From 60d00c47a69a6054ff82bec717cfc5a2d6ff23c6 Mon Sep 17 00:00:00 2001
From: Egor Bogatov <egorbo@gmail.com>
Date: Mon, 5 Dec 2022 16:46:03 +0100
Subject: [PATCH] Intrinsify Interlocked.CompareExchange and
 Interlocked.Exchange for null (#79181)

---
 .../src/System/Threading/Interlocked.CoreCLR.cs   |  2 ++
 src/coreclr/jit/codegenxarch.cpp                  |  2 +-
 src/coreclr/jit/emitxarch.cpp                     |  9 ++++++++-
 src/coreclr/jit/importercalls.cpp                 | 15 +++++++++++++--
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/coreclr/System.Private.CoreLib/src/System/Threading/Interlocked.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/Threading/Interlocked.CoreCLR.cs
index a4ab35444ae7..2e683dcf73c8 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/Threading/Interlocked.CoreCLR.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/Threading/Interlocked.CoreCLR.cs
@@ -81,6 +81,7 @@ public static partial class Interlocked
         /// <param name="value">The value to which the <paramref name="location1"/> parameter is set.</param>
         /// <returns>The original value of <paramref name="location1"/>.</returns>
         /// <exception cref="NullReferenceException">The address of location1 is a null pointer.</exception>
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         [return: NotNullIfNotNull(nameof(location1))]
         public static extern object? Exchange([NotNullIfNotNull(nameof(value))] ref object? location1, object? value);
@@ -145,6 +146,7 @@ public static partial class Interlocked
         /// <param name="comparand">The object that is compared by reference to the object at <paramref name="location1"/>.</param>
         /// <returns>The original value in <paramref name="location1"/>.</returns>
         /// <exception cref="NullReferenceException">The address of <paramref name="location1"/> is a null pointer.</exception>
+        [Intrinsic]
         [MethodImpl(MethodImplOptions.InternalCall)]
         [return: NotNullIfNotNull(nameof(location1))]
         public static extern object? CompareExchange(ref object? location1, object? value, object? comparand);
diff --git a/src/coreclr/jit/codegenxarch.cpp b/src/coreclr/jit/codegenxarch.cpp
index 3adde7d491ac..ec9268597492 100644
--- a/src/coreclr/jit/codegenxarch.cpp
+++ b/src/coreclr/jit/codegenxarch.cpp
@@ -4064,7 +4064,7 @@ void CodeGen::genLockedInstructions(GenTreeOp* node)
 
     assert(addr->isUsedFromReg());
     assert(data->isUsedFromReg());
-    assert((size == EA_4BYTE) || (size == EA_PTRSIZE));
+    assert((size == EA_4BYTE) || (size == EA_PTRSIZE) || (size == EA_GCREF));
 
     genConsumeOperands(node);
 
diff --git a/src/coreclr/jit/emitxarch.cpp b/src/coreclr/jit/emitxarch.cpp
index a0008218ecf6..1c3c3bffd90a 100644
--- a/src/coreclr/jit/emitxarch.cpp
+++ b/src/coreclr/jit/emitxarch.cpp
@@ -12193,7 +12193,14 @@ BYTE* emitter::emitOutputAM(BYTE* dst, instrDesc* id, code_t code, CnsVal* addc)
 
             case IF_ARW_RRD:
             case IF_ARW_CNS:
-                assert(id->idGCref() == GCT_BYREF && (ins == INS_add || ins == INS_sub || ins == INS_sub_hide));
+                if (id->idGCref() == GCT_BYREF)
+                {
+                    assert(ins == INS_add || ins == INS_sub || ins == INS_sub_hide);
+                }
+                else
+                {
+                    assert((id->idGCref() == GCT_GCREF) && (ins == INS_cmpxchg || ins == INS_xchg));
+                }
                 break;
 
             default:
diff --git a/src/coreclr/jit/importercalls.cpp b/src/coreclr/jit/importercalls.cpp
index 90163e6f842f..3504e04d5025 100644
--- a/src/coreclr/jit/importercalls.cpp
+++ b/src/coreclr/jit/importercalls.cpp
@@ -2967,7 +2967,12 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
                 {
                     break;
                 }
-                if ((retType != TYP_INT) && (retType != TYP_LONG))
+                if ((retType == TYP_REF) && impStackTop(1).val->IsIntegralConst(0))
+                {
+                    // Intrinsify "object" overload in case of null assignment
+                    // since we don't need the write barrier.
+                }
+                else if ((retType != TYP_INT) && (retType != TYP_LONG))
                 {
                     break;
                 }
@@ -2997,7 +3002,13 @@ GenTree* Compiler::impIntrinsic(GenTree*                newobjThis,
                 {
                     break;
                 }
-                if ((retType != TYP_INT) && (retType != TYP_LONG))
+                if ((retType == TYP_REF) && impStackTop().val->IsIntegralConst(0))
+                {
+                    // Intrinsify "object" overload in case of null assignment
+                    // since we don't need the write barrier.
+                    assert(ni == NI_System_Threading_Interlocked_Exchange);
+                }
+                else if ((retType != TYP_INT) && (retType != TYP_LONG))
                 {
                     break;
                 }