JIT: Don't clone or unroll cold loops (#115744)

Companion to #115734.

Author: amanasifkhalid

src/coreclr/jit/loopcloning.cpp

@@ -1885,6 +1885,12 @@ bool Compiler::optShouldCloneLoop(FlowGraphNaturalLoop* loop, LoopCloneContext*
 //
 bool Compiler::optIsLoopClonable(FlowGraphNaturalLoop* loop, LoopCloneContext* context)
 {
+    if (loop->GetHeader()->isRunRarely())
+    {
+        JITDUMP("Loop cloning: rejecting loop " FMT_LP ". Loop is cold.\n", loop->GetIndex());
+        return false;
+    }
+
     const bool           requireIterable = !doesMethodHaveGuardedDevirtualization();
     NaturalLoopIterInfo* iterInfo        = context->GetLoopIterInfo(loop->GetIndex());
 

src/coreclr/jit/optimizer.cpp

@@ -1390,6 +1390,12 @@ bool Compiler::optTryUnrollLoop(FlowGraphNaturalLoop* loop, bool* changedIR)
     assert(UNROLL_LIMIT_SZ[SMALL_CODE] == 0);
     assert(UNROLL_LIMIT_SZ[COUNT_OPT_CODE] == 0);
 
+    if (loop->GetHeader()->isRunRarely())
+    {
+        JITDUMP("Failed to unroll loop " FMT_LP ": Loop is cold.\n", loop->GetIndex());
+        return false;
+    }
+
     NaturalLoopIterInfo iterInfo;
     if (!loop->AnalyzeIteration(&iterInfo))
     {