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Re: allow EH to escape from GIMPLE_EH_ELSE ELSE block


... and here's a patch that uses a try/finally/else gimplefe test to
demonstrate the GIMPLE_EH_ELSE lowering problem (might_throw3 is tagged
as [LP 1] rather than [LP 2]), and fixes it.

Regstrapped on x86_64-linux-gnu.  Ok to install?


allow EH to escape from GIMPLE_EH_ELSE ELSE block

The only preexisting use of GIMPLE_EH_ELSE, for transactional memory
commits, did not allow exceptions to escape from the ELSE path.  The
trick it uses to allow the ELSE path to see the propagating exception
does not work very well if the exception cleanup raises further
exceptions: the ELSE block is configured to handle exceptions in
itself.  This confuses the heck out of CFG and EH cleanups.

Basing the lowering context for the ELSE block on outer_state, rather
than this_state, gets us the expected enclosing handler.


for  gcc/ChangeLog

	* tree-eh.c (honor_protect_cleanup_actions): Use outer_
	rather than this_state as the lowering context for the ELSE
	seq in a GIMPLE_EH_ELSE.

for  gcc/testsuite/ChangeLog

	* gcc.dg/gimplefe-44.c: New.
---
 gcc/testsuite/gcc.dg/gimplefe-44.c |   33 +++++++++++++++++++++++++++++++++
 gcc/tree-eh.c                      |   13 ++++++++-----
 2 files changed, 41 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/gimplefe-44.c

diff --git a/gcc/testsuite/gcc.dg/gimplefe-44.c b/gcc/testsuite/gcc.dg/gimplefe-44.c
new file mode 100644
index 000000000000..a9a92b1701ec
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/gimplefe-44.c
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-fexceptions -fgimple -fdump-tree-eh-eh" } */
+
+void __GIMPLE foo()
+{
+  try
+    {
+      try
+	{
+	  extern void might_throw1 ();
+	  might_throw1 ();
+	}
+      finally
+	{
+	  extern void might_throw2 ();
+	  might_throw2 ();
+	}
+      else
+	{
+	  extern void might_throw3 ();
+	  might_throw3 ();
+	}
+    }
+  finally
+    {
+      extern void might_throw4 ();
+      might_throw4 ();
+    }
+}
+
+/* { dg-final { scan-tree-dump ".LP 1. might_throw1" "eh" } } */
+/* { dg-final { scan-tree-dump ".LP 2. might_throw2" "eh" } } */
+/* { dg-final { scan-tree-dump ".LP 2. might_throw3" "eh" } } */
diff --git a/gcc/tree-eh.c b/gcc/tree-eh.c
index fb7d202fc6f9..5bb07e49d285 100644
--- a/gcc/tree-eh.c
+++ b/gcc/tree-eh.c
@@ -996,11 +996,14 @@ honor_protect_cleanup_actions (struct leh_state *outer_state,
       gimple_try_set_cleanup (tf->top_p, gimple_eh_else_n_body (eh_else));
       finally = gimple_eh_else_e_body (eh_else);
 
-      /* Let the ELSE see the exception that's being processed.  */
-      eh_region save_ehp = this_state->ehp_region;
-      this_state->ehp_region = this_state->cur_region;
-      lower_eh_constructs_1 (this_state, &finally);
-      this_state->ehp_region = save_ehp;
+      /* Let the ELSE see the exception that's being processed, but
+	 since the cleanup is outside the try block, process it with
+	 outer_state, otherwise it may be used as a cleanup for
+	 itself, and Bad Things (TM) ensue.  */
+      eh_region save_ehp = outer_state->ehp_region;
+      outer_state->ehp_region = this_state->cur_region;
+      lower_eh_constructs_1 (outer_state, &finally);
+      outer_state->ehp_region = save_ehp;
     }
   else
     {


-- 
Alexandre Oliva, freedom fighter  he/him   https://FSFLA.org/blogs/lxo
Be the change, be Free!                 FSF Latin America board member
GNU Toolchain Engineer                        Free Software Evangelist
Hay que enGNUrecerse, pero sin perder la terGNUra jamás - Che GNUevara


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