Change pass registration generated code to allow users to selectively register passes

[mehdi_amini]

Summary

This slightly tweaks the generated code from:

#ifdef GEN_PASS_REGISTRATION
::mlir::registerPass("flag1", ...
::mlir::registerPass("flag2", ...
#endif // GEN_PASS_REGISTRATION

to:

#ifdef GEN_PASS_REGISTRATION
#define GEN_PASS_REGISTRATION_Pass1
#define GEN_PASS_REGISTRATION_Pass2
#endif // GEN_PASS_REGISTRATION

#ifdef GEN_PASS_REGISTRATION_Pass1
::mlir::registerPass("flag1", ...
#endif
#ifdef GEN_PASS_REGISTRATION_Pass1
::mlir::registerPass("flag2", ...
#endif

That way the generated code can be included by defining the
GEN_PASS_REGISTRATION macro as currenty and register all the passes,
but one can also define only GEN_PASS_REGISTRATION_Pass1 to register a
subset of the passes.

[rriddle]

Thanks, I have a revision that does this but haven't sent it out for review yet.

mlir/tools/mlir-tblgen/PassGen.cpp

 // GEN: Pass registration generation
 //===----------------------------------------------------------------------===//
 
 /// Emit the code for registering each of the given passes with the global
 /// PassRegistry.
 static void emitRegistration(ArrayRef<Pass> passes, raw_ostream &os) {
   os << "#ifdef GEN_PASS_REGISTRATION\n";
   for (const Pass &pass : passes) {
+    os << llvm::formatv("#define GEN_PASS_REGISTRATION_{0}\n",
+                        pass.getDef()->getName());
+  }
+  os << "#endif // GEN_PASS_REGISTRATION\n";
+
+  for (const Pass &pass : passes) {
+    os << llvm::formatv("#ifdef GEN_PASS_REGISTRATION_{0}\n",
+                        pass.getDef()->getName());
     os << llvm::formatv("::mlir::registerPass(\"{0}\", \"{1}\", []() -> "
                         "std::unique_ptr<Pass> {{ return {2}; });\n",
                         pass.getArgument(), pass.getSummary(),
                         pass.getConstructor());
+    os << llvm::formatv("#endif // GEN_PASS_REGISTRATION_{0}\n",
+                        pass.getDef()->getName());
+    os << llvm::formatv("#undef GEN_PASS_REGISTRATION_{0}\n",
+                        pass.getDef()->getName());
+  }
+
+  os << "#ifdef GEN_PASS_REGISTRATION\n";
+  for (const Pass &pass : passes) {
+    os << llvm::formatv("#undef GEN_PASS_REGISTRATION_{0}\n",
+                        pass.getDef()->getName());
   }
-  os << "#undef GEN_PASS_REGISTRATION\n";
   os << "#endif // GEN_PASS_REGISTRATION\n";
+  os << "#undef GEN_PASS_REGISTRATION\n";
 }
 
 //===----------------------------------------------------------------------===//
 // GEN: Registration hooks
 //===----------------------------------------------------------------------===//
 
 static void emitDecls(const llvm::RecordKeeper &recordKeeper, raw_ostream &os) {
   os << "/* Autogenerated by mlir-tblgen; don't manually edit */\n";