From 4ae47a247208abc28c0077705110774a89a088f5 Mon Sep 17 00:00:00 2001
From: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Date: Wed, 5 Apr 2023 14:32:38 +0200
Subject: [PATCH] JIT: Avoid unnecessary GTF_GLOB_REFs

* Avoid setting GTF_GLOB_REF on GT_FIELD_ADDR nodes
* Avoid setting GTF_GLOB_REF on GT_FIELD nodes off of implicit byrefs.
  This is ok now since implicit byref morphing indiscriminately sets
  GTF_GLOB_REF for these.

These changes are necessary to avoid address exposure in the two user
benchmarks in #83388.

Fix #74563
---
 src/coreclr/jit/gentree.cpp  | 24 +-----------------------
 src/coreclr/jit/importer.cpp |  4 +---
 2 files changed, 2 insertions(+), 26 deletions(-)

diff --git a/src/coreclr/jit/gentree.cpp b/src/coreclr/jit/gentree.cpp
index a1d3fdb805630..518edb0918f2e 100644
--- a/src/coreclr/jit/gentree.cpp
+++ b/src/coreclr/jit/gentree.cpp
@@ -7714,16 +7714,6 @@ GenTreeField* Compiler::gtNewFieldRef(var_types type, CORINFO_FIELD_HANDLE fldHn
         LclVarDsc* varDsc = lvaGetDesc(obj->AsLclVarCommon());
 
         varDsc->lvFieldAccessed = 1;
-
-        if (lvaIsImplicitByRefLocal(lvaGetLclNum(varDsc)))
-        {
-            // These structs are passed by reference and can easily become global references if those
-            // references are exposed. We clear out address-exposure information for these parameters
-            // when they are converted into references in fgRetypeImplicitByRefArgs() so we do not have
-            // the necessary information in morph to know if these indirections are actually global
-            // references, so we have to be conservative here.
-            fieldNode->gtFlags |= GTF_GLOB_REF;
-        }
     }
     else
     {
@@ -7758,20 +7748,8 @@ GenTreeField* Compiler::gtNewFieldAddrNode(var_types type, CORINFO_FIELD_HANDLE
     // If "obj" is the address of a local, note that a field of that struct local has been accessed.
     if ((obj != nullptr) && obj->IsLclVarAddr())
     {
-        LclVarDsc* varDsc = lvaGetDesc(obj->AsLclVarCommon());
-
+        LclVarDsc* varDsc       = lvaGetDesc(obj->AsLclVarCommon());
         varDsc->lvFieldAccessed = 1;
-
-        if (lvaIsImplicitByRefLocal(lvaGetLclNum(varDsc)))
-        {
-            // TODO-ADDR: delete this zero-diff quirk.
-            fieldNode->gtFlags |= GTF_GLOB_REF;
-        }
-    }
-    else
-    {
-        // TODO-ADDR: delete this zero-diff quirk.
-        fieldNode->gtFlags |= GTF_GLOB_REF;
     }
 
     // TODO-ADDR: add GTF_EXCEPT handling here and delete it from callers.
diff --git a/src/coreclr/jit/importer.cpp b/src/coreclr/jit/importer.cpp
index 8e4365023b357..2ed77627fe412 100644
--- a/src/coreclr/jit/importer.cpp
+++ b/src/coreclr/jit/importer.cpp
@@ -8397,9 +8397,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
                     }
                     else if (op1->TypeIs(TYP_BYREF, TYP_I_IMPL) && impIsAddressInLocal(op1))
                     {
-                        // We mark implicit byrefs with GTF_GLOB_REF (see gtNewFieldRef for why).
-                        // Avoid cloning for these.
-                        clone = (op1->gtFlags & GTF_GLOB_REF) == 0;
+                        clone = true;
                     }
 
                     if (clone)