From 218a90ec735ba9a1c1e015c163a03c9377997e27 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Tue, 28 Jul 2020 09:26:43 -0700
Subject: [PATCH] JIT: ensure fgFirstBB has appropriate flags

This fixes an issue where release jits might sometimes generate bad GC info.
Keeping it minimal for now so we can consider servicing preview 8.

See #39023 for details.
---
 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 65c9af9e8f2c7a..524fce6d4e5d5d 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;