Replace String.charAt() with HIR.

Replace String.charAt() with HArrayLength, HBoundsCheck and
HArrayGet. This allows GVN on the HArrayLength and BCE on
the HBoundsCheck as well as using the infrastructure for
HArrayGet, i.e. better handling of constant indexes than
the old intrinsic and using the HArm64IntermediateAddress.

Bug: 28330359
Change-Id: I32bf1da7eeafe82537a60416abf6ac412baa80dc

1 files changed, 25 insertions, 2 deletions

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index eb1d1560db..62d637081d 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -101,6 +101,7 @@ class InstructionSimplifierVisitor : public HGraphDelegateVisitor {
   void SimplifyCompare(HInvoke* invoke, bool is_signum, Primitive::Type type);
   void SimplifyIsNaN(HInvoke* invoke);
   void SimplifyFP2Int(HInvoke* invoke);
+  void SimplifyStringCharAt(HInvoke* invoke);
   void SimplifyStringIsEmptyOrLength(HInvoke* invoke);
   void SimplifyMemBarrier(HInvoke* invoke, MemBarrierKind barrier_kind);
 
@@ -1685,13 +1686,32 @@ void InstructionSimplifierVisitor::SimplifyFP2Int(HInvoke* invoke) {
   invoke->ReplaceWithExceptInReplacementAtIndex(select, 0);  // false at index 0
 }
 
+void InstructionSimplifierVisitor::SimplifyStringCharAt(HInvoke* invoke) {
+  HInstruction* str = invoke->InputAt(0);
+  HInstruction* index = invoke->InputAt(1);
+  uint32_t dex_pc = invoke->GetDexPc();
+  ArenaAllocator* arena = GetGraph()->GetArena();
+  // We treat String as an array to allow DCE and BCE to seamlessly work on strings,
+  // so create the HArrayLength, HBoundsCheck and HArrayGet.
+  HArrayLength* length = new (arena) HArrayLength(str, dex_pc, /* is_string_length */ true);
+  invoke->GetBlock()->InsertInstructionBefore(length, invoke);
+  HBoundsCheck* bounds_check =
+      new (arena) HBoundsCheck(index, length, dex_pc, invoke->GetDexMethodIndex());
+  invoke->GetBlock()->InsertInstructionBefore(bounds_check, invoke);
+  HArrayGet* array_get =
+      new (arena) HArrayGet(str, index, Primitive::kPrimChar, dex_pc, /* is_string_char_at */ true);
+  invoke->GetBlock()->ReplaceAndRemoveInstructionWith(invoke, array_get);
+  bounds_check->CopyEnvironmentFrom(invoke->GetEnvironment());
+  GetGraph()->SetHasBoundsChecks(true);
+}
+
 void InstructionSimplifierVisitor::SimplifyStringIsEmptyOrLength(HInvoke* invoke) {
   HInstruction* str = invoke->InputAt(0);
   uint32_t dex_pc = invoke->GetDexPc();
   // We treat String as an array to allow DCE and BCE to seamlessly work on strings,
   // so create the HArrayLength.
-  HArrayLength* length = new (GetGraph()->GetArena()) HArrayLength(str, dex_pc);
-  length->MarkAsStringLength();
+  HArrayLength* length =
+      new (GetGraph()->GetArena()) HArrayLength(str, dex_pc, /* is_string_length */ true);
   HInstruction* replacement;
   if (invoke->GetIntrinsic() == Intrinsics::kStringIsEmpty) {
     // For String.isEmpty(), create the `HEqual` representing the `length == 0`.
@@ -1752,6 +1772,9 @@ void InstructionSimplifierVisitor::VisitInvoke(HInvoke* instruction) {
     case Intrinsics::kDoubleDoubleToLongBits:
       SimplifyFP2Int(instruction);
       break;
+    case Intrinsics::kStringCharAt:
+      SimplifyStringCharAt(instruction);
+      break;
     case Intrinsics::kStringIsEmpty:
     case Intrinsics::kStringLength:
       SimplifyStringIsEmptyOrLength(instruction);