Constant fold BitCount intrinsic

Bug: 309886589
Test: art/test/testrunner/testrunner.py --host --64 -b --optimizing
Change-Id: Id0db658e1139886b7bffd63431a7cd2d4c75506d

1 files changed, 25 insertions, 0 deletions

diff --git a/compiler/optimizing/constant_folding.cc b/compiler/optimizing/constant_folding.cc
index e2bfffb8ec..29f5d5caee 100644
--- a/compiler/optimizing/constant_folding.cc
+++ b/compiler/optimizing/constant_folding.cc
@@ -59,6 +59,7 @@ class HConstantFoldingVisitor final : public HGraphDelegateVisitor {
   // Intrinsics foldings
   void FoldReverseIntrinsic(HInvoke* invoke);
   void FoldReverseBytesIntrinsic(HInvoke* invoke);
+  void FoldBitCountIntrinsic(HInvoke* invoke);
   void FoldHighestOneBitIntrinsic(HInvoke* invoke);
   void FoldLowestOneBitIntrinsic(HInvoke* invoke);
   void FoldNumberOfLeadingZerosIntrinsic(HInvoke* invoke);
@@ -374,6 +375,10 @@ void HConstantFoldingVisitor::VisitInvoke(HInvoke* inst) {
     case Intrinsics::kShortReverseBytes:
       FoldReverseBytesIntrinsic(inst);
       break;
+    case Intrinsics::kIntegerBitCount:
+    case Intrinsics::kLongBitCount:
+      FoldBitCountIntrinsic(inst);
+      break;
     case Intrinsics::kIntegerHighestOneBit:
     case Intrinsics::kLongHighestOneBit:
       FoldHighestOneBitIntrinsic(inst);
@@ -442,6 +447,26 @@ void HConstantFoldingVisitor::FoldReverseBytesIntrinsic(HInvoke* inst) {
   inst->GetBlock()->RemoveInstruction(inst);
 }
 
+void HConstantFoldingVisitor::FoldBitCountIntrinsic(HInvoke* inst) {
+  DCHECK(inst->GetIntrinsic() == Intrinsics::kIntegerBitCount ||
+         inst->GetIntrinsic() == Intrinsics::kLongBitCount);
+
+  HInstruction* input = inst->InputAt(0);
+  if (!input->IsConstant()) {
+    return;
+  }
+
+  DCHECK_IMPLIES(inst->GetIntrinsic() == Intrinsics::kIntegerBitCount, input->IsIntConstant());
+  DCHECK_IMPLIES(inst->GetIntrinsic() == Intrinsics::kLongBitCount, input->IsLongConstant());
+
+  // Note that both the Integer and Long intrinsics return an int as a result.
+  int result = inst->GetIntrinsic() == Intrinsics::kIntegerBitCount ?
+                   POPCOUNT(input->AsIntConstant()->GetValue()) :
+                   POPCOUNT(input->AsLongConstant()->GetValue());
+  inst->ReplaceWith(GetGraph()->GetIntConstant(result));
+  inst->GetBlock()->RemoveInstruction(inst);
+}
+
 void HConstantFoldingVisitor::FoldHighestOneBitIntrinsic(HInvoke* inst) {
   DCHECK(inst->GetIntrinsic() == Intrinsics::kIntegerHighestOneBit ||
          inst->GetIntrinsic() == Intrinsics::kLongHighestOneBit);