commit c6eec4bed1b5fc5f541929294f3072e769b30ac8
author Aart Bik <ajcbik@google.com> Thu Mar 29 17:22:00 2018 -0700
committer Aart Bik <ajcbik@google.com> Fri Mar 30 10:54:13 2018 -0700
tree 448c055f995c796b2d7d9d404349b85279fd3177
parent 7da5cea7288cd2dc412b1ea3568a800baeab778e

Eliminate redundant abs on zero extension

Bug: b/74026074

Test: test-art-host,target

Change-Id: Ic97c866e3843cd172dfae9652104efe33fced8e5

compiler/optimizing/data_type.h

diff --git a/compiler/optimizing/data_type.h b/compiler/optimizing/data_type.h
index 4a6c914..be26e67 100644
--- a/compiler/optimizing/data_type.h
+++ b/compiler/optimizing/data_type.h
@@ -210,6 +210,12 @@
   static bool IsTypeConversionImplicit(Type input_type, Type result_type);
   static bool IsTypeConversionImplicit(int64_t value, Type result_type);
 
+  static bool IsZeroExtension(Type input_type, Type result_type) {
+    return IsIntOrLongType(result_type) &&
+        IsUnsignedType(input_type) &&
+        Size(result_type) > Size(input_type);
+  }
+
   static const char* PrettyDescriptor(Type type);
 
  private:

compiler/optimizing/instruction_simplifier.cc

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 676fe6b..da37037 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -67,7 +67,6 @@
   bool TryCombineVecMultiplyAccumulate(HVecMul* mul);
 
   void VisitShift(HBinaryOperation* shift);
-
   void VisitEqual(HEqual* equal) OVERRIDE;
   void VisitNotEqual(HNotEqual* equal) OVERRIDE;
   void VisitBooleanNot(HBooleanNot* bool_not) OVERRIDE;
@@ -78,6 +77,7 @@
   void VisitNullCheck(HNullCheck* instruction) OVERRIDE;
   void VisitArrayLength(HArrayLength* instruction) OVERRIDE;
   void VisitCheckCast(HCheckCast* instruction) OVERRIDE;
+  void VisitAbs(HAbs* instruction) OVERRIDE;
   void VisitAdd(HAdd* instruction) OVERRIDE;
   void VisitAnd(HAnd* instruction) OVERRIDE;
   void VisitCondition(HCondition* instruction) OVERRIDE;
@@ -1241,6 +1241,17 @@
   }
 }
 
+void InstructionSimplifierVisitor::VisitAbs(HAbs* instruction) {
+  HInstruction* input = instruction->GetInput();
+  if (DataType::IsZeroExtension(input->GetType(), instruction->GetResultType())) {
+    // Zero extension from narrow to wide can never set sign bit in the wider
+    // operand, making the subsequent Abs redundant (e.g., abs(b & 0xff) for byte b).
+    instruction->ReplaceWith(input);
+    instruction->GetBlock()->RemoveInstruction(instruction);
+    RecordSimplification();
+  }
+}
+
 void InstructionSimplifierVisitor::VisitAdd(HAdd* instruction) {
   HConstant* input_cst = instruction->GetConstantRight();
   HInstruction* input_other = instruction->GetLeastConstantLeft();