A64: Add LSubS instruction.

src/a64/lithium-a64.h

Index: src/a64/lithium-a64.h
diff --git a/src/a64/lithium-a64.h b/src/a64/lithium-a64.h
index 14a9e0e3af71e56beb4c85d4fc8261fcb4e991bf..b665bd3be9e40d85e9054f097ab2567faff707bb 100644
--- a/src/a64/lithium-a64.h
+++ b/src/a64/lithium-a64.h
@@ -179,6 +179,7 @@ class LCodeGen;
   V(StringCharFromCode)                         \
   V(StringCompareAndBranch)                     \
   V(SubI)                                       \
+  V(SubS)                                       \
   V(TaggedToI)                                  \
   V(ThisFunction)                               \
   V(Throw)                                      \
@@ -2516,6 +2517,21 @@ class LSubI: public LTemplateInstruction<1, 2, 0> {
 };
 
 
+class LSubS: public LTemplateInstruction<1, 2, 0> {
+ public:
+  LSubS(LOperand* left, LOperand* right) {
+    inputs_[0] = left;
+    inputs_[1] = right;
+  }
+
+  LOperand* left() { return inputs_[0]; }
+  LOperand* right() { return inputs_[1]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(SubS, "sub-s")
+  DECLARE_HYDROGEN_ACCESSOR(Sub)
+};
+
+
 class LThisFunction: public LTemplateInstruction<1, 0, 0> {
  public:
   DECLARE_CONCRETE_INSTRUCTION(ThisFunction, "this-function")