Optimizing: Remove unnecessary And before TypeConversion.

For example `(byte) (x & 0xff)` doesn't need the `& 0xff`.

Bug: 23965701
Change-Id: I5fc8419491aff2cdc7074451e74e873b5f582d41

1 files changed, 18 insertions, 0 deletions

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 98f8009846..a48d06f3d0 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -830,6 +830,24 @@ void InstructionSimplifierVisitor::VisitTypeConversion(HTypeConversion* instruct
         return;
       }
     }
+  } else if (input->IsAnd() &&
+      Primitive::IsIntegralType(result_type) &&
+      input->HasOnlyOneNonEnvironmentUse()) {
+    DCHECK(Primitive::IsIntegralType(input_type));
+    HAnd* input_and = input->AsAnd();
+    HConstant* constant = input_and->GetConstantRight();
+    if (constant != nullptr) {
+      int64_t value = Int64FromConstant(constant);
+      DCHECK_NE(value, -1);  // "& -1" would have been optimized away in VisitAnd().
+      size_t trailing_ones = CTZ(~static_cast<uint64_t>(value));
+      if (trailing_ones >= kBitsPerByte * Primitive::ComponentSize(result_type)) {
+        // The `HAnd` is useless, for example in `(byte) (x & 0xff)`, get rid of it.
+        input_and->ReplaceWith(input_and->GetLeastConstantLeft());
+        input_and->GetBlock()->RemoveInstruction(input_and);
+        RecordSimplification();
+        return;
+      }
+    }
   }
 }