RFR: 8144484: assert(no_dead_loop) failed: dead loop detected

[Vladimir Kozlov]

Sorry, I don't like this fix.

Based on your evaluation one control path is dead (top) and it will be optimized out later. It was unfortunate that Phi 
node was processed first. Change graph (split through MergeMem) is dangerous in this state of graph.

I would suggest to bailout early:

1886   if (progress == NULL && can_reshape && type() == Type::MEMORY) {
1887     // see if this phi should be sliced
1888     uint merge_width = 0;
1889     bool saw_self = false;
1890     for( uint i=1; i<req(); ++i ) {// For all paths in
1891       Node *ii = in(i);

+          // TOP inputs should not be counted as safe inputs because if the
+          // Phi references itself through all other inputs then splitting the
+          // Phi through memory merges would create dead loop at later stage.
+          if (ii == top) {
+            return top; // Delay optimization until graph is cleaned.
+          }

1892       if (ii->is_MergeMem()) {
1893         MergeMemNode* n = ii->as_MergeMem();

Thanks,
Vladimir

On 1/31/17 11:38 PM, Tobias Hartmann wrote:
> Hi Rahul,
>
> On 31.01.2017 19:55, Rahul Raghavan wrote:
>> Please see updated <webrev.01> -
>> http://cr.openjdk.java.net/~rraghavan/8144484/webrev.01/
>
> Looks good to me!
>
> Best regards,
> Tobias
>