[NFC] [DebugCounter] warn if --debug-counter is unused in NDEBUG

[fmayer]

No description provided.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Florian Mayer (fmayer)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/143057.diff

1 Files Affected:

• (modified) llvm/lib/Support/DebugCounter.cpp (+5)

diff --git a/llvm/lib/Support/DebugCounter.cpp b/llvm/lib/Support/DebugCounter.cpp
index 9c4a4429ca0ee..1fbd700afa1d7 100644
--- a/llvm/lib/Support/DebugCounter.cpp
+++ b/llvm/lib/Support/DebugCounter.cpp
@@ -172,6 +172,11 @@ DebugCounter &DebugCounter::instance() {
 void DebugCounter::push_back(const std::string &Val) {
   if (Val.empty())
     return;
+#ifdef NDEBUG
+  // isCountingEnabled is hardcoded to false in NDEBUG.
+  errs() << "Requested --debug-counter in non-debug LLVM build. This is a "
+            "no-op.\n";
+#endif
 
   // The strings should come in as counter=chunk_list
   auto CounterPair = StringRef(Val).split('=');

[nikic]

LGTM

I was wondering whether we could just unconditionally enable debug counters, but doing that does have some meaningful overhead: https://llvm-compile-time-tracker.com/compare.php?from=100a1d0c4caad0d0f2ec26b07d3cc73f59b9a9a8&to=341c03268229f2982df1fd7ddb5e3db7a2e7731a&stat=instructions:u

[github-actions]

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