Index: llvm/include/llvm/MC/MCAsmInfo.h
===================================================================
--- llvm/include/llvm/MC/MCAsmInfo.h
+++ llvm/include/llvm/MC/MCAsmInfo.h
@@ -126,6 +126,10 @@
   /// "#"
   StringRef CommentString;
 
+  /// This indicates whether the comment character is only accepted as a comment
+  /// at the beginning of statements. Defaults to false.
+  bool RestrictCommentString = false;
+
   /// This is appended to emitted labels.  Defaults to ":"
   const char *LabelSuffix;
 
@@ -549,6 +553,7 @@
   unsigned getCommentColumn() const { return 40; }
 
   StringRef getCommentString() const { return CommentString; }
+  bool getRestrictCommentString() const { return RestrictCommentString; }
   const char *getLabelSuffix() const { return LabelSuffix; }
 
   bool useAssignmentForEHBegin() const { return UseAssignmentForEHBegin; }
Index: llvm/lib/MC/MCParser/AsmLexer.cpp
===================================================================
--- llvm/lib/MC/MCParser/AsmLexer.cpp
+++ llvm/lib/MC/MCParser/AsmLexer.cpp
@@ -660,9 +660,11 @@
 
 bool AsmLexer::isAtStartOfComment(const char *Ptr) {
   StringRef CommentString = MAI.getCommentString();
+  bool RestrictCommentString = MAI.getRestrictCommentString();
 
   if (CommentString.size() == 1)
-    return CommentString[0] == Ptr[0];
+    return CommentString[0] == Ptr[0] &&
+           (!RestrictCommentString || IsAtStartOfStatement);
 
   // Allow # preprocessor commments also be counted as comments for "##" cases
   if (CommentString[1] == '#')
Index: llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmInfo.cpp
===================================================================
--- llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmInfo.cpp
+++ llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmInfo.cpp
@@ -23,7 +23,8 @@
 
   MaxInstLength = 6;
 
-  CommentString = "#";
+  CommentString = AssemblerDialect == AD_HLASM ? "*" : "#";
+  RestrictCommentString = (AssemblerDialect == AD_HLASM);
   ZeroDirective = "\t.space\t";
   Data64bitsDirective = "\t.quad\t";
   UsesELFSectionDirectiveForBSS = true;