Request for Reviews(M): 7092905: C2: Keep track of the number of dead nodes

[Vladimir Kozlov]

VerifyIdealNodeCount flag should be also notproduct since it is used only in 
debug VM.

The next assert is not needed because it duplicates assert in live_nodes():

     bool check_node_count(uint margin, const char* reason) {
       if (unique() + margin > (uint)MaxNodeLimit) {
+     assert(dead_node_count() <= unique(), "number of dead nodes more than 
created");

Also don't split the assert in live_nodes() into 2 lines and maybe use 
err_msg_res() to print _unique and _dead_node_count values. Also I think it 
should return unsigned int type value as unique() method.

Second Compile() constructor does not set _dead_node_count(0).

count_live_nodes_by_graph_walk() and NotANode() methods are now used only in 
debug code so put them under #ifdef ASSERT.


print_missing_nodes() should call count_live_nodes_by_graph_walk() instead of 
duplicating code. And it should print to _log itself. TracePhase() code will 
have only call to it:

3133   if (VerifyIdealNodeCount) {
3134     Compile::current()->print_missing_nodes();
3135   }

And do not check VerifyIdealNodeCount in print_missing_nodes() to allow call it 
in debugger without VerifyIdealNodeCount set.

I think VerifyIdealNodeCount code should be in ~TracePhase() (end of phase).

Thanks,
Vladimir

Bharadwaj Yadavalli wrote:
> Addressed comments on my previous RFR. Changes 
> at
> http://cr.openjdk.java.net/~bharadwaj/7092905/webrev_02/
> 
> These changes are made to keep an (almost) accurate running count of the 
> reachable (live) flow graph nodes. This will result in a more realistic 
> node count for various phases of C2 to decide on whether to proceed with 
> optimizations or not. Prior to these changes, C2 bails out of 
> compilation based on the number of nodes created which typically larger 
> than the number of reachable (live) nodes.
>