Merge branch 'main' into users/meinersbur/flang_runtime_split-headersusers/meinersbur/flang_runtime_split-headers

1 files changed, 18 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MLRegAllocEvictAdvisor.cpp b/llvm/lib/CodeGen/MLRegAllocEvictAdvisor.cpp
index 03f015f8c9e3..9c6487b40d60 100644
--- a/llvm/lib/CodeGen/MLRegAllocEvictAdvisor.cpp
+++ b/llvm/lib/CodeGen/MLRegAllocEvictAdvisor.cpp
@@ -63,6 +63,12 @@ static cl::opt<std::string> InteractiveChannelBaseName(
         "outgoing name should be "
         "<regalloc-evict-interactive-channel-base>.out"));
 
+static cl::opt<unsigned>
+    MaxCascade("mlregalloc-max-cascade", cl::Hidden,
+               cl::desc("The maximum number of times a live range can be "
+                        "evicted before preventing it from being evicted"),
+               cl::init(20));
+
 // Options that only make sense in development mode
 #ifdef LLVM_HAVE_TFLITE
 #include "RegAllocScore.h"
@@ -554,7 +560,7 @@ private:
   std::unique_ptr<Logger> Log;
 };
 
-#endif //#ifdef LLVM_HAVE_TFLITE
+#endif // #ifdef LLVM_HAVE_TFLITE
 } // namespace
 
 float MLEvictAdvisor::getInitialQueueSize(const MachineFunction &MF) {
@@ -643,8 +649,18 @@ bool MLEvictAdvisor::loadInterferenceFeatures(
            RegClassInfo.getNumAllocatableRegs(MRI->getRegClass(VirtReg.reg())) <
                RegClassInfo.getNumAllocatableRegs(
                    MRI->getRegClass(Intf->reg())));
-      // Only evict older cascades or live ranges without a cascade.
+
       unsigned IntfCascade = RA.getExtraInfo().getCascade(Intf->reg());
+      // There is a potential that the model could be adversarial and
+      // continually evict live ranges over and over again, leading to a
+      // large amount of compile time being spent in regalloc. If we hit the
+      // threshold, prevent the range from being evicted. We still let the
+      // range through if it is urgent as we are required to produce an
+      // eviction if the candidate is not spillable.
+      if (IntfCascade >= MaxCascade && !Urgent)
+        return false;
+
+      // Only evict older cascades or live ranges without a cascade.
       if (Cascade <= IntfCascade) {
         if (!Urgent)
           return false;