Enabling multiple letters and digits in constraints

[Tilir]

Summary

There was a FIXME in multiletter constraints, that required to make them really any number of letters and digits, and also problems in documentation. This patch is about to fix both.

[echristo]

This is unacceptable for 3.7. Please go ahead and resubmit against ToT if you'd like it there.

What compatibility are we trying to accomplish here with this?

-eric

[Tilir]

Attached new svn diff against top of trunk (r263219)

[Tilir]

In D18036#372495, @echristo wrote:

This is unacceptable for 3.7. Please go ahead and resubmit against ToT if you'd like it there.

What compatibility are we trying to accomplish here with this?

-eric

Resubmitted against ToT

GCC inline assembler constraints compatibility. I found it on private backend, where GCC constraints like "A32" were widely used in inline assembler, and it seems now there are no way to use them. So I asked in mailing list and then made this patch.

[echristo]

This could probably use some tests. If no current upstream port uses the feature though it makes it hard to accept. :(

docs/LangRef.rst

 """"""""""""""""
 After a potential prefix comes constraint code, or codes.
 
-A Constraint Code is either a single letter (e.g. "``r``"), a "``^``" character
-followed by two letters (e.g. "``^wc``"), or "``{``" register-name "``}``"
-(e.g. "``{eax}``").
+A Constraint Code is either a single letter (e.g. "``r``"), a single letter,
+followed by arbitrary digits (e.g. "``A32``", a "``^``" character
+followed by any number of letters and digits (e.g. "``^wc4``"), 
+or "``{``" register-name "``}``" (e.g. "``{eax}``").
 
 The one and two letter constraint codes are typically chosen to be the same as
 GCC's constraint codes.

lib/IR/InlineAsm.cpp

       pCodes = &multipleAlternatives[multipleAlternativeIndex].Codes;
       ++I;
     } else if (*I == '^') {
-      // Multi-letter constraint
-      // FIXME: For now assuming these are 2-character constraints.
-      pCodes->push_back(std::string(I+1, I+3));
-      I += 3;
+      // Multi-letter constraint: any number of letters and digits
+      ++I;
+      std::string code(I, I+1);
+      ++I;
+      while (isalnum(static_cast<unsigned char>(*I))) {
+        code += *I;
+        ++I;
+      }
+      pCodes->push_back(code);
     } else {
-      // Single letter constraint.
-      pCodes->push_back(std::string(I, I+1));
+      // Single letter constraint, or single letter with trailing digits
+      std::string code(I, I+1);
       ++I;
+      while (isdigit(static_cast<unsigned char>(*I))) {
+        code += *I;
+        ++I;
+      }
+      pCodes->push_back(code);
     }
   }