On 13.12.2021 18:20, Alexander Monakov wrote:
> On Mon, 13 Dec 2021, Richard Biener wrote:
>
>> On December 13, 2021 3:25:47 PM GMT+01:00, Alexander Monakov <amonakov@ispras.ru> wrote:
>>> Greetings!
>>>
>>> While testing our patch that reimplements -Wclobbered on GIMPLE we found
>>> a case where tree-ssa-sink moves a statement to a basic block in front
>>> of a setjmp call.
>>>
>>> I am confident that this is unintended and should be considered invalid
>>> GIMPLE.
>> Does CFG validation not catch this? That is, doesn't setjmp force the start of
>> a new BB?
> Oh, good point. There's stmt_start_bb_p which returns true for setjmp, but
> gimple_verify_flow_info doesn't check it. I guess we can try adding that
> and collect the fallout on bootstrap/regtest.

Bootstrap looks good, but testsuite has some regression (the applied 
patch is below).

The overall number of unexpected failures and unresolved testcases is 
around 100. The diff is in attachment.
>> I think sinking relies on dominance and post dominance here but post dominance
>> may be too fragile with the abnormal cycles which are likely not backwards
>> reachable from exit.
>>
>> That said, checking for abnormal preds is OK, I just want to make sure we
>> detect the invalid CFG - do we?
> As above, no, otherwise it would have been caught much earlier than ICE'ing
> our -Wclobbered patch :)
>
> Thank you.
> Alexander

The patch for CFG validation:

diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index ebbd894ae03..92b08d1d6d8 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -5663,6 +5663,7 @@ gimple_verify_flow_info (void)
         }

        /* Verify that body of basic block BB is free of control flow.  */
+      gimple *prev_stmt = NULL;
        for (; !gsi_end_p (gsi); gsi_next (&gsi))
         {
           gimple *stmt = gsi_stmt (gsi);
@@ -5674,6 +5675,14 @@ gimple_verify_flow_info (void)
               err = 1;
             }

+         if (prev_stmt && stmt_starts_bb_p (stmt, prev_stmt))
+           {
+             error ("setjmp in the middle of basic block %d", bb->index);
+             err = 1;
+           }
+         if (!is_gimple_debug (stmt))
+           prev_stmt = stmt;
+
           if (stmt_ends_bb_p (stmt))
             found_ctrl_stmt = true;