RFR: 8359602: Ideal optimizations depending on input type are missed because of missing notification mechanism from CCP [v3]

[Benoît Maillard]

> This PR prevents some missed ideal optimizations in IGVN by notifying users of type refinements made during CCP, addressing a missed optimization that caused a verification failure with `-XX:VerifyIterativeGVN=1110`.
> 
> ### Context
> During the compilation of the input program (obtained from the fuzzer, then simplified and added as a test) by C2, we end up with node `591 ModI` that takes `138 Phi` as its divisor input. An existing `Ideal` optimization is to get rid of the control input of a `ModINode` when we can prove that the divisor is never `0`.
> 
> In this specific case, the type of the `PhiNode` gets refined during CCP, but the refinement fails to propagate to its users for the IGVN phase and the ideal optimization for the `ModINode` never happens. This results in a missed optimization and hits an assert in the verification phase of IGVN (when using `-XX:VerifyIterativeGVN=1110`).
> 
> ![IGV screenshot](https://github.com/user-attachments/assets/5dee1ae6-9146-4115-922d-df33b7ccbd37)
> 
> ### Detailed Analysis
> 
> In `PhaseCCP::analyze`, we call `Value` for the `PhiNode`, which  
> results in a type refinement: the range gets restricted to `int:-13957..-1191`.
> 
> ```c++
>   // Pull from worklist; compute new value; push changes out.
>   // This loop is the meat of CCP.
>   while (worklist.size() != 0) {
>     Node* n = fetch_next_node(worklist);
>     DEBUG_ONLY(worklist_verify.push(n);)
>     if (n->is_SafePoint()) {
>       // Make sure safepoints are processed by PhaseCCP::transform even if they are
>       // not reachable from the bottom. Otherwise, infinite loops would be removed.
>       _root_and_safepoints.push(n);
>     }
>     const Type* new_type = n->Value(this);
>     if (new_type != type(n)) {
>       DEBUG_ONLY(verify_type(n, new_type, type(n));)
>       dump_type_and_node(n, new_type);
>       set_type(n, new_type);
>       push_child_nodes_to_worklist(worklist, n);
>     }
>     if (KillPathsReachableByDeadTypeNode && n->is_Type() && new_type == Type::TOP) {
>       // Keep track of Type nodes to kill CFG paths that use Type
>       // nodes that become dead.
>       _maybe_top_type_nodes.push(n);
>     }
>   }
>   DEBUG_ONLY(verify_analyze(worklist_verify);)
> 
> 
> At the end of `PhaseCCP::analyze`, we obtain the following types in the side table:
> - `int` for node `591` (`ModINode`)
> - `int:-13957..-1191` for node `138` (`PhiNode`)
> 
> If we call `find_node(138)->bottom_type()`, we get:
> - `int` for both nodes
> 
> There is no progress on the type of `ModINode` during CCP, because `ModINode::Value`  
> is not able to...

Benoît Maillard has updated the pull request incrementally with one additional commit since the last revision:

  Fix bad test class name

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26017/files
  - new: https://git.openjdk.org/jdk/pull/26017/files/e05eb749..75de51df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26017&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26017&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26017.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26017/head:pull/26017

PR: https://git.openjdk.org/jdk/pull/26017