[trans-mem] random segfault

[Aldy Hernandez]

> Hi Aldy,
>
> I was trying to compile almost the same code and gcc is going into a  
> stack overflow (infinite call).
>
> Here the testcase (gcc -fgnu-tm -Wall -O1 -o common.o -c common.c):
> __attribute__((transaction_safe))
> void Info_RemoveKey (char *s)
> {
>         char    *o = 0;
>         while (1)
>         {
>                 s++;
>                 while (*s)
>                 {
>                         if (!*s)
>                                 return;
>                         *o++ = *s++;
>                 }
>                 *o = 0;
>         }
> }

thread_private_new_memory() is recursing on itself when the web of PHI
nodes has a mutual dependency (albeit with SSA variables originating
from different basic blocks).

Fixed by making sure we're not recursing on the same variable.

OK for branch?

	* trans-mem.c (thread_private_new_memory): Avoid infinite recursion.

Index: testsuite/gcc.dg/tm/20100615-2.c
===================================================================
--- testsuite/gcc.dg/tm/20100615-2.c	(revision 0)
+++ testsuite/gcc.dg/tm/20100615-2.c	(revision 0)
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-fgnu-tm -O" } */
+
+__attribute__((transaction_safe))
+void Info_RemoveKey (char *s)
+{
+        char    *o = 0;
+        while (1)
+        {
+                s++;
+                while (*s)
+                {
+                        if (!*s)
+                                return;
+                        *o++ = *s++;
+                }
+                *o = 0;
+        }
+}
Index: trans-mem.c
===================================================================
--- trans-mem.c	(revision 160765)
+++ trans-mem.c	(working copy)
@@ -1331,6 +1331,10 @@ thread_private_new_memory (basic_block e
 		  if (phi_result == op)
 		    continue;
 
+		  /* Ignore self-recursion in calculation.  */
+		  if (val == op)
+		    continue;
+
 		  mem = thread_private_new_memory (entry_block, op);
 		  if (mem == mem_non_local)
 		    {