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[4.6 PATCH] Workaround for stack slot sharing problems with unrolling (PR fortran/49103)


Hi!

While for the trunk I hope Michael will finalize a much better fix,
this patch provides a quick workaround for 4.6 branch.

In particular, I'd like to avoid reverting the
http://gcc.gnu.org/ml/gcc-patches/2011-01/msg01442.html
patch, because if GIMPLE passes don't do any significant code motion,
sharing the stack slots e.g. for Fortran I/O parameter block helps quite a
bit.  So, what this patch attempts to do is (only for the cases which
changed by the above mentioned patch) make the stack slot sharing
conditional on no significant code motion (loop {,complete} unrolling and other
kind of bb duplication).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for 4.6 branch?
Or is it way too ugly and should I rather revert there my patch?

2011-06-07  Jakub Jelinek  <jakub@redhat.com>

	PR fortran/49103
	* tree.h (DECL_NONSHAREABLE): Define.
	(struct tree_decl_common): Change decl_common_unused to
	decl_nonshareable_flag.
	* cfgexpand.c (expand_used_vars_for_block, clear_tree_used):
	Ignore vars with DECL_NONSHAREABLE bit set.
	* tree-cfg.c (gimple_duplicate_bb): Set DECL_NONSHAREABLE
	on stores to automatic aggregate vars.

	* gfortran.dg/pr49103.f90: New test.

--- gcc/tree.h.jj	2011-03-14 14:12:15.000000000 +0100
+++ gcc/tree.h	2011-05-31 14:05:34.000000000 +0200
@@ -1330,6 +1330,10 @@ extern void omp_clause_range_check_faile
 #define DECL_READ_P(NODE) \
   (TREE_CHECK2 (NODE, VAR_DECL, PARM_DECL)->decl_common.decl_read_flag)
 
+#define DECL_NONSHAREABLE(NODE) \
+  (TREE_CHECK2 (NODE, VAR_DECL, \
+		RESULT_DECL)->decl_common.decl_nonshareable_flag)
+
 /* In a CALL_EXPR, means that the call is the jump from a thunk to the
    thunked-to function.  */
 #define CALL_FROM_THUNK_P(NODE) (CALL_EXPR_CHECK (NODE)->base.protected_flag)
@@ -2787,8 +2791,9 @@ struct GTY(()) tree_decl_common {
      being set.  */
   unsigned decl_read_flag : 1;
 
-  /* Padding so that 'off_align' can be on a 32-bit boundary.  */
-  unsigned decl_common_unused : 1;
+  /* In VAR_DECL or RESULT_DECL set when significant code movement precludes
+     attempting to share the stack slot with some other variable.  */
+  unsigned decl_nonshareable_flag : 1;
 
   /* DECL_OFFSET_ALIGN, used only for FIELD_DECLs.  */
   unsigned int off_align : 8;
--- gcc/cfgexpand.c.jj	2011-05-04 10:46:52.000000000 +0200
+++ gcc/cfgexpand.c	2011-05-31 14:08:36.000000000 +0200
@@ -1134,7 +1134,9 @@ expand_used_vars_for_block (tree block, 
 
   /* Expand all variables at this level.  */
   for (t = BLOCK_VARS (block); t ; t = DECL_CHAIN (t))
-    if (TREE_USED (t))
+    if (TREE_USED (t)
+        && ((TREE_CODE (t) != VAR_DECL && TREE_CODE (t) != RESULT_DECL)
+	    || !DECL_NONSHAREABLE (t)))
       expand_one_var (t, toplevel, true);
 
   this_sv_num = stack_vars_num;
@@ -1167,6 +1169,8 @@ clear_tree_used (tree block)
 
   for (t = BLOCK_VARS (block); t ; t = DECL_CHAIN (t))
     /* if (!TREE_STATIC (t) && !DECL_EXTERNAL (t)) */
+    if ((TREE_CODE (t) != VAR_DECL && TREE_CODE (t) != RESULT_DECL)
+	|| !DECL_NONSHAREABLE (t))
       TREE_USED (t) = 0;
 
   for (t = BLOCK_SUBBLOCKS (block); t ; t = BLOCK_CHAIN (t))
--- gcc/tree-cfg.c.jj	2011-03-14 14:12:15.000000000 +0100
+++ gcc/tree-cfg.c	2011-05-31 15:22:14.000000000 +0200
@@ -5117,6 +5117,7 @@ gimple_duplicate_bb (basic_block bb)
     {
       def_operand_p def_p;
       ssa_op_iter op_iter;
+      tree lhs;
 
       stmt = gsi_stmt (gsi);
       if (gimple_code (stmt) == GIMPLE_LABEL)
@@ -5130,6 +5131,29 @@ gimple_duplicate_bb (basic_block bb)
       maybe_duplicate_eh_stmt (copy, stmt);
       gimple_duplicate_stmt_histograms (cfun, copy, cfun, stmt);
 
+      /* When copying around a stmt writing into a local non-user
+	 aggregate, make sure it won't share stack slot with other
+	 vars.  */
+      lhs = gimple_get_lhs (stmt);
+      if (lhs
+	  && (handled_component_p (lhs)
+	      || TREE_CODE (lhs) == MEM_REF
+	      || TREE_CODE (lhs) == TARGET_MEM_REF
+	      || TREE_CODE (lhs) == VAR_DECL
+	      || TREE_CODE (lhs) == RESULT_DECL))
+	{
+	  tree base = get_base_address (lhs);
+	  if (base
+	      && (TREE_CODE (base) == VAR_DECL
+		  || TREE_CODE (base) == RESULT_DECL)
+	      && DECL_IGNORED_P (base)
+	      && !TREE_STATIC (base)
+	      && !DECL_EXTERNAL (base)
+	      && (TREE_CODE (base) != VAR_DECL
+		  || !DECL_HAS_VALUE_EXPR_P (base)))
+	    DECL_NONSHAREABLE (base) = 1;
+	}
+
       /* Create new names for all the definitions created by COPY and
 	 add replacement mappings for each new name.  */
       FOR_EACH_SSA_DEF_OPERAND (def_p, copy, op_iter, SSA_OP_ALL_DEFS)
--- gcc/testsuite/gfortran.dg/pr49103.f90.jj	2011-05-31 13:52:43.000000000 +0200
+++ gcc/testsuite/gfortran.dg/pr49103.f90	2011-05-31 13:57:16.000000000 +0200
@@ -0,0 +1,19 @@
+! PR fortran/49103
+! { dg-do run }
+  integer :: a(2), b(2), i, j
+  open (10, status='scratch')
+  do j = 1, 2
+    a = (/ 0, 0 /)
+    b = (/ 1, 1 /)
+    do i = 1, 2
+      write (10, *) a
+      write (10, *) b
+    end do
+  end do
+  rewind (10)
+  do i = 0, 7
+    read (10, *) a
+    if (any (a .ne. mod (i, 2))) call abort
+  end do
+  close (10)
+end

	Jakub


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