Intrinsify String.length() and String.isEmpty() as HIR.

Use HArrayLength for String.length() in anticipation of
changing the String.charAt() to HBoundsCheck+HArrayGet to
allow the existing BCE to seamlessly work for strings.
Use HArrayLength+HEqual for String.isEmpty().

We previously relied on inlining but we now want to apply
the new intrinsics even when we do not inline, i.e. when
compiling debuggable (as is currently the case for boot
image) or when we hit inlining limits, i.e. depth, size,
or the number of accumulated dex registers.

Bug: 28330359
Change-Id: Iab9d2f6d2967bdd930a72eb461f27efe8f37c103

1 files changed, 26 insertions, 0 deletions

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index d7b3856bf4..fd79901ffc 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 SimplifyStringIsEmptyOrLength(HInvoke* invoke);
   void SimplifyMemBarrier(HInvoke* invoke, MemBarrierKind barrier_kind);
 
   OptimizingCompilerStats* stats_;
@@ -1673,6 +1674,27 @@ void InstructionSimplifierVisitor::SimplifyFP2Int(HInvoke* invoke) {
   invoke->ReplaceWithExceptInReplacementAtIndex(select, 0);  // false at index 0
 }
 
+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();
+  HInstruction* replacement;
+  if (invoke->GetIntrinsic() == Intrinsics::kStringIsEmpty) {
+    // For String.isEmpty(), create the `HEqual` representing the `length == 0`.
+    invoke->GetBlock()->InsertInstructionBefore(length, invoke);
+    HIntConstant* zero = GetGraph()->GetIntConstant(0);
+    HEqual* equal = new (GetGraph()->GetArena()) HEqual(length, zero, dex_pc);
+    replacement = equal;
+  } else {
+    DCHECK_EQ(invoke->GetIntrinsic(), Intrinsics::kStringLength);
+    replacement = length;
+  }
+  invoke->GetBlock()->ReplaceAndRemoveInstructionWith(invoke, replacement);
+}
+
 void InstructionSimplifierVisitor::SimplifyMemBarrier(HInvoke* invoke, MemBarrierKind barrier_kind) {
   uint32_t dex_pc = invoke->GetDexPc();
   HMemoryBarrier* mem_barrier = new (GetGraph()->GetArena()) HMemoryBarrier(barrier_kind, dex_pc);
@@ -1719,6 +1741,10 @@ void InstructionSimplifierVisitor::VisitInvoke(HInvoke* instruction) {
     case Intrinsics::kDoubleDoubleToLongBits:
       SimplifyFP2Int(instruction);
       break;
+    case Intrinsics::kStringIsEmpty:
+    case Intrinsics::kStringLength:
+      SimplifyStringIsEmptyOrLength(instruction);
+      break;
     case Intrinsics::kUnsafeLoadFence:
       SimplifyMemBarrier(instruction, MemBarrierKind::kLoadAny);
       break;