RFR(S): Remove faulty assertion in Compile::call_generator triggered with -XX:+AlwaysIncrementalInline

[Ludovic Henry]

Hi,

While playing with -XX:+AlwaysIncrementalInline, I ran into an assertion triggering on pretty much any tests in test/hotspot/jtreg in debug (slow or fast, assertion just need to be enabled). I tracked it down to the following issue and explanation.

In CallGenerator, when calling `for_method_handle_call`, it will redirect to one of the following:
- `for_method_handle_inline` itself redirecting to `Compile::call_generator`
- `for_late_inline`
- `for_mh_late_inline`
- `for_direct_call`

The removed assert would fail if we end up calling `for_late_inline`. That would be the case when `for_method_handle_inline` returns successfully and AlwaysIncrementalInline is set. This would guarantee failure whenever this global setting is set with -XX:+AlwaysIncrementalInline

In this case, we can safely remove the assert because the case treated specificically in `for_mh_late_inline` is treated by the combination of `for_method_handle_inline` and `for_late_inline`.

Looking at `LateInlineMHCallGenerator::do_late_inline_check`, which is called from `LateInlineCallGenerator::do_late_inline`, we notice that it itself calls `for_method_handle_inline`. This means that `for_method_handle_inline` is called through the two following path with late inlining:
1. `for_late_inline` -> `do_late_inline` <- `for_method_handle_inline` (which was previously called and its result passed through `for_late_inline(inline_cg)`)
2. `for_late_mh_inline` -> `do_late_inline` -> `do_late_inline_check` -> `for_method_handle_inline`

So whether we return a LateInlineCallGenerator or a LateInlineMHCallGenerator from `for_method_handle_call`, the logic in `for_method_handle_inline` will be called.

I do not have authorship status, so I can neither create a JBS nor a webrev. I am working with a colleague to do it, and I'll link it here, but feel free to create any of it before that. The diff is available at [1]

Thank you,

--
Ludovic

[1]
diff --git a/src/hotspot/share/opto/doCall.cpp b/src/hotspot/share/opto/doCall.cpp
index c4d55d0d4c4..ba5f737592e 100644
--- a/src/hotspot/share/opto/doCall.cpp
+++ b/src/hotspot/share/opto/doCall.cpp
@@ -146,7 +146,6 @@ CallGenerator* Compile::call_generator(ciMethod* callee, int vtable_index, bool
   // have bytecodes and so normal inlining fails.
   if (callee->is_method_handle_intrinsic()) {
     CallGenerator* cg = CallGenerator::for_method_handle_call(jvms, caller, callee);
-    assert(cg == NULL || !cg->is_late_inline() || cg->is_mh_late_inline(), "unexpected CallGenerator");
     return cg;
   }