Recognize and optimize a.runtimeType == b.runtimeType pattern.

runtime/vm/assembler_arm.cc

Index: runtime/vm/assembler_arm.cc
diff --git a/runtime/vm/assembler_arm.cc b/runtime/vm/assembler_arm.cc
index e768806218f9d0692675e28bcf3fffddfdc1c0e4..f1b49f03ce34d49ee7c1a29f4a1db87a64795dcd 100644
--- a/runtime/vm/assembler_arm.cc
+++ b/runtime/vm/assembler_arm.cc
@@ -3017,6 +3017,32 @@ void Assembler::SubImmediateSetFlags(Register rd, Register rn, int32_t value,
 }
 
 
+void Assembler::SubImmediate(Register rd, Register rn, int32_t value,
+                             Condition cond) {

[regis, 2016/10/08 09:10:37]

Why do you need this new flavor? Since you are not setting the flags, calling
AddImmediate(rd, rn, -value, cond) should be equivalent.

[Vyacheslav Egorov (Google), 2016/10/24 20:23:02]

Done.

+  Operand o;
+  if (Operand::CanHold(value, &o)) {
+    // Handles value == kMinInt32.
+    sub(rd, rn, o, cond);
+  } else if (Operand::CanHold(-value, &o)) {
+    ASSERT(value != kMinInt32);  // Would cause erroneous overflow detection.
+    add(rd, rn, o, cond);
+  } else {
+    ASSERT(rn != IP);
+    if (Operand::CanHold(~value, &o)) {
+      mvn(IP, o, cond);
+      sub(rd, rn, Operand(IP), cond);
+    } else if (Operand::CanHold(~(-value), &o)) {
+      ASSERT(value != kMinInt32);  // Would cause erroneous overflow detection.
+      mvn(IP, o, cond);
+      add(rd, rn, Operand(IP), cond);
+    } else {
+      LoadDecodableImmediate(IP, value, cond);
+      sub(rd, rn, Operand(IP), cond);
+    }
+  }
+}
+
+
 void Assembler::AndImmediate(Register rd, Register rs, int32_t imm,
                              Condition cond) {
   Operand o;