[Support] Optimize DebugCounter hot path (NFC) (llvm#170260)

When enabling ShouldPrintCounter, also set Enabled, so that we only have
to check one of them. This cuts down the cost of (disabled) debug
counters by half.

Author: nikic

llvm/include/llvm/Support/DebugCounter.h

@@ -158,7 +158,7 @@ class DebugCounter {
 #ifdef NDEBUG
     return false;
 #else
-    return instance().Enabled || instance().ShouldPrintCounter;
+    return instance().Enabled;
 #endif
   }
 

llvm/lib/Support/DebugCounter.cpp

@@ -135,7 +135,11 @@ struct DebugCounterOwner : DebugCounter {
       cl::Optional,
       cl::location(this->ShouldPrintCounter),
       cl::init(false),
-      cl::desc("Print out debug counter info after all counters accumulated")};
+      cl::desc("Print out debug counter info after all counters accumulated"),
+      cl::callback([&](const bool &Value) {
+        if (Value)
+          enableAllCounters();
+      })};
   cl::opt<bool, true> PrintDebugCounterQueries{
       "print-debug-counter-queries",
       cl::Hidden,