Reapply "Lazy deopt without code patching."

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
diff --git a/runtime/vm/stub_code_x64.cc b/runtime/vm/stub_code_x64.cc
index 6ec5ba1e7f37ba76a88702b1107cadf6d3094c0a..ca1ce140f0d3e36a7329812a030190298c368bc0 100644
--- a/runtime/vm/stub_code_x64.cc
+++ b/runtime/vm/stub_code_x64.cc
@@ -497,31 +497,25 @@ static void GenerateDeoptimizationSequence(Assembler* assembler,
 }
 
 
-// TOS: return address + call-instruction-size (5 bytes).
 // RAX: result, must be preserved
 void StubCode::GenerateDeoptimizeLazyFromReturnStub(Assembler* assembler) {
-  // Correct return address to point just after the call that is being
-  // deoptimized.
-  __ popq(RBX);
-  __ subq(RBX, Immediate(ShortCallPattern::pattern_length_in_bytes()));
   // Push zap value instead of CODE_REG for lazy deopt.
   __ pushq(Immediate(0xf1f1f1f1));
-  __ pushq(RBX);
+  // Return address for "call" to deopt stub.
+  __ pushq(Immediate(0xe1e1e1e1));
+  __ movq(CODE_REG, Address(THR, Thread::lazy_deopt_from_return_stub_offset()));
   GenerateDeoptimizationSequence(assembler, kLazyDeoptFromReturn);
 }
 
 
-// TOS: return address + call-instruction-size (5 bytes).
 // RAX: exception, must be preserved
 // RDX: stacktrace, must be preserved
 void StubCode::GenerateDeoptimizeLazyFromThrowStub(Assembler* assembler) {
-  // Correct return address to point just after the call that is being
-  // deoptimized.
-  __ popq(RBX);
-  __ subq(RBX, Immediate(ShortCallPattern::pattern_length_in_bytes()));
   // Push zap value instead of CODE_REG for lazy deopt.
   __ pushq(Immediate(0xf1f1f1f1));
-  __ pushq(RBX);
+  // Return address for "call" to deopt stub.
+  __ pushq(Immediate(0xe1e1e1e1));
+  __ movq(CODE_REG, Address(THR, Thread::lazy_deopt_from_throw_stub_offset()));
   GenerateDeoptimizationSequence(assembler, kLazyDeoptFromThrow);
 }