Make CTX allocatable by the register allocator.

runtime/vm/stub_code_ia32.cc

Index: runtime/vm/stub_code_ia32.cc
===================================================================
--- runtime/vm/stub_code_ia32.cc	(revision 41279)
+++ runtime/vm/stub_code_ia32.cc	(working copy)
@@ -54,29 +54,10 @@
   __ movl(Address(EAX, Isolate::top_exit_frame_info_offset()), ESP);
 
 #if defined(DEBUG)
-  if (FLAG_verify_incoming_contexts) {
-    Label ok;
-    // Check that the isolate's saved ctx is null.
-    const Immediate& raw_null =
-        Immediate(reinterpret_cast<intptr_t>(Object::null()));
-    __ cmpl(Address(EAX, Isolate::top_context_offset()), raw_null);
-    __ j(EQUAL, &ok, Assembler::kNearJump);
-    __ Stop("Found non-null incoming top context: call to runtime stub");
-    __ Bind(&ok);
-  }
-#endif
-
-  // Save current Context pointer into Isolate structure.
-  __ movl(Address(EAX, Isolate::top_context_offset()), CTX);
-
-  // Cache Isolate pointer into CTX while executing runtime code.
-  __ movl(CTX, EAX);
-
-#if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ movl(EAX, Address(CTX, Isolate::vm_tag_offset()));
-    __ cmpl(EAX, Immediate(VMTag::kDartTagId));
+    __ cmpl(Address(EAX, Isolate::vm_tag_offset()),
+            Immediate(VMTag::kDartTagId));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
@@ -84,7 +65,7 @@
 #endif
 
   // Mark that the isolate is executing VM code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()), ECX);
+  __ movl(Address(EAX, Isolate::vm_tag_offset()), ECX);
 
   // Reserve space for arguments and align frame before entering C++ world.
   __ AddImmediate(ESP, Immediate(-INT32_SIZEOF(NativeArguments)));
@@ -93,7 +74,7 @@
   }
 
   // Pass NativeArguments structure by value and call runtime.
-  __ movl(Address(ESP, isolate_offset), CTX);  // Set isolate in NativeArgs.
+  __ movl(Address(ESP, isolate_offset), EAX);  // Set isolate in NativeArgs.
   // There are no runtime calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
   __ movl(Address(ESP, argc_tag_offset), EDX);  // Set argc in NativeArguments.
@@ -104,23 +85,13 @@
   __ call(ECX);
 
   // Mark that the isolate is executing Dart code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()),
+  __ LoadIsolate(EAX);
+  __ movl(Address(EAX, Isolate::vm_tag_offset()),
           Immediate(VMTag::kDartTagId));
 
   // Reset exit frame information in Isolate structure.
-  __ movl(Address(CTX, Isolate::top_exit_frame_info_offset()), Immediate(0));
+  __ movl(Address(EAX, Isolate::top_exit_frame_info_offset()), Immediate(0));
 
-  // Load Context pointer from Isolate structure into ECX.
-  __ movl(ECX, Address(CTX, Isolate::top_context_offset()));
-
-  // Reset Context pointer in Isolate structure.
-  const Immediate& raw_null =
-      Immediate(reinterpret_cast<intptr_t>(Object::null()));
-  __ movl(Address(CTX, Isolate::top_context_offset()), raw_null);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ movl(CTX, ECX);
-
   __ LeaveFrame();
   __ ret();
 }
@@ -174,30 +145,10 @@
   __ movl(Address(EDI, Isolate::top_exit_frame_info_offset()), ESP);
 
 #if defined(DEBUG)
-  if (FLAG_verify_incoming_contexts) {
-    Label ok;
-    // Check that the isolate's saved ctx is null.
-    const Immediate& raw_null =
-        Immediate(reinterpret_cast<intptr_t>(Object::null()));
-    __ cmpl(Address(EDI, Isolate::top_context_offset()), raw_null);
-    __ j(EQUAL, &ok, Assembler::kNearJump);
-    __ Stop("Found non-null incoming top context: "
-            "call to native c function stub");
-    __ Bind(&ok);
-  }
-#endif
-
-  // Save current Context pointer into Isolate structure.
-  __ movl(Address(EDI, Isolate::top_context_offset()), CTX);
-
-  // Cache Isolate pointer into CTX while executing native code.
-  __ movl(CTX, EDI);
-
-#if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ movl(EDI, Address(CTX, Isolate::vm_tag_offset()));
-    __ cmpl(EDI, Immediate(VMTag::kDartTagId));
+    __ cmpl(Address(EDI, Isolate::vm_tag_offset()),
+            Immediate(VMTag::kDartTagId));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
@@ -205,7 +156,7 @@
 #endif
 
   // Mark that the isolate is executing Native code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()), ECX);
+  __ movl(Address(EDI, Isolate::vm_tag_offset()), ECX);
 
   // Reserve space for the native arguments structure, the outgoing parameters
   // (pointer to the native arguments structure, the C function entry point)
@@ -217,7 +168,7 @@
   }
 
   // Pass NativeArguments structure by value and call native function.
-  __ movl(Address(ESP, isolate_offset), CTX);  // Set isolate in NativeArgs.
+  __ movl(Address(ESP, isolate_offset), EDI);  // Set isolate in NativeArgs.
   __ movl(Address(ESP, argc_tag_offset), EDX);  // Set argc in NativeArguments.
   __ movl(Address(ESP, argv_offset), EAX);  // Set argv in NativeArguments.
   __ leal(EAX, Address(EBP, 2 * kWordSize));  // Compute return value addr.
@@ -229,23 +180,13 @@
   __ call(&NativeEntry::NativeCallWrapperLabel());
 
   // Mark that the isolate is executing Dart code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()),
+  __ LoadIsolate(EDI);
+  __ movl(Address(EDI, Isolate::vm_tag_offset()),
           Immediate(VMTag::kDartTagId));
 
   // Reset exit frame information in Isolate structure.
-  __ movl(Address(CTX, Isolate::top_exit_frame_info_offset()), Immediate(0));
+  __ movl(Address(EDI, Isolate::top_exit_frame_info_offset()), Immediate(0));
 
-  // Load Context pointer from Isolate structure into EDI.
-  __ movl(EDI, Address(CTX, Isolate::top_context_offset()));
-
-  // Reset Context pointer in Isolate structure.
-  const Immediate& raw_null =
-      Immediate(reinterpret_cast<intptr_t>(Object::null()));
-  __ movl(Address(CTX, Isolate::top_context_offset()), raw_null);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ movl(CTX, EDI);
-
   __ LeaveFrame();
   __ ret();
 }
@@ -278,30 +219,10 @@
   __ movl(Address(EDI, Isolate::top_exit_frame_info_offset()), ESP);
 
 #if defined(DEBUG)
-  if (FLAG_verify_incoming_contexts) {
-    Label ok;
-    // Check that the isolate's saved ctx is null.
-    const Immediate& raw_null =
-        Immediate(reinterpret_cast<intptr_t>(Object::null()));
-    __ cmpl(Address(EDI, Isolate::top_context_offset()), raw_null);
-    __ j(EQUAL, &ok, Assembler::kNearJump);
-    __ Stop("Found non-null incoming top context: "
-            "call to bootstrap c function stub");
-    __ Bind(&ok);
-  }
-#endif
-
-  // Save current Context pointer into Isolate structure.
-  __ movl(Address(EDI, Isolate::top_context_offset()), CTX);
-
-  // Cache Isolate pointer into CTX while executing native code.
-  __ movl(CTX, EDI);
-
-#if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ movl(EDI, Address(CTX, Isolate::vm_tag_offset()));
-    __ cmpl(EDI, Immediate(VMTag::kDartTagId));
+    __ cmpl(Address(EDI, Isolate::vm_tag_offset()),
+            Immediate(VMTag::kDartTagId));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
@@ -309,7 +230,7 @@
 #endif
 
   // Mark that the isolate is executing Native code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()), ECX);
+  __ movl(Address(EDI, Isolate::vm_tag_offset()), ECX);
 
   // Reserve space for the native arguments structure, the outgoing parameter
   // (pointer to the native arguments structure) and align frame before
@@ -320,7 +241,7 @@
   }
 
   // Pass NativeArguments structure by value and call native function.
-  __ movl(Address(ESP, isolate_offset), CTX);  // Set isolate in NativeArgs.
+  __ movl(Address(ESP, isolate_offset), EDI);  // Set isolate in NativeArgs.
   __ movl(Address(ESP, argc_tag_offset), EDX);  // Set argc in NativeArguments.
   __ movl(Address(ESP, argv_offset), EAX);  // Set argv in NativeArguments.
   __ leal(EAX, Address(EBP, 2 * kWordSize));  // Compute return value addr.
@@ -330,23 +251,13 @@
   __ call(ECX);
 
   // Mark that the isolate is executing Dart code.
-  __ movl(Address(CTX, Isolate::vm_tag_offset()),
+  __ LoadIsolate(EDI);

[Vyacheslav Egorov (Google), 2014/10/28 13:44:58]

no need to reload, EDI and ESI are both callee save.

[Florian Schneider, 2014/10/28 19:04:31]

Done.

+  __ movl(Address(EDI, Isolate::vm_tag_offset()),
           Immediate(VMTag::kDartTagId));
 
   // Reset exit frame information in Isolate structure.
-  __ movl(Address(CTX, Isolate::top_exit_frame_info_offset()), Immediate(0));
+  __ movl(Address(EDI, Isolate::top_exit_frame_info_offset()), Immediate(0));
 
-  // Load Context pointer from Isolate structure into EDI.
-  __ movl(EDI, Address(CTX, Isolate::top_context_offset()));
-
-  // Reset Context pointer in Isolate structure.
-  const Immediate& raw_null =
-      Immediate(reinterpret_cast<intptr_t>(Object::null()));
-  __ movl(Address(CTX, Isolate::top_context_offset()), raw_null);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ movl(CTX, EDI);
-
   __ LeaveFrame();
   __ ret();
 }
@@ -795,13 +706,7 @@
   __ pushl(ESI);
   __ pushl(EDI);
 
-  // The new Context structure contains a pointer to the current Isolate
-  // structure. Cache the Context pointer in the CTX register so that it is
-  // available in generated code and calls to Isolate::Current() need not be
-  // done. The assumption is that this register will never be clobbered by
-  // compiled or runtime stub code.
-
-  // Cache the new Context pointer into CTX while executing dart code.
+  // Pass the new Context pointer in CTX while executing dart code.
   __ movl(CTX, Address(EBP, kNewContextOffset));
   __ movl(CTX, Address(CTX, VMHandles::kOffsetOfRawPtrInHandle));
 
@@ -825,29 +730,6 @@
   __ pushl(EDX);
   __ movl(Address(EDI, Isolate::top_exit_frame_info_offset()), Immediate(0));
 
-  // Save the old Context pointer. Use ECX as a temporary register.
-  // Note that VisitObjectPointers will find this saved Context pointer during
-  // GC marking, since it traverses any information between SP and
-  // FP - kExitLinkSlotFromEntryFp.
-  // EntryFrame::SavedContext reads the context saved in this frame.
-  // The constant kSavedContextSlotFromEntryFp must be kept in sync with
-  // the code below.
-  ASSERT(kSavedContextSlotFromEntryFp == -6);
-  __ movl(ECX, Address(EDI, Isolate::top_context_offset()));
-  __ pushl(ECX);
-
-  // TODO(turnidge): This code should probably be emitted all the time
-  // on all architectures but I am leaving it under DEBUG/flag for
-  // now.
-#if defined(DEBUG)
-  if (FLAG_verify_incoming_contexts) {
-    // Clear Context pointer in Isolate structure.
-    const Immediate& raw_null =
-        Immediate(reinterpret_cast<intptr_t>(Object::null()));
-    __ movl(Address(EDI, Isolate::top_context_offset()), raw_null);
-  }
-#endif
-
   // Load arguments descriptor array into EDX.
   __ movl(EDX, Address(EBP, kArgumentsDescOffset));
   __ movl(EDX, Address(EDX, VMHandles::kOffsetOfRawPtrInHandle));
@@ -891,17 +773,12 @@
   // Get rid of arguments pushed on the stack.
   __ leal(ESP, Address(ESP, EDX, TIMES_2, 0));  // EDX is a Smi.
 
-  // Load Isolate pointer into CTX. Drop Context.
-  __ LoadIsolate(CTX);
-
-  // Restore the saved Context pointer into the Isolate structure.
-  __ popl(Address(CTX, Isolate::top_context_offset()));
-
   // Restore the saved top exit frame info back into the Isolate structure.
-  __ popl(Address(CTX, Isolate::top_exit_frame_info_offset()));
+  __ LoadIsolate(EDI);
+  __ popl(Address(EDI, Isolate::top_exit_frame_info_offset()));
 
   // Restore the current VMTag from the stack.
-  __ popl(Address(CTX, Isolate::vm_tag_offset()));
+  __ popl(Address(EDI, Isolate::vm_tag_offset()));
 
   // Restore C++ ABI callee-saved registers.
   __ popl(EDI);
@@ -1409,7 +1286,6 @@
   }
 #endif  // DEBUG
 
-  // Check single stepping.
   Label stepping, done_stepping;
   uword single_step_address = reinterpret_cast<uword>(Isolate::Current()) +
       Isolate::single_step_offset();