[NFC][Support] Eliminate ',' at end of MemoryEffects print

- Eliminate comma at end of a MemoryEffects print.
- Added basic unit test to validate that.

llvm/lib/Support/ModRef.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/ModRef.h"
+#include "llvm/ADT/STLExtras.h"
 
 using namespace llvm;
 
@@ -33,7 +34,7 @@ raw_ostream &llvm::operator<<(raw_ostream &OS, ModRefInfo MR) {
 }
 
 raw_ostream &llvm::operator<<(raw_ostream &OS, MemoryEffects ME) {
-  for (IRMemLocation Loc : MemoryEffects::locations()) {
+  interleaveComma(MemoryEffects::locations(), OS, [&](IRMemLocation Loc) {
     switch (Loc) {
     case IRMemLocation::ArgMem:
       OS << "ArgMem: ";
@@ -45,7 +46,7 @@ raw_ostream &llvm::operator<<(raw_ostream &OS, MemoryEffects ME) {
       OS << "Other: ";
       break;
     }
-    OS << ME.getModRef(Loc) << ", ";
-  }
+    OS << ME.getModRef(Loc);
+  });
   return OS;
 }

llvm/unittests/Support/CMakeLists.txt

@@ -61,6 +61,7 @@ add_llvm_unittest(SupportTests
   MemoryBufferRefTest.cpp
   MemoryBufferTest.cpp
   MemoryTest.cpp
+  ModRefTest.cpp
   NativeFormatTests.cpp
   OptimizedStructLayoutTest.cpp
   ParallelTest.cpp

llvm/unittests/Support/ModRefTest.cpp

@@ -0,0 +1,28 @@
+//===- llvm/unittest/Support/ModRefTest.cpp - ModRef tests ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/ModRef.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/raw_ostream.h"
+#include "gtest/gtest.h"
+#include <string>
+
+using namespace llvm;
+
+namespace {
+
+// Verify that printing a MemoryEffects does not end with a ,.
+TEST(ModRefTest, PrintMemoryEffects) {
+  std::string S;
+  raw_string_ostream OS(S);
+  OS << MemoryEffects::none();
+  OS.flush();
+  EXPECT_EQ(S, "ArgMem: NoModRef, InaccessibleMem: NoModRef, Other: NoModRef");
+}
+
+} // namespace