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[MLGO] Add Threshold to Prevent Pathological Compile Time Cases #119807

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Merged
merged 1 commit into from
Dec 13, 2024
Merged

[MLGO] Add Threshold to Prevent Pathological Compile Time Cases #119807

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16 changes: 15 additions & 1 deletion llvm/lib/CodeGen/MLRegAllocEvictAdvisor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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"
Expand Down Expand Up @@ -643,8 +649,16 @@ 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.
if (IntfCascade >= MaxCascade)
return false;

// Only evict older cascades or live ranges without a cascade.
if (Cascade <= IntfCascade) {
if (!Urgent)
return false;
Expand Down
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