[Tablegen] Fix AsmString parser misreading optional operands.

[mwahab]

An instruction alias defined with InstAlias and an optional operand in the
middle of the AsmString field, "..${a} <operands>", would get the final
"}" printed in the instruction disassembly. This wouldn't happen if the optional
operand appeared as the last item in the AsmString which is how the current
backends avoided the problem.

There don't appear to be any tests for this part of Tablegen but it passes the
pre-commit tests. Manually tested the change by enabling the generic alias
printer in the ARM backend and checking the output.

[mwahab]

Ping

Tim, you wrote the original code, can you take a look?

Thanks,
Matthew

[t.p.northover]

The changes look reasonable, but it'd be good to have some context on why you're doing it. Is this a prelude to enabling the Alias printing on ARM instead of using the custom code?

Cheers.

Tim.

[mwahab]

From: Tim Northover [mailto:[e-mail]]
Sent: 16 December 2014 16:18

The changes look reasonable, but it'd be good to have some context on why
you're doing it. Is this a prelude to enabling the Alias printing on ARM
instead of using the custom code?

Thanks for reviewing the patch.

It removes an obstacle to the ARM backend switching, which would probably be a
good thing but is rather more than I'm planning to do. The generic and custom
printers produce different outputs for some instructions and fixing that will
take some care. For now, this is just to fix a bug in the Tablegen output.

There's a second related patch for the Tablegen'd alias printer at
http://reviews.llvm.org/D6530, if you could take a look. I'm not sure whether
you worked on that part though.

Matthew

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http://reviews.llvm.org/D6529

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utils/TableGen/AsmWriterEmitter.cpp

   std::pair<StringRef, StringRef::iterator> parseName(StringRef::iterator Start,
                                                       StringRef::iterator End) {
     StringRef::iterator I = Start;
+    StringRef::iterator Next;
     if (*I == '{') {
       // ${some_name}
       Start = ++I;
       while (I != End && *I != '}')
         ++I;
+      Next = I;
+      // eat the final '}'
+      if (Next != End)
+        ++Next;
     } else {
       // $name, just eat the usual suspects.
       while (I != End &&
              ((*I >= 'a' && *I <= 'z') || (*I >= 'A' && *I <= 'Z') ||
               (*I >= '0' && *I <= '9') || *I == '_'))
         ++I;
+      Next = I;
     }
 
-    return std::make_pair(StringRef(Start, I - Start), I);
+    return std::make_pair(StringRef(Start, I - Start), Next);
   }
 
   void print(raw_ostream &O) {