[asm] Make EmitMSInlineAsmStr and EmitGCCInlineAsmStr more alike

[thakis]

Summary

https://reviews.llvm.org/D71677 copied a bunch of code from
EmitGCCInlineAsmStr() to EmitMSInlineAsmStr() but made a few small
(likely unintentional) changes. This makes these pieces look the same.

No behavior change.

(Why are these functions two copies? No great reason as far as I can tell.
https://reviews.llvm.org/rG1778831a3d1d24ab6545635f63da4d9c5f8f0ac7 did the
split; we might want to undo them at some point. But PR23933 suggests
that a bigger change is planned for this file in the future, so keeping
this incremental for now.)

[hans]

lgtm

llvm/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

case '$': {
       if (*LastEmitted == '{') {     // ${variable}
         ++LastEmitted;               // Consume '{' character.
         HasCurlyBraces = true;
       }
 
       // If we have ${:foo}, then this is not a real operand reference, it is a
       // "magic" string reference, just like in .td files.  Arrange to call
       // PrintSpecial.
-      if (HasCurlyBraces && LastEmitted[0] == ':') {
+      if (HasCurlyBraces && *LastEmitted == ':') {
         ++LastEmitted;
         const char *StrStart = LastEmitted;
         const char *StrEnd = strchr(StrStart, '}');
         if (!StrEnd)
           report_fatal_error("Unterminated ${:foo} operand in inline asm"
                              " string: '" + Twine(AsmStr) + "'");
 
         std::string Val(StrStart, StrEnd);
case '$': {
         ++IDEnd;
 
       unsigned Val;
       if (StringRef(IDStart, IDEnd-IDStart).getAsInteger(10, Val))
         report_fatal_error("Bad $ operand number in inline asm string: '" +
                            Twine(AsmStr) + "'");
       LastEmitted = IDEnd;
 
+      if (Val >= NumOperands-1)
+        report_fatal_error("Invalid $ operand number in inline asm string: '" +
+                           Twine(AsmStr) + "'");
+
       char Modifier[2] = { 0, 0 };
 
       if (HasCurlyBraces) {
         // If we have curly braces, check for a modifier character.  This
         // supports syntax like ${0:u}, which correspond to "%u0" in GCC asm.
         if (*LastEmitted == ':') {
           ++LastEmitted;    // Consume ':' character.
           if (*LastEmitted == 0)
             report_fatal_error("Bad ${:} expression in inline asm string: '" +
                                Twine(AsmStr) + "'");
 
           Modifier[0] = *LastEmitted;
           ++LastEmitted;    // Consume modifier character.
         }
 
         if (*LastEmitted != '}')
           report_fatal_error("Bad ${} expression in inline asm string: '" +
                              Twine(AsmStr) + "'");
         ++LastEmitted;    // Consume '}' character.
       }
 
-      if (Val >= NumOperands-1)
-        report_fatal_error("Invalid $ operand number in inline asm string: '" +
-                           Twine(AsmStr) + "'");
-
       // Okay, we finally have a value number.  Ask the target to print this
       // operand!
       if (CurVariant == -1 || CurVariant == AsmPrinterVariant) {
         unsigned OpNo = InlineAsm::MIOp_FirstOperand;
 
         bool Error = false;
 
         // Scan to find the machine operand number for the operand.