Fix loop-iv.c ICE

Jan Hubicka hubicka@ucw.cz
Wed Jan 16 16:14:00 GMT 2013


Hi,
this patch fixes ICE seen in PR51083 on PPC.  Here the flags ^= 0x80000000 expression
is translated as PLUS.  This makes us to consider flags to be IV and work out that the
loop do not really iterate.   It is a missed optimization that we do not work out this
on all targets and do not unloop the loop at tree level. I opened PR for this.
This patch fixes the ICE that we get confused on concluding that max number of iterations
is 0.

Bootstrapped/regtested x86_64-linux (where the code path do not really trigger obviously)
and tested that it is fixing the testcase on PPC.
OK?

Honza
	PR tree-optimizatoin/51083

	* gcc.c-torture/compile/pr51083.c: New testcase.

	* loop-iv.c (iv_number_of_iterations): Consider zero iteration case.

Index: testsuite/gcc.c-torture/compile/pr51083.c
===================================================================
--- testsuite/gcc.c-torture/compile/pr51083.c	(revision 0)
+++ testsuite/gcc.c-torture/compile/pr51083.c	(revision 0)
@@ -0,0 +1,18 @@
+extern int debug_threads;
+extern void sigsuspend (void);
+void my_waitpid (int flags, int wnohang)
+{
+  while (1)
+    {
+      if (flags & 0x80000000)
+        {
+          if (wnohang)
+            break;
+          if (debug_threads)
+            __builtin_puts ("blocking\n");
+          sigsuspend ();
+        }
+      flags ^= 0x80000000;
+    }
+}
+
Index: loop-iv.c
===================================================================
--- loop-iv.c	(revision 195144)
+++ loop-iv.c	(working copy)
@@ -2819,7 +2819,8 @@ iv_number_of_iterations (struct loop *lo
   else
     {
       max = determine_max_iter (loop, desc, old_niter);
-      gcc_assert (max);
+      if (!max)
+	goto zero_iter_simplify;
       if (!desc->infinite
 	  && !desc->assumptions)
 	record_niter_bound (loop, double_int::from_uhwi (max),



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