ARM: Don't generate memory instructions with writeback where the data and address registers are the…

runtime/vm/stub_code_arm.cc

 // Copyright (c) 2013, 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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 419 matching lines @@
 
   // Push registers in their enumeration order: lowest register number at
   // lowest address.
   for (intptr_t i = kNumberOfCpuRegisters - 1; i >= 0; --i) {
     if (i == CODE_REG) {
       // Save the original value of CODE_REG pushed before invoking this stub
       // instead of the value used to call this stub.
       COMPILE_ASSERT(IP > CODE_REG);  // Assert IP is pushed first.
       __ ldr(IP, Address(FP, kCallerSpSlotFromFp * kWordSize));
       __ Push(IP);
+    } else if (i == SP) {
+      // Push(SP) has unpredictable behavior.
+      __ mov(IP, Operand(SP));

[zra, 2015/11/12 20:37:48]

Does this clobber IP before it has been saved? Does IP need to be saved? The
CODE_REG case seems to be worried about that.

[rmacnak, 2015/11/12 21:15:52]

Hm, this does clobber IP before it has been saved.

Florian, does deopt ever use the saved value of IP? Isn't IP also potentially
clobbered by the call to this stub if the stub is at large pool offset?

[Florian Schneider, 2015/11/13 09:04:06]

IP holds the live value of LR at entry where they are swapped - so the assert
above is overly strict and can be removed.
IP will hold the return address which is stored in the frame on EnterFrame, so
it does not matter.

[rmacnak, 2015/11/13 20:09:12]

Removing the assert for the CODE case.

+      __ Push(IP);
     } else {
       __ Push(static_cast<Register>(i));
     }
   }
 
   if (TargetCPUFeatures::vfp_supported()) {
     ASSERT(kFpuRegisterSize == 4 * kWordSize);
     if (kNumberOfDRegisters > 16) {
       __ vstmd(DB_W, SP, D16, kNumberOfDRegisters - 16);
       __ vstmd(DB_W, SP, D0, 16);
@@ skipping 1685 matching lines @@
   __ Bind(&miss);
   __ LoadIsolate(R2);
   __ ldr(CODE_REG, Address(R2, Isolate::ic_miss_code_offset()));
   __ ldr(R1, FieldAddress(CODE_REG, Code::entry_point_offset()));
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM