Re: [PATCH] Fix -fcompare-debug due to DEBUG_BEGIN_STMTs (PR debug/83419)

[Alexandre Oliva <aoliva at redhat dot com>]

On Dec 21, 2017, Jakub Jelinek <jakub@redhat.com> wrote:

> On Wed, Dec 20, 2017 at 10:02:24PM -0200, Alexandre Oliva wrote:
>> +	  if (tsi_one_before_end_p (i))
>> +	    TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (tsi_stmt (i));

> So DEBUG_BEGIN_STMTs after the single non-DEBUG_BEGIN_STMT stmt in
> the STATEMENT_LIST can't happen (or just we don't have a testcase for it)?

I know I said it couldn't, but while looking into PR83527 I decided to
actually check that, and my conclusion quickly proved to be false.  So
the patch below fixes that, as well as the newer PR.

This has completed -fcompare-debug bootstrap on i686- and
ppc64le-linux-gnu; x86_64-linux-gnu is almost done, and regression
testing for them all is underway or about to start.  Ok to install if it
all passes?


for  gcc/c-family/ChangeLog

	PR debug/83527
	PR debug/83419
	* c-semantics.c (only_debug_stmts_after_p): New.
	(pop_stmt_list): Clear side effects in debug-only stmt list.
	Check for single nondebug stmt followed by debug stmts only.

for  gcc/testsuite/ChangeLog

	PR debug/83527
	PR debug/83419
	* gcc.dg/pr83527.c: New.
---
 gcc/c-family/c-semantics.c     |   23 +++++++++++++++++++----
 gcc/testsuite/gcc.dg/pr83527.c |   26 ++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr83527.c

diff --git a/gcc/c-family/c-semantics.c b/gcc/c-family/c-semantics.c
index 3a972c32c8ea..21d908ed06c1 100644
--- a/gcc/c-family/c-semantics.c
+++ b/gcc/c-family/c-semantics.c
@@ -35,6 +35,17 @@ push_stmt_list (void)
   return t;
 }
 
+/* Return TRUE if, after I, there are any nondebug stmts.  */
+
+static inline bool
+only_debug_stmts_after_p (tree_stmt_iterator i)
+{
+  for (tsi_next (&i); !tsi_end_p (i); tsi_next (&i))
+    if (TREE_CODE (tsi_stmt (i)) != DEBUG_BEGIN_STMT)
+      return false;
+  return true;
+}
+
 /* Finish the statement tree rooted at T.  */
 
 tree
@@ -99,11 +110,15 @@ pop_stmt_list (tree t)
 	  while (!tsi_end_p (i)
 		 && TREE_CODE (tsi_stmt (i)) == DEBUG_BEGIN_STMT)
 	    tsi_next (&i);
-	  /* If there's only one nondebug stmt in the list, we'd have
-	     extracted the stmt and dropped the list, and we'd take
-	     TREE_SIDE_EFFECTS from that statement, so keep the list's
+	  /* If there are only debug stmts in the list, without them
+	     we'd have an empty stmt without side effects.  If there's
+	     only one nondebug stmt, we'd have extracted the stmt and
+	     dropped the list, and we'd take TREE_SIDE_EFFECTS from
+	     that statement.  In either case, keep the list's
 	     TREE_SIDE_EFFECTS in sync.  */
-	  if (tsi_one_before_end_p (i))
+	  if (tsi_end_p (i))
+	    TREE_SIDE_EFFECTS (t) = 0;
+	  else if (only_debug_stmts_after_p (i))
 	    TREE_SIDE_EFFECTS (t) = TREE_SIDE_EFFECTS (tsi_stmt (i));
 	}
     }
diff --git a/gcc/testsuite/gcc.dg/pr83527.c b/gcc/testsuite/gcc.dg/pr83527.c
new file mode 100644
index 000000000000..effef439ac07
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr83527.c
@@ -0,0 +1,26 @@
+/* PR debug/83527 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcompare-debug" } */
+
+extern void fn2(void);
+extern void fn3(void);
+int a, b;
+void fn1() {
+  int c;
+  short d;
+  switch (a) {
+  case 32800:
+    fn2();
+  case 32769:
+    b = 0;
+  case 32771:
+  case 32772:
+  case 32782:
+    fn3();
+  }
+  if (d || c) {
+    do
+      ;
+    while (0);
+  }
+}


-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer