[NFC][flang] Added debug option to bisect TBAA tag attachments.

[jeanPerier]

LGTM

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Optimizer/CodeGen/TBAABuilder.h

private:
   // of a box/descriptor.
   mlir::SymbolRefAttr boxMemberTypeDesc;
   // Identity string for "descriptor member" type descriptor.
   static constexpr llvm::StringRef boxMemberTypeDescId = "descriptor member";
 
   // Counter for unique naming of TBAA operations' symbols.
   unsigned tbaaNodeCounter = 0;
 
+  // Number of attached TBAA tags (used for debugging).
+  unsigned tagAttachmentCounter = 0;
+
   // Mapping from a FIR type to the symbol defined by the corresponding
   // TBAATypeDescriptorOp. It must be populated during the type conversion.
   // Currently unused.
   llvm::DenseMap<mlir::Type, mlir::SymbolRefAttr> typeDescMap;
 
   // Each TBAA tag is a tuple of <baseTypeSym, accessTypeSym, offset>.
   // This map holds TBAATagOp symbol for each unique tuple.
   llvm::DenseMap<std::tuple<mlir::SymbolRefAttr, mlir::SymbolRefAttr, int64_t>,
                  mlir::SymbolRefAttr>
       tagsMap;
 };
 
 } // namespace fir
 
 #endif // FORTRAN_OPTIMIZER_CODEGEN_TBAABUILDER_H

flang/lib/Optimizer/CodeGen/TBAABuilder.cpp

 //===-- TBAABuilder.cpp -- TBAA builder definitions -----------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
 //
 //===----------------------------------------------------------------------===//
 
 #include "TBAABuilder.h"
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "flang-tbaa-builder"
 
 using namespace mlir;
 using namespace mlir::LLVM;
 
 static llvm::cl::opt<bool> disableTBAA(
     "disable-tbaa",
     llvm::cl::desc("disable attaching TBAA tags to memory accessing operations "
                    "to override default Flang behavior"),
     llvm::cl::init(false));
 
+// tagAttachmentLimit is a debugging option that allows limiting
+// the number of TBAA access tag attributes attached to operations.
+// It is set to kTagAttachmentUnlimited by default denoting "no limit".
+static constexpr unsigned kTagAttachmentUnlimited =
+    std::numeric_limits<unsigned>::max();
+static llvm::cl::opt<unsigned>
+    tagAttachmentLimit("tbaa-attach-tag-max", llvm::cl::desc(""),
+                       llvm::cl::init(kTagAttachmentUnlimited));
+
 namespace fir {
 std::string TBAABuilder::getNewTBAANodeName(llvm::StringRef basename) {
   return (llvm::Twine(basename) + llvm::Twine('_') +
           llvm::Twine(tbaaNodeCounter++))
       .str();
 }
 
 TBAABuilder::TBAABuilder(mlir::ModuleOp module, bool applyTBAA)
TBAABuilder::TBAABuilder(mlir::ModuleOp module, bool applyTBAA)
   // is a no-op).
   if (llvm::any_of(
           module.getBodyRegion().getOps<LLVM::MetadataOp>(),
           [&](auto metaOp) { return metaOp.getSymName() == tbaaMetaOpName; })) {
     enableTBAA = false;
     return;
   }
 
+  LLVM_DEBUG(llvm::dbgs() << "Creating TBAA MetadataOp for module '"
+                          << module.getName().value_or("<unknown>") << "'\n");
+
   // Create TBAA MetadataOp with the root and basic type descriptors.
   Location loc = module.getLoc();
   MLIRContext *context = module.getContext();
   OpBuilder builder(module.getBody(), module.getBody()->end());
   tbaaMetaOp = builder.create<MetadataOp>(loc, tbaaMetaOpName);
   builder.setInsertionPointToStart(&tbaaMetaOp.getBody().front());
 
   // Root node.
SymbolRefAttr TBAABuilder::getDataAccessTag(Type baseFIRType,
   return getAnyDataAccessTag();
 }
 
 void TBAABuilder::attachTBAATag(Operation *op, Type baseFIRType,
                                 Type accessFIRType, GEPOp gep) {
   if (!enableTBAA)
     return;
 
+  ++tagAttachmentCounter;
+  if (tagAttachmentLimit != kTagAttachmentUnlimited &&
+      tagAttachmentCounter > tagAttachmentLimit)
+    return;
+
+  LLVM_DEBUG(llvm::dbgs() << "Attaching TBAA tag #" << tagAttachmentCounter
+                          << "\n");
+
   SymbolRefAttr tbaaTagSym;
   if (baseFIRType.isa<fir::BaseBoxType>())
     tbaaTagSym = getBoxAccessTag(baseFIRType, accessFIRType, gep);
   else
     tbaaTagSym = getDataAccessTag(baseFIRType, accessFIRType, gep);
 
   if (tbaaTagSym)
     op->setAttr(LLVMDialect::getTBAAAttrName(),
                 ArrayAttr::get(op->getContext(), tbaaTagSym));
 }
 
 } // namespace fir