Dart VM: Simplify code generation for equality operators.

runtime/vm/stub_code_ia32.cc

Index: runtime/vm/stub_code_ia32.cc
===================================================================
--- runtime/vm/stub_code_ia32.cc	(revision 27755)
+++ runtime/vm/stub_code_ia32.cc	(working copy)
@@ -2032,105 +2032,6 @@
 }
 
 
-// Implements equality operator when one of the arguments is null
-// (identity check) and updates ICData if necessary.
-// TOS + 0: return address
-// TOS + 1: right argument
-// TOS + 2: left argument
-// ECX: ICData.
-// EAX: result.
-// TODO(srdjan): Move to VM stubs once Boolean objects become VM objects.
-void StubCode::GenerateEqualityWithNullArgStub(Assembler* assembler) {

[hausner, 2013/09/23 16:51:06]

As best as I can tell removing this stub breaks debugging, and doesn't let the
VM collect IC data on arguments.

If you inline the null checks on the AST level, the debugger has no chance to
reach a safe point when one of the arguments is null, since no runtime call and
no method call ever takes place.

[Florian Schneider, 2013/09/23 18:02:37]

I don't see how: == is still a plain method call. It is the callee that is
modified to check at method entry if the other argument is null.

Type feedback is collected like for normal method calls.

All current debugger tests pass. Is there a debugger test that specifically
tests breaking at ==?

-  static const intptr_t kNumArgsTested = 2;
-#if defined(DEBUG)
-  { Label ok;
-    __ movl(EAX, FieldAddress(ECX, ICData::num_args_tested_offset()));
-    __ cmpl(EAX, Immediate(kNumArgsTested));
-    __ j(EQUAL, &ok, Assembler::kNearJump);
-    __ Stop("Incorrect ICData for equality");
-    __ Bind(&ok);
-  }
-#endif  // DEBUG
-  // Check IC data, update if needed.
-  // ECX: IC data object (preserved).
-  __ movl(EBX, FieldAddress(ECX, ICData::ic_data_offset()));
-  // EBX: ic_data_array with check entries: classes and target functions.
-  __ leal(EBX, FieldAddress(EBX, Array::data_offset()));
-  // EBX: points directly to the first ic data array element.
-
-  Label get_class_id_as_smi, no_match, loop, compute_result, found;
-  __ Bind(&loop);
-  // Check left.
-  __ movl(EAX, Address(ESP, 2 * kWordSize));
-  __ call(&get_class_id_as_smi);
-  __ movl(EDI, Address(EBX, 0 * kWordSize));
-  __ cmpl(EAX, EDI);  // Class id match?
-  __ j(NOT_EQUAL, &no_match, Assembler::kNearJump);
-  // Check right.
-  __ movl(EAX, Address(ESP, 1 * kWordSize));
-  __ call(&get_class_id_as_smi);
-  __ movl(EDI, Address(EBX, 1 * kWordSize));
-  __ cmpl(EAX, EDI);  // Class id match?
-  __ j(EQUAL, &found, Assembler::kNearJump);
-  __ Bind(&no_match);
-  // Next check group.
-  __ addl(EBX, Immediate(
-      kWordSize * ICData::TestEntryLengthFor(kNumArgsTested)));
-  __ cmpl(EDI, Immediate(Smi::RawValue(kIllegalCid)));  // Done?
-  __ j(NOT_EQUAL, &loop, Assembler::kNearJump);
-  Label update_ic_data;
-  __ jmp(&update_ic_data);
-
-  __ Bind(&found);
-  const intptr_t count_offset =
-      ICData::CountIndexFor(kNumArgsTested) * kWordSize;
-  __ addl(Address(EBX, count_offset), Immediate(Smi::RawValue(1)));
-  __ j(NO_OVERFLOW, &compute_result);
-  __ movl(Address(EBX, count_offset),
-          Immediate(Smi::RawValue(Smi::kMaxValue)));
-
-  __ Bind(&compute_result);
-  Label true_label;
-  __ movl(EAX, Address(ESP, 1 * kWordSize));
-  __ cmpl(EAX, Address(ESP, 2 * kWordSize));
-  __ j(EQUAL, &true_label, Assembler::kNearJump);
-  __ LoadObject(EAX, Bool::False());
-  __ ret();
-  __ Bind(&true_label);
-  __ LoadObject(EAX, Bool::True());
-  __ ret();
-
-  __ Bind(&get_class_id_as_smi);
-  Label not_smi;
-  // Test if Smi -> load Smi class for comparison.
-  __ testl(EAX, Immediate(kSmiTagMask));
-  __ j(NOT_ZERO, &not_smi, Assembler::kNearJump);
-  __ movl(EAX, Immediate(Smi::RawValue(kSmiCid)));
-  __ ret();
-
-  __ Bind(&not_smi);
-  __ LoadClassId(EAX, EAX);
-  __ SmiTag(EAX);
-  __ ret();
-
-  __ Bind(&update_ic_data);
-
-  // ECX: ICData
-  __ movl(EAX, Address(ESP, 1 * kWordSize));
-  __ movl(EDI, Address(ESP, 2 * kWordSize));
-  __ EnterStubFrame();
-  __ pushl(EDI);  // arg 0
-  __ pushl(EAX);  // arg 1
-  __ PushObject(Symbols::EqualOperator());  // Target's name.
-  __ pushl(ECX);  // ICData
-  __ CallRuntime(kUpdateICDataTwoArgsRuntimeEntry, 4);
-  __ Drop(4);
-  __ LeaveFrame();
-
-  __ jmp(&compute_result, Assembler::kNearJump);
-}
-
-
 // Calls to the runtime to optimize the given function.
 // EDI: function to be reoptimized.
 // EDX: argument descriptor (preserved).