[FIRRTL] Add debug prints to AssignOutputDirs, NFC

Add some basic debugging information to the AssignOutputDirs pass.  This
indicates that the pass is running and what modules are having their
output directories updated.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

lib/Dialect/FIRRTL/Transforms/AssignOutputDirs.cpp

@@ -12,6 +12,7 @@
 #include "circt/Dialect/FIRRTL/FIRRTLOps.h"
 #include "circt/Dialect/FIRRTL/Passes.h"
 #include "circt/Dialect/HW/HWAttributes.h"
+#include "circt/Support/Debug.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/SmallPtrSet.h"
@@ -98,6 +99,7 @@ struct AssignOutputDirsPass
 } // namespace
 
 void AssignOutputDirsPass::runOnOperation() {
+  LLVM_DEBUG(debugPassHeader(this) << "\n");
   SmallString<64> outputDir(outputDirOption);
   if (fs::make_absolute(outputDir)) {
     emitError(mlir::UnknownLoc::get(&getContext()),
@@ -112,6 +114,7 @@ void AssignOutputDirsPass::runOnOperation() {
 
   bool changed = false;
 
+  LLVM_DEBUG(llvm::dbgs() << "Updating modules:\n");
   DenseSet<InstanceGraphNode *> visited;
   for (auto *root : getAnalysis<InstanceGraph>()) {
     for (auto *node : llvm::inverse_post_order_ext(root, visited)) {
@@ -149,12 +152,17 @@ void AssignOutputDirsPass::runOnOperation() {
             hw::OutputFileAttr::getAsDirectory(&getContext(), moduleOutputDir);
         module->setAttr("output_file", f);
         changed = true;
+        LLVM_DEBUG({
+          llvm::dbgs() << "  - name: " << module.getName() << "\n"
+                       << "    directory: " << f.getFilename() << "\n";
+        });
       }
     }
   }
 
   if (!changed)
     markAllAnalysesPreserved();
+  LLVM_DEBUG(debugFooter() << "\n");
 }
 
 std::unique_ptr<mlir::Pass>