diff --git a/llvm/include/llvm/ADT/StringExtras.h b/llvm/include/llvm/ADT/StringExtras.h
index 7d81c63485be2..2440e7678a831 100644
--- a/llvm/include/llvm/ADT/StringExtras.h
+++ b/llvm/include/llvm/ADT/StringExtras.h
@@ -529,13 +529,15 @@ inline std::string join_items(Sep Separator, Args &&... Items) {
 class ListSeparator {
   bool First = true;
   StringRef Separator;
+  StringRef Prefix;
 
 public:
-  ListSeparator(StringRef Separator = ", ") : Separator(Separator) {}
+  ListSeparator(StringRef Separator = ", ", StringRef Prefix = "")
+      : Separator(Separator), Prefix(Prefix) {}
   operator StringRef() {
     if (First) {
       First = false;
-      return {};
+      return Prefix;
     }
     return Separator;
   }
diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
index bf8a6cdf097a9..368aab73498ec 100644
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -866,48 +866,46 @@ static void printMI(raw_ostream &OS, MFPrintState &State,
 
   OS << TII->getName(MI.getOpcode());
 
-  LS = ListSeparator();
+  // Print a space after the opcode if any additional tokens are printed.
+  LS = ListSeparator(", ", " ");
 
-  if (I < E) {
-    OS << ' ';
-    for (; I < E; ++I) {
-      OS << LS;
-      printMIOperand(OS, State, MI, I, TRI, TII, ShouldPrintRegisterTies,
-                     PrintedTypes, MRI, /*PrintDef=*/true);
-    }
+  for (; I < E; ++I) {
+    OS << LS;
+    printMIOperand(OS, State, MI, I, TRI, TII, ShouldPrintRegisterTies,
+                   PrintedTypes, MRI, /*PrintDef=*/true);
   }
 
   // Print any optional symbols attached to this instruction as-if they were
   // operands.
   if (MCSymbol *PreInstrSymbol = MI.getPreInstrSymbol()) {
-    OS << LS << " pre-instr-symbol ";
+    OS << LS << "pre-instr-symbol ";
     MachineOperand::printSymbol(OS, *PreInstrSymbol);
   }
   if (MCSymbol *PostInstrSymbol = MI.getPostInstrSymbol()) {
-    OS << LS << " post-instr-symbol ";
+    OS << LS << "post-instr-symbol ";
     MachineOperand::printSymbol(OS, *PostInstrSymbol);
   }
   if (MDNode *HeapAllocMarker = MI.getHeapAllocMarker()) {
-    OS << LS << " heap-alloc-marker ";
+    OS << LS << "heap-alloc-marker ";
     HeapAllocMarker->printAsOperand(OS, State.MST);
   }
   if (MDNode *PCSections = MI.getPCSections()) {
-    OS << LS << " pcsections ";
+    OS << LS << "pcsections ";
     PCSections->printAsOperand(OS, State.MST);
   }
   if (MDNode *MMRA = MI.getMMRAMetadata()) {
-    OS << LS << " mmra ";
+    OS << LS << "mmra ";
     MMRA->printAsOperand(OS, State.MST);
   }
   if (uint32_t CFIType = MI.getCFIType())
-    OS << LS << " cfi-type " << CFIType;
+    OS << LS << "cfi-type " << CFIType;
 
   if (auto Num = MI.peekDebugInstrNum())
-    OS << LS << " debug-instr-number " << Num;
+    OS << LS << "debug-instr-number " << Num;
 
   if (PrintLocations) {
     if (const DebugLoc &DL = MI.getDebugLoc()) {
-      OS << LS << " debug-location ";
+      OS << LS << "debug-location ";
       DL->printAsOperand(OS, State.MST);
     }
   }
diff --git a/llvm/test/CodeGen/MIR/AArch64/return-address-signing.mir b/llvm/test/CodeGen/MIR/AArch64/return-address-signing.mir
index 1030917c87419..302f70fc15192 100644
--- a/llvm/test/CodeGen/MIR/AArch64/return-address-signing.mir
+++ b/llvm/test/CodeGen/MIR/AArch64/return-address-signing.mir
@@ -1,4 +1,4 @@
-# RUN: llc -mtriple=aarch64 -run-pass=prologepilog -run-pass=aarch64-ptrauth -o - %s 2>&1 | FileCheck %s
+# RUN: llc -mtriple=aarch64 -run-pass=prologepilog -run-pass=aarch64-ptrauth -o - %s 2>&1 | FileCheck --strict-whitespace %s
 --- |
   target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
   target triple = "aarch64"
diff --git a/llvm/unittests/ADT/StringExtrasTest.cpp b/llvm/unittests/ADT/StringExtrasTest.cpp
index fbaed38da5943..af88f88949b77 100644
--- a/llvm/unittests/ADT/StringExtrasTest.cpp
+++ b/llvm/unittests/ADT/StringExtrasTest.cpp
@@ -290,6 +290,12 @@ TEST(StringExtrasTest, ListSeparator) {
   EXPECT_EQ(S, "");
   S = LS2;
   EXPECT_EQ(S, " ");
+
+  ListSeparator LS3(",", "{");
+  S = LS3;
+  EXPECT_EQ(S, "{");
+  S = LS3;
+  EXPECT_EQ(S, ",");
 }
 
 TEST(StringExtrasTest, toStringAPInt) {