Fixes to support ARMv5 lego mindstorm.

Fixes to support ARMv5 lego mindstorm.

1. Deopts on division when neither vfp nor idiv are present.
   In a subsequent CL, I can add a leaf runtime call for this.

2. Uses a different PC read offset in STR and STM instructions.
   On ARMv5 and earlier, the PC read offset is 8 except in STR
   and STM instructions, where it is implementation defined. On
   lego mindstorm it is 12. This requires changing
   kEntryPointToPcMarkerOffset to be a function.

3. Uses a dummy struct to compute the size of a compressed
   pc descriptor to avoid alignment issues. sizeof(PcDescriptorRec)
   is 16 on ia32 and arm. Subtracting sizeof(int16_t) gives 14,
   which creates alignment problems on ARM, i.e. poor performance on
   ARMv6 and later, and wrong results on ARMv5 and earlier.

R=regis@google.com

Committed: https://code.google.com/p/dart/source/detail?r=39250

[regis, 2014-08-13 19:47:39]

LGTM

https://codereview.chromium.org/467103005/diff/1/runtime/vm/assembler_arm.cc
File runtime/vm/assembler_arm.cc (right):

https://codereview.chromium.org/467103005/diff/1/runtime/vm/assembler_arm.cc#...
runtime/vm/assembler_arm.cc:561: if (TargetCPUFeatures::arm_version() ==
ARMv5TE) {
Can you add a comment explaining why this is needed?

[zra, 2014-08-13 20:08:55]

https://codereview.chromium.org/467103005/diff/1/runtime/vm/assembler_arm.cc
File runtime/vm/assembler_arm.cc (right):

https://codereview.chromium.org/467103005/diff/1/runtime/vm/assembler_arm.cc#...
runtime/vm/assembler_arm.cc:561: if (TargetCPUFeatures::arm_version() ==
ARMv5TE) {
On 2014/08/13 19:47:39, regis wrote:
> Can you add a comment explaining why this is needed?

Done.

[zra, 2014-08-14 15:42:13]

Committed patchset #2 manually as r39250 (presubmit successful).