From 1464a16032e6f4cc16601662eb5d34fbcc9bca21 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Tue, 6 Feb 2018 11:07:08 -0800
Subject: [PATCH] JIT: recognize we have exact type for this in constructors

In constructors the exact type of `this` is known. Tracking this helps the
jit devirtualize calls made from chaining constructors.

Related discussion in #16198.
---
 src/jit/lclvars.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/jit/lclvars.cpp b/src/jit/lclvars.cpp
index bf9a1f9a18f9..1b387999da2f 100644
--- a/src/jit/lclvars.cpp
+++ b/src/jit/lclvars.cpp
@@ -412,8 +412,9 @@ void Compiler::lvaInitThisPtr(InitVarDscInfo* varDscInfo)
         }
         else
         {
-            varDsc->lvType = TYP_REF;
-            lvaSetClass(varDscInfo->varNum, info.compClassHnd);
+            const bool isExact = (info.compFlags & CORINFO_FLG_CONSTRUCTOR) != 0;
+            varDsc->lvType     = TYP_REF;
+            lvaSetClass(varDscInfo->varNum, info.compClassHnd, isExact);
         }
 
         if (tiVerificationNeeded)