[llc] Add -M for InstPrinter options

[MaskRay]

For many targets, llvm-objdump and llvm-mc
(https://reviews.llvm.org/D103004) support -M no-aliases (e.g.
RISCVInstPrinter::applyTargetSpecificCLOption).

This patch implements -M for llc.

While here, rename "DisassemblerOptions" in llvm-mc to the more
appropriate "InstPrinterOptions". For llvm-mc --assemble, there is no
disassembler involved.

[s-barannikov]

The way it is currently implemented it only works when invoking llc directly.
It would be great if the option could be set by the compiler driver, which passes options in memory.
See

llvm-project/clang/tools/driver/cc1as_main.cpp

Line 538 in eb549da

MCOptions.AsmVerbose = true;

for a few examples.

Some targets prefer to not print aliases by default; there should be a way of enabling this behavior.

[s-barannikov]

---

(nit) There is an overload accepting Twine:

Suggested change

	return createStringError(inconvertibleErrorCode(),
	"invalid InstPrinter option '" + Opt + "'");
	return createStringError("invalid InstPrinter option '" + Opt + "'");

[s-barannikov]

---

(nit) Could avoid moving the Error twice:

Suggested change

	if (auto Err = MCStreamerOrErr.takeError()) {
	Context.reportError(SMLoc(), toString(std::move(Err)));
	if (!MCStreamerOrErr) {
	Context.reportError(SMLoc(), toString(MCStreamerOrErr.takeError()));

[MaskRay]

The way it is currently implemented it only works when invoking llc directly. It would be great if the option could be set by the compiler driver, which passes options in memory. See

llvm-project/clang/tools/driver/cc1as_main.cpp

Line 538 in eb549da

MCOptions.AsmVerbose = true;

for a few examples.
Some targets prefer to not print aliases by default; there should be a way of enabling this behavior.

Thanks for the quick response. This patch intends to port applyTargetSpecificCLOption to llc to be on par with llvm-mc and llvm-objdump.

You are right that Clang cc1as sets MCTargetOptions in a different place. If we want to add a clang -cc1 and -cc1as option, the clang file needs to be modified. That isn't my motivation, though. (Skimming through GCC's manpage I don't find a similar option. If we add an option, we have some freedom on the naming.)

[s-barannikov]

I'm not against the current approach, it is just I'm not sure that this option would be as useful for llc without allowing it to be forwarded from the driver. llc is more a developer tool than an end-user tool. I doubt developers will want to pass this option to llc (what for?).