Enable the %s modifier in inline asm template string

[nemanjai]

Summary

It appears that there is code in glibc that uses this modifier so LLVM should handle it.
Honestly, I could not locate any documentation specifying the semantics of this modifier so I implemented it to have the same behaviour that I observed from GCC. Perhaps if one of the reviewers has this information, you can offer what needs to be done to the operand when the %s modifier is in the template.

[wschmidt]

Yes, that's the correct behavior, as can be seen at https://gcc.gnu.org/ml/gcc-patches/2016-01/msg01937.html. Note that GCC produces a warning if the wrong operand type is used, but I don't see that as a necessity for something that's deprecated anyway. This patch LGTM.

[nemanjai]

Committed revision 259798.

lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp

case 'c': // Substitute immediate value without immediate syntax
         return true;
       O << MO.getImm();
       return false;
     case 'n':  // Negate the immediate constant.
       if (MO.getType() != MachineOperand::MO_Immediate)
         return true;
       O << -MO.getImm();
       return false;
+    case 's':  // The GCC deprecated s modifier
+      if (MO.getType() != MachineOperand::MO_Immediate)
+        return true;
+      O << ((32 - MO.getImm()) & 31);
+      return false;
     }
   }
   return true;
 }
 
 bool AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
                                        unsigned AsmVariant,
                                        const char *ExtraCode, raw_ostream &O) {
   // Target doesn't support this yet!
   return true;
 }
 
 void AsmPrinter::emitInlineAsmStart() const {}
 
 void AsmPrinter::emitInlineAsmEnd(const MCSubtargetInfo &StartInfo,
                                   const MCSubtargetInfo *EndInfo) const {}