ARM/ARM64: Fix smashed CODE_REG in intrinsics with InvokeMathCFunctionInstrs.

runtime/vm/runtime_entry_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/runtime_entry.h"
 
 #include "vm/assembler.h"
@@ skipping 34 matching lines @@
 //   R5 : address of the runtime function to call.
 //   R4 : number of arguments to the call.
 void RuntimeEntry::Call(Assembler* assembler, intptr_t argument_count) const {
   if (is_leaf()) {
     ASSERT(argument_count == this->argument_count());
     // Since we are entering C++ code, we must restore the C stack pointer from
     // the stack limit to an aligned value nearer to the top of the stack.
     // We cache the Dart stack pointer and the stack limit in callee-saved
     // registers, then align and call, restoring CSP and SP on return from the
     // call.
-    __ mov(R24, CSP);
+    COMPILE_ASSERT(R23 != CODE_REG);

[Vyacheslav Egorov (Google), 2016/05/25 11:15:31]

It might be good to add a comment here why this matters.

In general I think we need a better way of blocking registers to catch places
like this where we use arbitrary registers, but this is a question for another
refactoring. 

Maybe we should teach graph intensifier to do the magic himself.

[rmacnak, 2016/05/25 16:58:51]

Done.
 

+    COMPILE_ASSERT(R25 != CODE_REG);
+    __ mov(R23, CSP);
     __ mov(R25, SP);
     __ ReserveAlignedFrameSpace(0);
     __ mov(CSP, SP);
     __ ldr(TMP, Address(THR, Thread::OffsetFromThread(this)));
     __ blr(TMP);
     __ mov(SP, R25);
-    __ mov(CSP, R24);
+    __ mov(CSP, R23);
   } else {
     // Argument count is not checked here, but in the runtime entry for a more
     // informative error message.
     __ ldr(R5, Address(THR, Thread::OffsetFromThread(this)));
     __ LoadImmediate(R4, argument_count);
     __ BranchLinkToRuntime();
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64