[llvm] Mark STATISTIC variables as maybe_unused when stats are disabled. (PR #159103)

[James Y Knight via llvm-commits]

https://github.com/jyknight created https://github.com/llvm/llvm-project/pull/159103

PR #159045 made the constructor constexpr, which allows `-Wunused-variable` to trigger. However, we don't really care if a statistic is unused if `LLVM_ENABLE_STATS` is 0.

>From 2869bcd42e8045939598b91c62152a356be933ee Mon Sep 17 00:00:00 2001
From: James Y Knight <jyknight at google.com>
Date: Tue, 16 Sep 2025 10:02:18 -0400
Subject: [PATCH] Mark STATISTIC variables as maybe_unused when stats are
 disabled.

PR #159045 made the constructor constexpr, which allows `-Wunused-variable` to trigger. However, we don't really care if a statistic is unused if `LLVM_ENABLE_STATS` is 0.
---
 llvm/include/llvm/ADT/Statistic.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/include/llvm/ADT/Statistic.h b/llvm/include/llvm/ADT/Statistic.h
index 795b0c2082c77..75d608beb0134 100644
--- a/llvm/include/llvm/ADT/Statistic.h
+++ b/llvm/include/llvm/ADT/Statistic.h
@@ -164,8 +164,13 @@ using Statistic = NoopStatistic;
 
 // STATISTIC - A macro to make definition of statistics really simple.  This
 // automatically passes the DEBUG_TYPE of the file into the statistic.
+#if LLVM_ENABLE_STATS
 #define STATISTIC(VARNAME, DESC)                                               \
   static llvm::Statistic VARNAME = {DEBUG_TYPE, #VARNAME, DESC}
+#else
+#define STATISTIC(VARNAME, DESC)                                               \
+  static llvm::Statistic VARNAME [[maybe_unused]] = {DEBUG_TYPE, #VARNAME, DESC}
+#endif
 
 // ALWAYS_ENABLED_STATISTIC - A macro to define a statistic like STATISTIC but
 // it is enabled even if LLVM_ENABLE_STATS is off.