Enable tiered jitting for R2R methods (#15967)

Enable tiered jitting for R2R methods

- Included R2R methods and generics over value types in CoreLib for tiered jitting. Tier 0 for R2R methods is the precompiled code if available, and tier 1 is selectively scheduled based on call counting.
- Added a delay before starting to count calls for tier 1 promotion. The delay is a short duration after frequent tier 0 jitting stops (current heuristic for identifying startup).
- Startup time and steady-state performance have improved on JitBench. There is a regression shortly following startup due to call counting and tier 1 jitting, for a short duration before steady-state performance stabilizes.
- Added two new config values, one for configuring the call count threshold for promoting to tier 1, and another for specifying the delay from the last tier 0 JIT invocation before starting to count calls

1 files changed, 27 insertions, 0 deletions

diff --git a/src/vm/arm64/cgencpu.h b/src/vm/arm64/cgencpu.h
index a168cdc162..7e3d62056a 100644
--- a/src/vm/arm64/cgencpu.h
+++ b/src/vm/arm64/cgencpu.h
@@ -24,6 +24,7 @@ EXTERN_C void setFPReturn(int fpSize, INT64 retVal);
 
 class ComCallMethodDesc;
 
+extern PCODE GetPreStubEntryPoint();
 
 #define COMMETHOD_PREPAD                        24   // # extra bytes to allocate in addition to sizeof(ComCallMethodDesc)
 #ifdef FEATURE_COMINTEROP
@@ -572,6 +573,19 @@ struct StubPrecode {
         return m_pTarget;
     }
 
+    void ResetTargetInterlocked()
+    {
+        CONTRACTL
+        {
+            THROWS;
+            GC_TRIGGERS;
+        }
+        CONTRACTL_END;
+
+        EnsureWritableExecutablePages(&m_pTarget);
+        InterlockedExchange64((LONGLONG*)&m_pTarget, (TADDR)GetPreStubEntryPoint());
+    }
+
     BOOL SetTargetInterlocked(TADDR target, TADDR expected)
     {
         CONTRACTL
@@ -685,6 +699,19 @@ struct FixupPrecode {
         return m_pTarget;
     }
 
+    void ResetTargetInterlocked()
+    {
+        CONTRACTL
+        {
+            THROWS;
+            GC_TRIGGERS;
+        }
+        CONTRACTL_END;
+
+        EnsureWritableExecutablePages(&m_pTarget);
+        InterlockedExchange64((LONGLONG*)&m_pTarget, (TADDR)GetEEFuncEntryPoint(PrecodeFixupThunk));
+    }
+
     BOOL SetTargetInterlocked(TADDR target, TADDR expected)
     {
         CONTRACTL