[X86] Use StringRef::consume_back (NFC) (#139417)

This patch uses consume_back while changing the type of TrailingDot to
bool, indicating whether we have consumed "." or not.

Author: kazutakahirata

llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp

@@ -2378,7 +2378,7 @@ bool X86AsmParser::ParseIntelDotOperator(IntelExprStateMachine &SM,
   // Drop the optional '.'.
   StringRef DotDispStr = Tok.getString();
   DotDispStr.consume_front(".");
-  StringRef TrailingDot;
+  bool TrailingDot = false;
 
   // .Imm gets lexed as a real.
   if (Tok.is(AsmToken::Real)) {
@@ -2388,10 +2388,7 @@ bool X86AsmParser::ParseIntelDotOperator(IntelExprStateMachine &SM,
     Info.Offset = DotDisp.getZExtValue();
   } else if ((isParsingMSInlineAsm() || getParser().isParsingMasm()) &&
              Tok.is(AsmToken::Identifier)) {
-    if (DotDispStr.ends_with(".")) {
-      TrailingDot = DotDispStr.substr(DotDispStr.size() - 1);
-      DotDispStr = DotDispStr.drop_back(1);
-    }
+    TrailingDot = DotDispStr.consume_back(".");
     const std::pair<StringRef, StringRef> BaseMember = DotDispStr.split('.');
     const StringRef Base = BaseMember.first, Member = BaseMember.second;
     if (getParser().lookUpField(SM.getType(), DotDispStr, Info) &&
@@ -2409,8 +2406,8 @@ bool X86AsmParser::ParseIntelDotOperator(IntelExprStateMachine &SM,
   const char *DotExprEndLoc = DotDispStr.data() + DotDispStr.size();
   while (Tok.getLoc().getPointer() < DotExprEndLoc)
     Lex();
-  if (!TrailingDot.empty())
-    getLexer().UnLex(AsmToken(AsmToken::Dot, TrailingDot));
+  if (TrailingDot)
+    getLexer().UnLex(AsmToken(AsmToken::Dot, "."));
   SM.addImm(Info.Offset);
   SM.setTypeInfo(Info.Type);
   return false;