[turbofan] Recognize sign extension of 8-bit and 16-bit values on arm64.

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index fb1f06a2f3fdd0da4d4f807ff803771c00a4b927..2b8d40917b8f65790f4ea57ea0b4c5778ead4e54 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -416,6 +416,12 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
     case kArm64Mov32:
       __ Mov(i.OutputRegister32(), i.InputRegister32(0));
       break;
+    case kArm64Sxtb32:
+      __ Sxtb(i.OutputRegister32(), i.InputRegister32(0));
+      break;
+    case kArm64Sxth32:
+      __ Sxth(i.OutputRegister32(), i.InputRegister32(0));
+      break;
     case kArm64Sxtw:
       __ Sxtw(i.OutputRegister(), i.InputRegister32(0));
       break;