[MLIR] Improve doc for -mlir-print-local-scope and unhide

[bondhugula]

Summary

This is a pretty important debugging option to stay hidden. Also,
improve its cmd-line description; the current description gives no hint
that this is the one to use to have locations printed inline.
Out-of-line locations are also unproductive to work with in many cases
where the locations are actually compact, which is also why this option
should be more visible. This revision doesn't change the default on it
though.

[bondhugula]

Ideally, if this option shouldn't be hidden, inline location printing should get its own flag that is visible -- just like -mlir-print-debuginfo is visible?

[rriddle]

In D117186#3239610, @bondhugula wrote:

Ideally, if this option shouldn't be hidden, inline location printing should get its own flag that is visible -- just like -mlir-print-debuginfo is visible?

Inline location printing is related to if aliases are enabled or not, though it's likely not immediately obvious that those are just attributes. What would such a flag provide over print-local-scope?

mlir/lib/IR/AsmPrinter.cpp

147

Can you tweak this to mention that attribute/type aliases are disabled? (which is why locations are printed inline).

[bondhugula]

In D117186#3239613, @rriddle wrote:

In D117186#3239610, @bondhugula wrote:

Ideally, if this option shouldn't be hidden, inline location printing should get its own flag that is visible -- just like -mlir-print-debuginfo is visible?

Inline location printing is related to if aliases are enabled or not, though it's likely not immediately obvious that those are just attributes. What would such a flag provide over print-local-scope?

1. You'll be able to keep print-local-scope hidden like before (if that was the right thing) while unhiding the other flag.
2. print-local-scope gives no inkling that it would enable inline location printing (a search of mlir-opt -h or -help-hidden wouldn't help). Although I already knew there was some flag that allowed printing locations inline, it took me 15 min to find that again. I remember digging it from the commit message about 3 months ago but this isn't easy to remember. (A hidden flag makes it worse.) Having "location" in the help message or in the flag will definitely help.

[bondhugula]

mlir/lib/IR/AsmPrinter.cpp

147

This would be too much information for a help message I think. Any suggestions on the phrasing?

[jpienaar]

mlir/lib/IR/AsmPrinter.cpp

147

"Print with all info inline (elides aliases)" ? Info is a bit broad but loc/attr/type may be too long. Alternatively perhaps "Print with all aliases expanded and elides" may not be much better.

I agree that local scope assumes more knowledge of internals than is strictly needed.

[bondhugula]

mlir/lib/IR/AsmPrinter.cpp

147

Thanks, @jpienaar -- I think these make it more understandable. Slightly longer is fine. Does "loc/attr/type" cover it all? There is local SSA numbering I think that's in fact a prominent part. Otherwise, this would be useful to users:

Print with inline information (eliding aliases for attributes, types, and locations)

[bondhugula]

Tweak message.

mlir/lib/IR/AsmPrinter.cpp

struct AsmPrinterOptions {
   // Use the generic op output form in the operation printer even if the custom
   // form is defined.
   llvm::cl::opt<bool> printGenericOpFormOpt{
       "mlir-print-op-generic", llvm::cl::init(false),
       llvm::cl::desc("Print the generic op form"), llvm::cl::Hidden};
 
   llvm::cl::opt<bool> printLocalScopeOpt{
       "mlir-print-local-scope", llvm::cl::init(false),
-      llvm::cl::desc("Print assuming in local scope by default"),
-      llvm::cl::Hidden};
+      llvm::cl::desc("Print with local scope and inline information (eliding "
+                     "aliases for attributes, types, and locations")};
 };
 } // namespace
 
 static llvm::ManagedStatic<AsmPrinterOptions> clOptions;
 
 /// Register a set of useful command-line options that can be used to configure
 /// various flags within the AsmPrinter.
 void mlir::registerAsmPrinterCLOptions() {