[DebugCounter] Add -print-debug-counter-queries option (#162827)

Add a `-print-debug-counter-queries` option which prints the current
value of the counter and whether it is executed/skipped each time it is
queried. This is useful when interleaving the output with the usual
transform debug output, in order to find the correct counter value to
use to hit a specific point in the transform.

Author: nikic

llvm/include/llvm/Support/DebugCounter.h

@@ -178,6 +178,7 @@ class DebugCounter {
     std::string Desc;
     SmallVector<Chunk> Chunks;
   };
+  bool handleCounterIncrement(CounterInfo &Info);
 
   DenseMap<unsigned, CounterInfo> Counters;
   CounterVector RegisteredCounters;
@@ -188,6 +189,8 @@ class DebugCounter {
 
   bool ShouldPrintCounter = false;
 
+  bool ShouldPrintCounterQueries = false;
+
   bool BreakOnLast = false;
 };
 

llvm/lib/Support/DebugCounter.cpp

@@ -136,6 +136,13 @@ struct DebugCounterOwner : DebugCounter {
       cl::location(this->ShouldPrintCounter),
       cl::init(false),
       cl::desc("Print out debug counter info after all counters accumulated")};
+  cl::opt<bool, true> PrintDebugCounterQueries{
+      "print-debug-counter-queries",
+      cl::Hidden,
+      cl::Optional,
+      cl::location(this->ShouldPrintCounterQueries),
+      cl::init(false),
+      cl::desc("Print out each query of an enabled debug counter")};
   cl::opt<bool, true> BreakOnLastCount{
       "debug-counter-break-on-last",
       cl::Hidden,
@@ -221,31 +228,40 @@ void DebugCounter::print(raw_ostream &OS) const {
   }
 }
 
+bool DebugCounter::handleCounterIncrement(CounterInfo &Info) {
+  int64_t CurrCount = Info.Count++;
+  uint64_t CurrIdx = Info.CurrChunkIdx;
+
+  if (Info.Chunks.empty())
+    return true;
+  if (CurrIdx >= Info.Chunks.size())
+    return false;
+
+  bool Res = Info.Chunks[CurrIdx].contains(CurrCount);
+  if (BreakOnLast && CurrIdx == (Info.Chunks.size() - 1) &&
+      CurrCount == Info.Chunks[CurrIdx].End) {
+    LLVM_BUILTIN_DEBUGTRAP;
+  }
+  if (CurrCount > Info.Chunks[CurrIdx].End) {
+    Info.CurrChunkIdx++;
+
+    /// Handle consecutive blocks.
+    if (Info.CurrChunkIdx < Info.Chunks.size() &&
+        CurrCount == Info.Chunks[Info.CurrChunkIdx].Begin)
+      return true;
+  }
+  return Res;
+}
+
 bool DebugCounter::shouldExecuteImpl(unsigned CounterName) {
   auto &Us = instance();
   auto Result = Us.Counters.find(CounterName);
   if (Result != Us.Counters.end()) {
     auto &CounterInfo = Result->second;
-    int64_t CurrCount = CounterInfo.Count++;
-    uint64_t CurrIdx = CounterInfo.CurrChunkIdx;
-
-    if (CounterInfo.Chunks.empty())
-      return true;
-    if (CurrIdx >= CounterInfo.Chunks.size())
-      return false;
-
-    bool Res = CounterInfo.Chunks[CurrIdx].contains(CurrCount);
-    if (Us.BreakOnLast && CurrIdx == (CounterInfo.Chunks.size() - 1) &&
-        CurrCount == CounterInfo.Chunks[CurrIdx].End) {
-      LLVM_BUILTIN_DEBUGTRAP;
-    }
-    if (CurrCount > CounterInfo.Chunks[CurrIdx].End) {
-      CounterInfo.CurrChunkIdx++;
-
-      /// Handle consecutive blocks.
-      if (CounterInfo.CurrChunkIdx < CounterInfo.Chunks.size() &&
-          CurrCount == CounterInfo.Chunks[CounterInfo.CurrChunkIdx].Begin)
-        return true;
+    bool Res = Us.handleCounterIncrement(CounterInfo);
+    if (Us.ShouldPrintCounterQueries && CounterInfo.IsSet) {
+      dbgs() << "DebugCounter " << Us.RegisteredCounters[CounterName] << "="
+             << (CounterInfo.Count - 1) << (Res ? " execute" : " skip") << "\n";
     }
     return Res;
   }

llvm/test/Other/debugcounter-dce.ll

@@ -1,8 +1,16 @@
 ; REQUIRES: asserts
-; RUN: opt -passes=dce -S -debug-counter=dce-transform=1-2  < %s | FileCheck %s
+; RUN: opt -passes=dce -S -debug-counter=dce-transform=1-2  < %s | FileCheck %s --check-prefixes=CHECK,NO-PRINT
+; RUN: opt -passes=dce -S -debug-counter=dce-transform=1-2 -print-debug-counter-queries < %s 2>&1 | FileCheck %s --check-prefixes=CHECK,PRINT
 ;; Test that, with debug counters on, we will skip the first DCE opportunity, perform next 2,
 ;; and ignore all the others left.
 
+; NO-PRINT-NOT: DebugCounter
+; PRINT: DebugCounter dce-transform=0 skip
+; PRINT-NEXT: DebugCounter dce-transform=1 execute
+; PRINT-NEXT: DebugCounter dce-transform=2 execute
+; PRINT-NEXT: DebugCounter dce-transform=3 skip
+; PRINT-NEXT: DebugCounter dce-transform=4 skip
+
 ; CHECK-LABEL: @test
 ; CHECK-NEXT: %add1 = add i32 1, 2
 ; CHECK-NEXT: %sub1 = sub i32 %add1, 1