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, 13 insertions, 0 deletions

diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index afb995d438..88eba4c4fb 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -5226,9 +5226,22 @@ class HArrayLength : public HExpression<1> {
     return obj == InputAt(0);
   }
 
+  void MarkAsStringLength() { SetPackedFlag<kFlagIsStringLength>(); }
+  bool IsStringLength() const { return GetPackedFlag<kFlagIsStringLength>(); }
+
   DECLARE_INSTRUCTION(ArrayLength);
 
  private:
+  // We treat a String as an array, creating the HArrayLength from String.length()
+  // or String.isEmpty() intrinsic in the instruction simplifier. We can always
+  // determine whether a particular HArrayLength is actually a String.length() by
+  // looking at the type of the input but that requires holding the mutator lock, so
+  // we prefer to use a flag, so that code generators don't need to do the locking.
+  static constexpr size_t kFlagIsStringLength = kNumberOfExpressionPackedBits;
+  static constexpr size_t kNumberOfArrayLengthPackedBits = kFlagIsStringLength + 1;
+  static_assert(kNumberOfArrayLengthPackedBits <= HInstruction::kMaxNumberOfPackedBits,
+                "Too many packed fields.");
+
   DISALLOW_COPY_AND_ASSIGN(HArrayLength);
 };