Make CTX allocatable by the register allocator.

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 26 matching lines @@
   const intptr_t isolate_offset = NativeArguments::isolate_offset();
   const intptr_t argc_tag_offset = NativeArguments::argc_tag_offset();
   const intptr_t argv_offset = NativeArguments::argv_offset();
   const intptr_t retval_offset = NativeArguments::retval_offset();
   const intptr_t exitframe_last_param_slot_from_fp = 1;
 
   __ SetPrologueOffset();
   __ Comment("CallToRuntimeStub");
   __ EnterFrame(0);
 
-  __ LoadIsolate(R0, kNoPP);
+  COMPILE_ASSERT((kAbiPreservedCpuRegs & (1 << R28)) != 0);
+  __ LoadIsolate(R28, kNoPP);
 
   // Save exit frame information to enable stack walking as we are about
   // to transition to Dart VM C++ code.
-  __ StoreToOffset(SP, R0, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Save current Context pointer into Isolate structure.
-  __ StoreToOffset(CTX, R0, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Isolate pointer into CTX while executing runtime code.
-  __ mov(CTX, R0);
+  __ StoreToOffset(SP, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
 #if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ LoadFromOffset(R8, R0, Isolate::vm_tag_offset(), kNoPP);
+    __ LoadFromOffset(R8, R28, Isolate::vm_tag_offset(), kNoPP);
     __ CompareImmediate(R8, VMTag::kDartTagId, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
   }
 #endif
 
   // Mark that the isolate is executing VM code.
-  __ StoreToOffset(R5, R0, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R5, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reserve space for arguments and align frame before entering C++ world.
   // NativeArguments are passed in registers.
   __ Comment("align stack");
   // Reserve space for arguments.
   ASSERT(sizeof(NativeArguments) == 4 * kWordSize);
   __ ReserveAlignedFrameSpace(sizeof(NativeArguments));
 
   // Pass NativeArguments structure by value and call runtime.
   // Registers R0, R1, R2, and R3 are used.
 
   ASSERT(isolate_offset == 0 * kWordSize);
-  // Set isolate in NativeArgs: R0 already contains CTX.
+  // Set isolate in NativeArgs.
+  __ mov(R0, R28);
 
   // There are no runtime calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
   ASSERT(argc_tag_offset == 1 * kWordSize);
   __ mov(R1, R4);  // Set argc in NativeArguments.
 
   ASSERT(argv_offset == 2 * kWordSize);
   __ add(R2, ZR, Operand(R4, LSL, 3));
   __ add(R2, FP, Operand(R2));  // Compute argv.
   // Set argv in NativeArguments.
@@ skipping 17 matching lines @@
   __ blr(R5);
   __ Comment("CallToRuntimeStub return");
 
   // Restore SP and CSP.
   __ mov(SP, CSP);
   __ mov(CSP, R26);
 
   // Retval is next to 1st argument.
   // Mark that the isolate is executing Dart code.
   __ LoadImmediate(R2, VMTag::kDartTagId, kNoPP);
-  __ StoreToOffset(R2, CTX, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R2, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reset exit frame information in Isolate structure.
-  __ StoreToOffset(ZR, CTX, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Load Context pointer from Isolate structure into A2.
-  __ LoadFromOffset(R2, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Load null.
-  __ LoadObject(TMP, Object::null_object(), PP);
-
-  // Reset Context pointer in Isolate structure.
-  __ StoreToOffset(TMP, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ mov(CTX, R2);
+  __ StoreToOffset(ZR, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
   __ LeaveFrame();
   __ ret();
 }
 
 
 void StubCode::GeneratePrintStopMessageStub(Assembler* assembler) {
   __ Stop("GeneratePrintStopMessageStub");
 }
 
 
 // Input parameters:
 //   LR : return address.
 //   SP : address of return value.
 //   R5 : address of the native function to call.
 //   R2 : address of first argument in argument array.
 //   R1 : argc_tag including number of arguments and function kind.
 void StubCode::GenerateCallNativeCFunctionStub(Assembler* assembler) {
   const intptr_t isolate_offset = NativeArguments::isolate_offset();
   const intptr_t argc_tag_offset = NativeArguments::argc_tag_offset();
   const intptr_t argv_offset = NativeArguments::argv_offset();
   const intptr_t retval_offset = NativeArguments::retval_offset();
 
   __ EnterFrame(0);
 
-  __ LoadIsolate(R0, kNoPP);
+  COMPILE_ASSERT((kAbiPreservedCpuRegs & (1 << R28)) != 0);
+  __ LoadIsolate(R28, kNoPP);
 
   // Save exit frame information to enable stack walking as we are about
   // to transition to native code.
-  __ StoreToOffset(SP, R0, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Save current Context pointer into Isolate structure.
-  __ StoreToOffset(CTX, R0, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Isolate pointer into CTX while executing native code.
-  __ mov(CTX, R0);
+  __ StoreToOffset(SP, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
 #if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ LoadFromOffset(R6, CTX, Isolate::vm_tag_offset(), kNoPP);
+    __ LoadFromOffset(R6, R28, Isolate::vm_tag_offset(), kNoPP);
     __ CompareImmediate(R6, VMTag::kDartTagId, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
   }
 #endif
 
   // Mark that the isolate is executing Native code.
-  __ StoreToOffset(R5, CTX, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R5, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reserve space for the native arguments structure passed on the stack (the
   // outgoing pointer parameter to the native arguments structure is passed in
   // R0) and align frame before entering the C++ world.
   __ ReserveAlignedFrameSpace(sizeof(NativeArguments));
 
   // Initialize NativeArguments structure and call native function.
   // Registers R0, R1, R2, and R3 are used.
 
   ASSERT(isolate_offset == 0 * kWordSize);
-  // Set isolate in NativeArgs: R0 already contains CTX.
+  // Set isolate in NativeArgs.
+  __ mov(R0, R28);
 
   // There are no native calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
   ASSERT(argc_tag_offset == 1 * kWordSize);
   // Set argc in NativeArguments: R1 already contains argc.
 
   ASSERT(argv_offset == 2 * kWordSize);
   // Set argv in NativeArguments: R2 already contains argv.
 
   // Set retval in NativeArgs.
@@ skipping 26 matching lines @@
 #else
   __ BranchLink(&NativeEntry::NativeCallWrapperLabel(), kNoPP);
 #endif
 
   // Restore SP and CSP.
   __ mov(SP, CSP);
   __ mov(CSP, R26);
 
   // Mark that the isolate is executing Dart code.
   __ LoadImmediate(R2, VMTag::kDartTagId, kNoPP);
-  __ StoreToOffset(R2, CTX, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R2, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reset exit frame information in Isolate structure.
-  __ StoreToOffset(ZR, CTX, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Load Context pointer from Isolate structure into R2.
-  __ LoadFromOffset(R2, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Reset Context pointer in Isolate structure.
-  __ LoadObject(R3, Object::null_object(), PP);
-  __ StoreToOffset(R3, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ mov(CTX, R2);
+  __ StoreToOffset(ZR, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
   __ LeaveFrame();
   __ ret();
 }
 
 
 // Input parameters:
 //   LR : return address.
 //   SP : address of return value.
 //   R5 : address of the native function to call.
 //   R2 : address of first argument in argument array.
 //   R1 : argc_tag including number of arguments and function kind.
 void StubCode::GenerateCallBootstrapCFunctionStub(Assembler* assembler) {
   const intptr_t isolate_offset = NativeArguments::isolate_offset();
   const intptr_t argc_tag_offset = NativeArguments::argc_tag_offset();
   const intptr_t argv_offset = NativeArguments::argv_offset();
   const intptr_t retval_offset = NativeArguments::retval_offset();
 
   __ EnterFrame(0);
 
-  __ LoadIsolate(R0, kNoPP);
+  COMPILE_ASSERT((kAbiPreservedCpuRegs & (1 << R28)) != 0);
+  __ LoadIsolate(R28, kNoPP);
 
   // Save exit frame information to enable stack walking as we are about
   // to transition to native code.
-  __ StoreToOffset(SP, R0, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Save current Context pointer into Isolate structure.
-  __ StoreToOffset(CTX, R0, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Isolate pointer into CTX while executing native code.
-  __ mov(CTX, R0);
+  __ StoreToOffset(SP, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
 #if defined(DEBUG)
   { Label ok;
     // Check that we are always entering from Dart code.
-    __ LoadFromOffset(R6, CTX, Isolate::vm_tag_offset(), kNoPP);
+    __ LoadFromOffset(R6, R28, Isolate::vm_tag_offset(), kNoPP);
     __ CompareImmediate(R6, VMTag::kDartTagId, kNoPP);
     __ b(&ok, EQ);
     __ Stop("Not coming from Dart code.");
     __ Bind(&ok);
   }
 #endif
 
   // Mark that the isolate is executing Native code.
-  __ StoreToOffset(R5, CTX, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R5, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reserve space for the native arguments structure passed on the stack (the
   // outgoing pointer parameter to the native arguments structure is passed in
   // R0) and align frame before entering the C++ world.
   __ ReserveAlignedFrameSpace(sizeof(NativeArguments));
 
   // Initialize NativeArguments structure and call native function.
   // Registers R0, R1, R2, and R3 are used.
 
   ASSERT(isolate_offset == 0 * kWordSize);
-  // Set isolate in NativeArgs: R0 already contains CTX.
+  // Set isolate in NativeArgs.
+  __ mov(R0, R28);
 
   // There are no native calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
   ASSERT(argc_tag_offset == 1 * kWordSize);
   // Set argc in NativeArguments: R1 already contains argc.
 
   ASSERT(argv_offset == 2 * kWordSize);
   // Set argv in NativeArguments: R2 already contains argv.
 
   // Set retval in NativeArgs.
@@ skipping 17 matching lines @@
 
   // Call native function or redirection via simulator.
   __ blr(R5);
 
   // Restore SP and CSP.
   __ mov(SP, CSP);
   __ mov(CSP, R26);
 
   // Mark that the isolate is executing Dart code.
   __ LoadImmediate(R2, VMTag::kDartTagId, kNoPP);
-  __ StoreToOffset(R2, CTX, Isolate::vm_tag_offset(), kNoPP);
+  __ StoreToOffset(R2, R28, Isolate::vm_tag_offset(), kNoPP);
 
   // Reset exit frame information in Isolate structure.
-  __ StoreToOffset(ZR, CTX, Isolate::top_exit_frame_info_offset(), kNoPP);
-
-  // Load Context pointer from Isolate structure into R2.
-  __ LoadFromOffset(R2, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Reset Context pointer in Isolate structure.
-  __ LoadObject(R3, Object::null_object(), PP);
-  __ StoreToOffset(R3, CTX, Isolate::top_context_offset(), kNoPP);
-
-  // Cache Context pointer into CTX while executing Dart code.
-  __ mov(CTX, R2);
+  __ StoreToOffset(ZR, R28, Isolate::top_exit_frame_info_offset(), kNoPP);
 
   __ LeaveFrame();
   __ ret();
 }
 
 
 // Input parameters:
 //   R4: arguments descriptor array.
 void StubCode::GenerateCallStaticFunctionStub(Assembler* assembler) {
   // Create a stub frame as we are pushing some objects on the stack before
@@ skipping 450 matching lines @@
     // C++ code.
     __ str(r, Address(SP, -1 * kWordSize, Address::PreIndex));
   }
 
   // Save the bottom 64-bits of callee-saved V registers.
   for (int i = kAbiFirstPreservedFpuReg; i <= kAbiLastPreservedFpuReg; i++) {
     const VRegister r = static_cast<VRegister>(i);
     __ PushDouble(r);
   }
 
-  // Push new context.
-  __ Push(R3);
-#if defined(DEBUG)
-  {
-    Label ok;
-    // The new context, saved vm tag, the top exit frame, and the old context.
-    const intptr_t kNewContextOffsetFromFp =
-        -(1 + kAbiPreservedCpuRegCount + kAbiPreservedFpuRegCount) * kWordSize;
-    __ AddImmediate(R4, FP, kNewContextOffsetFromFp, kNoPP);
-    __ CompareRegisters(R4, SP);
-    __ b(&ok, EQ);
-    __ Stop("kNewContextOffsetFromFp mismatch");
-    __ Bind(&ok);
-  }
-#endif
-
   // We now load the pool pointer(PP) as we are about to invoke dart code and we
   // could potentially invoke some intrinsic functions which need the PP to be
   // set up.
   __ LoadPoolPointer(PP);
 
-  // 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.
-  __ LoadFromOffset(CTX, R3, VMHandles::kOffsetOfRawPtrInHandle, PP);
-
   // Load Isolate pointer into temporary register R5.
   __ LoadIsolate(R5, PP);
 
   // Save the current VMTag on the stack.
-  ASSERT(kSavedVMTagSlotFromEntryFp == -20);
   __ LoadFromOffset(R4, R5, Isolate::vm_tag_offset(), PP);
   __ Push(R4);
 
   // Mark that the isolate is executing Dart code.
   __ LoadImmediate(R6, VMTag::kDartTagId, PP);
   __ StoreToOffset(R6, R5, Isolate::vm_tag_offset(), PP);
 
   // Save the top exit frame info. Use R6 as a temporary register.
   // StackFrameIterator reads the top exit frame info saved in this frame.
   __ LoadFromOffset(R6, R5, Isolate::top_exit_frame_info_offset(), PP);
   __ StoreToOffset(ZR, R5, Isolate::top_exit_frame_info_offset(), PP);
 
-  // Save the old Context pointer. Use R4 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.
-  __ LoadFromOffset(R4, R5, Isolate::top_context_offset(), PP);
-
-  // The constants kSavedContextSlotFromEntryFp and
   // kExitLinkSlotFromEntryFp must be kept in sync with the code below.
-  ASSERT(kExitLinkSlotFromEntryFp == -21);
-  ASSERT(kSavedContextSlotFromEntryFp == -22);
+  ASSERT(kExitLinkSlotFromEntryFp == -20);
   __ Push(R6);
-  __ Push(R4);
 
   // Load arguments descriptor array into R4, which is passed to Dart code.
   __ LoadFromOffset(R4, R1, VMHandles::kOffsetOfRawPtrInHandle, PP);
 
   // Load number of arguments into S5.
   __ LoadFieldFromOffset(R5, R4, ArgumentsDescriptor::count_offset(), PP);
   __ SmiUntag(R5);
 
   // Compute address of 'arguments array' data area into R2.
   __ LoadFromOffset(R2, R2, VMHandles::kOffsetOfRawPtrInHandle, PP);
@@ skipping 15 matching lines @@
   __ Bind(&done_push_arguments);
 
   // Call the Dart code entrypoint.
   __ blr(R0);  // R4 is the arguments descriptor array.
   __ Comment("InvokeDartCodeStub return");
 
   // Restore constant pool pointer after return.
   __ LoadPoolPointer(PP);
 
   // Get rid of arguments pushed on the stack.
-  __ AddImmediate(SP, FP, kSavedContextSlotFromEntryFp * kWordSize, PP);
+  __ AddImmediate(SP, FP, kExitLinkSlotFromEntryFp * kWordSize, PP);
 
-  // Load Isolate pointer into CTX.
-  __ LoadIsolate(CTX, PP);
+  __ LoadIsolate(R28, PP);
+
+  // Restore the saved top exit frame info back into the Isolate structure.
+  // Uses R6 as a temporary register for this.
+  __ Pop(R6);
+  __ StoreToOffset(R6, R28, Isolate::top_exit_frame_info_offset(), PP);
 
   // Restore the current VMTag from the stack.
-  __ ldr(R4, Address(SP, 2 * kWordSize));
-  __ StoreToOffset(R4, CTX, Isolate::vm_tag_offset(), PP);
-
-  // Restore the saved Context pointer into the Isolate structure.
-  // Uses R4 as a temporary register for this.
-  // Restore the saved top exit frame info back into the Isolate structure.
-  // Uses R6 as a temporary register for this.
   __ Pop(R4);
-  __ Pop(R6);
-  __ StoreToOffset(R4, CTX, Isolate::top_context_offset(), PP);
-  __ StoreToOffset(R6, CTX, Isolate::top_exit_frame_info_offset(), PP);
-
-  __ Pop(R3);
-  __ Pop(R4);
+  __ StoreToOffset(R4, R28, Isolate::vm_tag_offset(), PP);
 
   // Restore the bottom 64-bits of callee-saved V registers.
   for (int i = kAbiLastPreservedFpuReg; i >= kAbiFirstPreservedFpuReg; i--) {
     const VRegister r = static_cast<VRegister>(i);
     __ PopDouble(r);
   }
 
   // Restore C++ ABI callee-saved registers.
   for (int i = kAbiLastPreservedCpuReg; i >= kAbiFirstPreservedCpuReg; i--) {
     Register r = static_cast<Register>(i);
@@ skipping 1143 matching lines @@
   const Register right = R0;
   __ LoadFromOffset(left, SP, 1 * kWordSize, kNoPP);
   __ LoadFromOffset(right, SP, 0 * kWordSize, kNoPP);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64