According to stats and profiling only about 40% of bytecode instructions are executed by tier 2 and the remaining 60% by tier 1.

We the expected improvements to the JIT and tier 2 optimizer we expect tier 2 (with JIT) to have a significantly faster than tier 1.
It therefore make sense to get the fraction of instructions executed by tier 2 up from 40% to nearer 90%.

To do that we need to:

• Enter tier 2 at some function entry points as well as back edges. #118094
• Stay in tier 2 when exiting executors in most cases Trace stitching #112354
• Increase the number of micro-ops that we can handle in tier 2 #118095

Linked PRs

• GH-118093: Add tier two support to several instructions #121884
• GH-118093: Remove invalidated executors from side exits #121885
• GH-118093: Better handling of short and mid-loop traces #122252
• GH-118093: Add tier two support for BINARY_OP_INPLACE_ADD_UNICODE #122253
• GH-118093: Add tier two support for LOAD_ATTR_PROPERTY #122283
• GH-118093: Handle some polymorphism before requiring progress in tier two #122843
• GH-118093: Turn some DEOPT_IFs into EXIT_IFs #122998
• GH-118093: Specialize CALL_KW #123006
• GH-118093: Specialize CALL_FUNCTION_EX #123034
• GH-118093: Make CALL_ALLOC_AND_ENTER_INIT suitable for tier 2. #123140
• GH-118093: Specialize calls to non-vectorcall classes as CALL_NON_PY_GENERAL #123212
• GH-118093: Fix off-by-one errors in tier-up thresholds #124447
• GH-118093: Don't lose confidence when tracing through 100% biased branches #124813