Remove __bp__ and speed-up bmethod calls (#8060)

Remove rb_control_frame_t::__bp__ and optimize bmethod calls

This commit removes the __bp__ field from rb_control_frame_t. It was
introduced to help MJIT, but since MJIT was replaced by RJIT, we can use
vm_base_ptr() to compute it from the SP of the previous control frame
instead. Removing the field avoids needing to set it up when pushing new
frames.

Simply removing __bp__ would cause crashes since RJIT and YJIT used a
slightly different stack layout for bmethod calls than the interpreter.
At the moment of the call, the two layouts looked as follows:

                   ┌────────────┐    ┌────────────┐
                   │ frame_base │    │ frame_base │
                   ├────────────┤    ├────────────┤
                   │    ...     │    │    ...     │
                   ├────────────┤    ├────────────┤
                   │    args    │    │    args    │
                   ├────────────┤    └────────────┘<─prev_frame_sp
                   │  receiver  │
    prev_frame_sp─>└────────────┘
                     RJIT & YJIT      interpreter

Essentially, vm_base_ptr() needs to compute the address to frame_base
given prev_frame_sp in the diagrams. The presence of the receiver
created an off-by-one situation.

Make the interpreter use the layout the JITs use for iseq-to-iseq
bmethod calls. Doing so removes unnecessary argument shifting and
vm_exec_core() re-entry from the interpreter, yielding a speed
improvement visible through `benchmark/vm_defined_method.yml`:

     patched:   7578743.1 i/s
      master:   4796596.3 i/s - 1.58x  slower

C-to-iseq bmethod calls now store one more VALUE than before, but that
should have negligible impact on overall performance.

Note that re-entering vm_exec_core() used to be necessary for firing
TracePoint events, but that's no longer the case since
9121e57a5f50bc91bae48b3b91edb283bf96cb6b.

Closes ruby/ruby#6428

1 files changed, 2 insertions, 3 deletions

diff --git a/yjit/src/cruby.rs b/yjit/src/cruby.rs
index 265748cd6d..a3ce30c589 100644
--- a/yjit/src/cruby.rs
+++ b/yjit/src/cruby.rs
@@ -718,9 +718,8 @@ mod manual_defs {
     pub const RUBY_OFFSET_CFP_SELF: i32 = 24;
     pub const RUBY_OFFSET_CFP_EP: i32 = 32;
     pub const RUBY_OFFSET_CFP_BLOCK_CODE: i32 = 40;
-    pub const RUBY_OFFSET_CFP_BP: i32 = 48; // field __bp__
-    pub const RUBY_OFFSET_CFP_JIT_RETURN: i32 = 56;
-    pub const RUBY_SIZEOF_CONTROL_FRAME: usize = 64;
+    pub const RUBY_OFFSET_CFP_JIT_RETURN: i32 = 48;
+    pub const RUBY_SIZEOF_CONTROL_FRAME: usize = 56;
 
     // Constants from rb_execution_context_t vm_core.h
     pub const RUBY_OFFSET_EC_CFP: i32 = 16;