Convert diamond shaped control flow into a single conditional instruction.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
diff --git a/runtime/vm/assembler_x64.cc b/runtime/vm/assembler_x64.cc
index ec43f5d7921ae6ee00ac388a28cecea0a895ef02..1c259188378a0f55ebf7808b3aeb3f8747787a77 100644
--- a/runtime/vm/assembler_x64.cc
+++ b/runtime/vm/assembler_x64.cc
@@ -155,6 +155,14 @@ void Assembler::popq(const Address& address) {
 }
 
 
+void Assembler::setcc(Condition condition, ByteRegister dst) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0x0F);
+  EmitUint8(0x90 + condition);
+  EmitUint8(0xC0 + dst);
+}
+
+
 void Assembler::movl(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   Operand operand(src);