When QuickJit is enabled, disable it for methods that contain loops by default (#24252)

When QuickJit is enabled, disable it for methods that contain loops by default

Fixes https://github.com/dotnet/coreclr/issues/19751 by default when QuickJit is enabled
- Added config variable TC_QuickJitForLoops. When disabled (the default), the JIT identifies loops and explicit tail calls and switches to tier 1 JIT.
- This would prevent the possibility of spending too long in QuickJit code, but may decrease startup time a bit when QuickJit is enabled
- Removed TC_StartupTier_OptimizeCode, as now that there is TC_QuickJit, I didn't see a good use for it
- Removed references to "StartupTier" in config variables because we had previously decided not to call it that.
- When QuickJit is disabled, avoid creating native code slots for methods in non-R2R'ed modules, as tiering would be disabled for those anyway
- Marked TC_QuickJit config var as external

1 files changed, 5 insertions, 0 deletions

diff --git a/src/vm/methodtablebuilder.cpp b/src/vm/methodtablebuilder.cpp
index 5b094f6555..b2e7a07859 100644
--- a/src/vm/methodtablebuilder.cpp
+++ b/src/vm/methodtablebuilder.cpp
@@ -6959,6 +6959,11 @@ MethodTableBuilder::NeedsNativeCodeSlot(bmtMDMethod * pMDMethod)
 #ifdef FEATURE_TIERED_COMPILATION
     // Keep in-sync with MethodDesc::DetermineAndSetIsEligibleForTieredCompilation()
     if (g_pConfig->TieredCompilation() &&
+
+        // Policy - If QuickJit is disabled and the module is not ReadyToRun, the method would be ineligible for tiering
+        // currently to avoid some unnecessary overhead
+        (g_pConfig->TieredCompilation_QuickJit() || GetModule()->IsReadyToRun()) &&
+
         (pMDMethod->GetMethodType() == METHOD_TYPE_NORMAL || pMDMethod->GetMethodType() == METHOD_TYPE_INSTANTIATED))
     {
         return TRUE;