[llvm] [mlir] [MLIR] Update GreedyRewriter to use the LDBG() debug log mechanism (NFC) (PR #153961)

[Mehdi Amini via llvm-commits]

https://github.com/joker-eph updated https://github.com/llvm/llvm-project/pull/153961

>From c49665a6c4daa34e0e22eace6cb005e3f59c6726 Mon Sep 17 00:00:00 2001
From: Mehdi Amini <joker.eph at gmail.com>
Date: Sat, 16 Aug 2025 08:22:28 -0700
Subject: [PATCH] [MLIR] Update GreedyRewriter to use the LDBG() debug log
 mechanism (NFC)

Also improve a bit the doc in the LDBG() implementation
---
 llvm/include/llvm/Support/DebugLog.h          | 20 ++++++-------
 .../Transforms/Utils/DialectConversion.cpp    |  4 +--
 .../Utils/GreedyPatternRewriteDriver.cpp      | 30 +++++++++++--------
 3 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/llvm/include/llvm/Support/DebugLog.h b/llvm/include/llvm/Support/DebugLog.h
index a94e578c0aa1e..c671ff18aafb7 100644
--- a/llvm/include/llvm/Support/DebugLog.h
+++ b/llvm/include/llvm/Support/DebugLog.h
@@ -89,22 +89,22 @@ namespace impl {
 class LLVM_ABI raw_ldbg_ostream final : public raw_ostream {
   std::string Prefix;
   raw_ostream &Os;
-  bool HasPendingNewline;
+  bool ShouldPrefixNextString;
 
   /// Split the line on newlines and insert the prefix before each
   /// newline. Forward everything to the underlying stream.
   void write_impl(const char *Ptr, size_t Size) final {
     auto Str = StringRef(Ptr, Size);
-    // Handle the initial prefix.
-    if (!Str.empty())
-      writeWithPrefix(StringRef());
-
     auto Eol = Str.find('\n');
+    // Handle `\n` occurring in the string, ensure to print the prefix at the
+    // beginning of each line.
     while (Eol != StringRef::npos) {
+      // Take the line up to the newline (including the newline).
       StringRef Line = Str.take_front(Eol + 1);
       if (!Line.empty())
         writeWithPrefix(Line);
-      HasPendingNewline = true;
+      // We printed a newline, record here to print a prefix.
+      ShouldPrefixNextString = true;
       Str = Str.drop_front(Eol + 1);
       Eol = Str.find('\n');
     }
@@ -119,16 +119,16 @@ class LLVM_ABI raw_ldbg_ostream final : public raw_ostream {
 
 public:
   explicit raw_ldbg_ostream(std::string Prefix, raw_ostream &Os,
-                            bool HasPendingNewline = true)
+                            bool ShouldPrefixNextString = true)
       : Prefix(std::move(Prefix)), Os(Os),
-        HasPendingNewline(HasPendingNewline) {
+        ShouldPrefixNextString(ShouldPrefixNextString) {
     SetUnbuffered();
   }
   ~raw_ldbg_ostream() final { flushEol(); }
   void flushEol() {
-    if (HasPendingNewline) {
+    if (ShouldPrefixNextString) {
       emitPrefix();
-      HasPendingNewline = false;
+      ShouldPrefixNextString = false;
     }
   }
 
diff --git a/mlir/lib/Transforms/Utils/DialectConversion.cpp b/mlir/lib/Transforms/Utils/DialectConversion.cpp
index ff34a58965763..2877090354588 100644
--- a/mlir/lib/Transforms/Utils/DialectConversion.cpp
+++ b/mlir/lib/Transforms/Utils/DialectConversion.cpp
@@ -1138,8 +1138,8 @@ struct ConversionPatternRewriterImpl : public RewriterBase::Listener {
   SmallPtrSet<Operation *, 1> pendingRootUpdates;
 
   /// A raw output stream used to prefix the debug log.
-  llvm::impl::raw_ldbg_ostream os{(Twine("[") + DEBUG_TYPE + "] ").str(),
-                                  llvm::dbgs(), /*HasPendingNewline=*/false};
+  llvm::impl::raw_ldbg_ostream os{(Twine("[") + DEBUG_TYPE + ":1] ").str(),
+                                  llvm::dbgs()};
 
   /// A logger used to emit diagnostics during the conversion process.
   llvm::ScopedPrinter logger{os};
diff --git a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
index 607b86cb86315..e7b49b4b494dc 100644
--- a/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
+++ b/mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
@@ -15,6 +15,8 @@
 #include "mlir/Config/mlir-config.h"
 #include "mlir/IR/Action.h"
 #include "mlir/IR/Matchers.h"
+#include "mlir/IR/Operation.h"
+#include "mlir/IR/OperationSupport.h"
 #include "mlir/IR/Verifier.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 #include "mlir/Rewrite/PatternApplicator.h"
@@ -23,7 +25,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/ScopeExit.h"
-#include "llvm/Support/Debug.h"
+#include "llvm/Support/DebugLog.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -178,9 +180,8 @@ static Operation *getDumpRootOp(Operation *op) {
   return op;
 }
 static void logSuccessfulFolding(Operation *op) {
-  llvm::dbgs() << "// *** IR Dump After Successful Folding ***\n";
-  op->dump();
-  llvm::dbgs() << "\n\n";
+  LDBG() << "// *** IR Dump After Successful Folding ***\n"
+         << OpWithFlags(op, OpPrintingFlags().elideLargeElementsAttrs());
 }
 #endif // NDEBUG
 
@@ -394,8 +395,13 @@ class GreedyPatternRewriteDriver : public RewriterBase::Listener {
                      function_ref<void(Diagnostic &)> reasonCallback) override;
 
 #ifndef NDEBUG
+  /// A raw output stream used to prefix the debug log.
+
+  llvm::impl::RAIINewLineStream dbgsWithNewLine{llvm::dbgs()};
+  llvm::impl::raw_ldbg_ostream os{(Twine("[") + DEBUG_TYPE + ":1] ").str(),
+                                  dbgsWithNewLine};
   /// A logger used to emit information during the application process.
-  llvm::ScopedPrinter logger{llvm::dbgs()};
+  llvm::ScopedPrinter logger{os};
 #endif
 
   /// The low-level pattern applicator.
@@ -917,10 +923,9 @@ mlir::applyPatternsGreedily(Region &region,
   RegionPatternRewriteDriver driver(region.getContext(), patterns, config,
                                     region);
   LogicalResult converged = std::move(driver).simplify(changed);
-  LLVM_DEBUG(if (failed(converged)) {
-    llvm::dbgs() << "The pattern rewrite did not converge after scanning "
-                 << config.getMaxIterations() << " times\n";
-  });
+  if (failed(converged))
+    LDBG() << "The pattern rewrite did not converge after scanning "
+           << config.getMaxIterations() << " times\n";
   return converged;
 }
 
@@ -1052,9 +1057,8 @@ LogicalResult mlir::applyOpPatternsGreedily(
   LogicalResult converged = std::move(driver).simplify(ops, changed);
   if (allErased)
     *allErased = surviving.empty();
-  LLVM_DEBUG(if (failed(converged)) {
-    llvm::dbgs() << "The pattern rewrite did not converge after "
-                 << config.getMaxNumRewrites() << " rewrites";
-  });
+  if (failed(converged))
+    LDBG() << "The pattern rewrite did not converge after "
+           << config.getMaxNumRewrites() << " rewrites";
   return converged;
 }