From dfccb3ffb4eaed1ab3b13ea74186ec7d7b4ccf9f Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Wed, 29 Jul 2020 09:07:23 -0700
Subject: [PATCH] Port JIT fix to Preview 8: ensure fgFirstBB has appropriate
 flags

Port of #40038 to Preview 8.

Fix #39023

Release jits might sometimes generate bad GC info.

Mysterious intermittent crashes. Without this fix jit GC
info generation for some methods is non-deterministically bad.

Yes, problem does not occur in 3.1.

Very low.
---
 src/coreclr/src/jit/flowgraph.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/coreclr/src/jit/flowgraph.cpp b/src/coreclr/src/jit/flowgraph.cpp
index ab39e2c25d232..6dd724bf1828e 100644
--- a/src/coreclr/src/jit/flowgraph.cpp
+++ b/src/coreclr/src/jit/flowgraph.cpp
@@ -175,6 +175,8 @@ void Compiler::fgInit()
 #ifdef FEATURE_SIMD
     fgPreviousCandidateSIMDFieldAsgStmt = nullptr;
 #endif
+
+    fgHasSwitch = false;
 }
 
 bool Compiler::fgHaveProfileData()
@@ -476,7 +478,8 @@ void Compiler::fgEnsureFirstBBisScratch()
 
     noway_assert(fgLastBB != nullptr);
 
-    block->bbFlags |= (BBF_INTERNAL | BBF_IMPORTED);
+    // Set the expected flags
+    block->bbFlags |= (BBF_INTERNAL | BBF_IMPORTED | BBF_JMP_TARGET | BBF_HAS_LABEL);
 
     // This new first BB has an implicit ref, and no others.
     block->bbRefs = 1;