re PR c++/51060 (Temporary object stack space is not re-used)

	PR c++/51060
	* gimplify.c (gimplify_target_expr): Add a clobber to the cleanup.
	(gimplify_modify_expr): Don't try to simplify it.
	* cp/cp-gimplify.c (cp_gimplify_expr): Leave clobbers alone.

From-SVN: r181332

6 files changed, 87 insertions, 3 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f3e745f..e90d1f6 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2011-11-12  Jason Merrill  <jason@redhat.com>
+
+	PR c++/51060
+	* gimplify.c (gimplify_target_expr): Add a clobber to the cleanup.
+	(gimplify_modify_expr): Don't try to simplify it.
+
 2011-11-12  Dimitrios Apostolou  <jimis@gmx.net>
 
 	PR bootstrap/51094
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 291487f..21f6447 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2011-11-12  Jason Merrill  <jason@redhat.com>
+
+	PR c++/51060
+	* cp-gimplify.c (cp_gimplify_expr): Leave clobbers alone.
+
 2011-11-11  Ed Smith-Rowland  <3dw4rd@verizon.net>
 
 	PR c++/50976
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index af45f59..9968c3d 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -569,7 +569,8 @@ cp_gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 
 	else if ((is_gimple_lvalue (op1) || INDIRECT_REF_P (op1)
 		  || (TREE_CODE (op1) == CONSTRUCTOR
-		      && CONSTRUCTOR_NELTS (op1) == 0)
+		      && CONSTRUCTOR_NELTS (op1) == 0
+		      && !TREE_CLOBBER_P (op1))
 		  || (TREE_CODE (op1) == CALL_EXPR
 		      && !CALL_EXPR_RETURN_SLOT_OPT (op1)))
 		 && is_really_empty_class (TREE_TYPE (op0)))
diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index 9845b69..cfe6696 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -4554,6 +4554,16 @@ gimplify_modify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
   gcc_assert (TREE_CODE (*expr_p) == MODIFY_EXPR
 	      || TREE_CODE (*expr_p) == INIT_EXPR);
 
+  /* Trying to simplify a clobber using normal logic doesn't work,
+     so handle it here.  */
+  if (TREE_CLOBBER_P (*from_p))
+    {
+      gcc_assert (!want_value && TREE_CODE (*to_p) == VAR_DECL);
+      gimplify_seq_add_stmt (pre_p, gimple_build_assign (*to_p, *from_p));
+      *expr_p = NULL;
+      return GS_ALL_DONE;
+    }
+
   /* Insert pointer conversions required by the middle-end that are not
      required by the frontend.  This fixes middle-end type checking for
      for example gcc.dg/redecl-6.c.  */
@@ -5335,6 +5345,8 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 
   if (init)
     {
+      tree cleanup = NULL_TREE;
+
       /* TARGET_EXPR temps aren't part of the enclosing block, so add it
 	 to the temps list.  Handle also variable length TARGET_EXPRs.  */
       if (TREE_CODE (DECL_SIZE (temp)) != INTEGER_CST)
@@ -5369,8 +5381,30 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 
       /* If needed, push the cleanup for the temp.  */
       if (TARGET_EXPR_CLEANUP (targ))
-	gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ),
-			     CLEANUP_EH_ONLY (targ), pre_p);
+	{
+	  if (CLEANUP_EH_ONLY (targ))
+	    gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ),
+				 CLEANUP_EH_ONLY (targ), pre_p);
+	  else
+	    cleanup = TARGET_EXPR_CLEANUP (targ);
+	}
+
+      /* Add a clobber for the temporary going out of scope, like
+	 gimplify_bind_expr.  */
+      if (needs_to_live_in_memory (temp))
+	{
+	  tree clobber = build_constructor (TREE_TYPE (temp), NULL);
+	  TREE_THIS_VOLATILE (clobber) = true;
+	  clobber = build2 (MODIFY_EXPR, TREE_TYPE (temp), temp, clobber);
+	  if (cleanup)
+	    cleanup = build2 (COMPOUND_EXPR, void_type_node, cleanup,
+			      clobber);
+	  else
+	    cleanup = clobber;
+	}
+
+      if (cleanup)
+	gimple_push_cleanup (temp, cleanup, false, pre_p);
 
       /* Only expand this once.  */
       TREE_OPERAND (targ, 3) = init;
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9f151d1..0582e49 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2011-11-12  Jason Merrill  <jason@redhat.com>
+
+	PR c++/51060
+	* g++.dg/opt/stack2.C: New.
+
 2011-11-12  Uros Bizjak  <ubizjak@gmail.com>
 
 	* lib/gcc-simulate-thread.exp (simulate-thread): Do not run on
diff --git a/gcc/testsuite/g++.dg/opt/stack2.C b/gcc/testsuite/g++.dg/opt/stack2.C
new file mode 100644
index 0000000..8468e1a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/stack2.C
@@ -0,0 +1,33 @@
+// PR c++/51060
+// { dg-options "-Os -Wframe-larger-than=2000 -Werror" }
+
+// Shows a problem of not re-using stack space:
+// Compile as: g++ -c test_stack_reuse.cpp -o /dev/null -Wframe-larger-than=2048 -Werror -Os
+// Result: warning: the frame size of 10240 bytes is larger than 2048 bytes [-Wframe-larger-than=]
+//
+
+struct StackObject
+{
+  StackObject();
+  char buffer[1024];
+};
+
+void Test()
+{
+#define TEST_SUB() \
+  StackObject();
+
+#define TEST() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB() \
+	TEST_SUB()
+
+  TEST()
+}