[DebugCounter] Add -print-debug-counter-queries option

[nikic]

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.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Nikita Popov (nikic)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/162827.diff

3 Files Affected:

• (modified) llvm/include/llvm/Support/DebugCounter.h (+3)
• (modified) llvm/lib/Support/DebugCounter.cpp (+36-20)
• (modified) llvm/test/Other/debugcounter-dce.ll (+9-1)

diff --git a/llvm/include/llvm/Support/DebugCounter.h b/llvm/include/llvm/Support/DebugCounter.h
index 48fc60035b189..1b30efa740298 100644
--- a/llvm/include/llvm/Support/DebugCounter.h
+++ b/llvm/include/llvm/Support/DebugCounter.h
@@ -178,6 +178,7 @@ class DebugCounter {
     std::string Desc;
     SmallVector<Chunk> Chunks;
   };
+  LLVM_ABI 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;
 };
 
diff --git a/llvm/lib/Support/DebugCounter.cpp b/llvm/lib/Support/DebugCounter.cpp
index 6b65720440f30..5ab1def43313b 100644
--- a/llvm/lib/Support/DebugCounter.cpp
+++ b/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;
   }
diff --git a/llvm/test/Other/debugcounter-dce.ll b/llvm/test/Other/debugcounter-dce.ll
index 54d929f219aef..3b1dfb453593a 100644
--- a/llvm/test/Other/debugcounter-dce.ll
+++ b/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

[dtcxzyw]

in order to find the correct counter value to use to hit a specific point in the transform.

Can't we use utils/bisect-skip-count + grep to find the point?

[nikic]

in order to find the correct counter value to use to hit a specific point in the transform.

Can't we use utils/bisect-skip-count + grep to find the point?

In theory yes, but this is a very complicated and slow way to do it.

To clarify the use case: When looking at an InstCombine log, I want to see how the IR looked like at a specific point in the transform log. This is easy to do if I can get the debug counter at that point. I could of course write a bash script that greps for some part of the log (which may be a bit tricky due to instruction revisits) and bisect using it, but it's quite roundabout.

[dtcxzyw]

LGTM.

[fmayer]

does this need to be ABI? This doesn't seem to be used inline