCHANGING_P even for
	read-only DECL_EXTERNAL decls.

	* gcc.dg/20040302-1.c: New test.

--- gcc/explow.c.jj	2003-12-15 09:37:32.000000000 +0100
+++ gcc/explow.c	2004-03-02 12:07:55.034840235 +0100
@@ -600,7 +600,8 @@ maybe_set_unchanging (rtx ref, tree t)
      first case, and decls with TREE_CONSTANT initializers in the second.  */
 
   if ((TREE_READONLY (t) && DECL_P (t)
-       && (TREE_CODE (t) == PARM_DECL
+       && (DECL_EXTERNAL (t)
+	   || TREE_CODE (t) == PARM_DECL
 	   || (DECL_INITIAL (t) && TREE_CONSTANT (DECL_INITIAL (t)))))
       || TREE_CODE_CLASS (TREE_CODE (t)) == 'c')
     RTX_UNCHANGING_P (ref) = 1;
--- gcc/testsuite/gcc.dg/20040302-1.c.jj	2004-01-21 17:12:41.000000000 +0100
+++ gcc/testsuite/gcc.dg/20040302-1.c	2004-03-03 00:08:25.449237291 +0100
@@ -0,0 +1,18 @@
+/* PR optimization/12419 */
+/* Ensure external_const_array[0] is read just once.  */
+/* { dg-do compile { target i?86-*-linux* x86_64-*-linux* } } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler "external_const_array" } } */
+/* { dg-final { scan-assembler-not "external_const_array.*add\[^\\n\]*external_const_array" } } */
+
+extern const int external_const_array [];
+extern void foo (void);
+
+int
+bar (void)
+{
+  int n = external_const_array[0];
+  foo ();
+  n += external_const_array[0];
+  return n;
+}


	Jakub



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