Reland - Arm64: Ensure that csp is always aligned to 16 byte values even if jssp is not.

test/cctest/test-assembler-arm64.cc

Index: test/cctest/test-assembler-arm64.cc
diff --git a/test/cctest/test-assembler-arm64.cc b/test/cctest/test-assembler-arm64.cc
index 25f3adb502da94019ff3565101559016173d9311..1ce900b3f3e90b6a78727d1a64d4ea40867818df 100644
--- a/test/cctest/test-assembler-arm64.cc
+++ b/test/cctest/test-assembler-arm64.cc
@@ -8384,10 +8384,10 @@ static void PushPopJsspSimpleHelper(int reg_count,
 
   START();
 
-  // Registers x8 and x9 are used by the macro assembler for debug code (for
+  // Registers ip0 and ip1 are used by the macro assembler for debug code (for
   // example in 'Pop'), so we can't use them here. We can't use jssp because it
   // will be the stack pointer for this test.
-  static RegList const allowed = ~(x8.Bit() | x9.Bit() | jssp.Bit());
+  static RegList const allowed = ~(ip0.Bit() | ip1.Bit() | jssp.Bit());

[rmcilroy, 2014/05/09 11:18:46]

One last change required here - I think this is a leftover from when you were
using x8/x9 instead of ip0/ip1 as default tmp registers.

[jbramley, 2014/05/09 11:23:51]

We used x8/x9 _and_ ip0/ip1: ip0/ip1 were for general MacroAssembler utilities,
and x8/x9 were used in debug code only (and rarely). Since it worked before, we
should be able to remove them from this mask entirely. It might be a good idea
to clear TmpList() to be safe.

[rmcilroy, 2014/05/09 11:30:56]

The reason this fails now without this change is because a tmp from tmplist (ip0
or ip1) will be used to align csp during the push/pops.  I could clear Tmplist
and remove these from mask such that it falls back to the no-tmp available
branch in BumpSystemStackPointer -  would you prefer I did this?

   if (reg_count == kPushPopJsspMaxRegCount) {
     reg_count = CountSetBits(allowed, kNumberOfRegisters);
   }