default tied output register

[MikeStump]

Summary

This implements default tied output registers.

[MikeStump]

Ping?

[MikeStump]

Ping?

[arsenm]

It's not obvious to me what this accomplishes, and needs tests

[MikeStump]

What this accomplishes is listed in the summary and isn't meant to be opaque. https://reviews.llvm.org/D35998 in theory has a way to see it work, you can ask them for an in tree test case.

I have a port that requires default tied output registers to work. Requiring the submission of a port to bug fix an existing feature isn't the right path forward.

I have rather trivial little instructions that use default tied output registers, and they're completely broken without the patch. Trivially, the original author didn't think about the easy cases, as my instructions are rather trivial. I'd like to think my patch handles even the hard cases, but, I didn't prove to myself that it is complete. I believe it is monotonically closer however.

[arsenm]

In D32461#1871151, @MikeStump wrote:

What this accomplishes is listed in the summary and isn't meant to be opaque. https://reviews.llvm.org/D35998 in theory has a way to see it work, you can ask them for an in tree test case.

Commit message needs more elaboration. Default tied output registers already look implemented to me, and this is an asm matcher problem. The case handled here also looks implemented, so this needs an explanation for what this is fixing

utils/TableGen/AsmMatcherEmitter.cpp

   CvtOS << "  const uint8_t *Converter = ConversionTable[Kind];\n";
   if (HasOptionalOperands) {
     CvtOS << "  unsigned NumDefaults = 0;\n";
   }
   CvtOS << "  unsigned OpIdx;\n";
   CvtOS << "  Inst.setOpcode(Opcode);\n";
   CvtOS << "  for (const uint8_t *p = Converter; *p; p+= 2) {\n";
   if (HasOptionalOperands) {
-    CvtOS << "    OpIdx = *(p + 1) - NumDefaults;\n";
+    CvtOS << "    OpIdx = *(p + 1) - countPopulation(NumDefaults<<(sizeof(unsigned)*8-1-p[1]));\n";
   } else {
     CvtOS << "    OpIdx = *(p + 1);\n";
   }
   CvtOS << "    switch (*p) {\n";
   CvtOS << "    default: llvm_unreachable(\"invalid conversion entry!\");\n";
   CvtOS << "    case CVT_Reg:\n";
   CvtOS << "      static_cast<" << TargetOperandClass
         << "&>(*Operands[OpIdx]).addRegOperands(Inst, 1);\n";

         if (Op.Class->IsOptional) {
           // If optional operand is not present in actual instruction then we
           // should call its DefaultMethod before RenderMethod
           assert(HasOptionalOperands);
           CvtOS << "      if (OptionalOperandsMask[*(p + 1) - 1]) {\n"
                 << "        " << Op.Class->DefaultMethod << "()"
                 << "->" << Op.Class->RenderMethod << "(Inst, "
                 << OpInfo.MINumOperands << ");\n"
-                << "        ++NumDefaults;\n"
+                << "        NumDefaults |= 1<<(p[1]+1);\n"
                 << "      } else {\n"
                 << "        static_cast<" << TargetOperandClass
                 << "&>(*Operands[OpIdx])." << Op.Class->RenderMethod
                 << "(Inst, " << OpInfo.MINumOperands << ");\n"
                 << "      }\n";
         } else {
           CvtOS << "      static_cast<" << TargetOperandClass
                 << "&>(*Operands[OpIdx])." << Op.Class->RenderMethod