ARM: Make use of d16-d31 when available.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 338060f3fc0d3074252a18cc122903c0d99fae78..2a8a5d29604c5f3132c4048e0e0b01fd32fbcee9 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -298,6 +298,8 @@ DEFINE_bool(enable_movw_movt, false,
             "instruction pairs (ARM only)")
 DEFINE_bool(enable_unaligned_accesses, true,
             "enable unaligned accesses for ARMv7 (ARM only)")
+DEFINE_bool(enable_32dregs, false,

[Rodolph Perfetta, 2012/12/17 20:03:25]

I would set this to true by default and update CpuFeatures::IsSupported to be
overridden by the flag when it is false (in the same way as VFP3).

currently the flag only seems to affect the simulator:
 * on the command line if you set the flag to true but the hardware doesn't
support it, it will be ignored.
 * when the flag is false but the hardware provides 32 D-regs then the feature
is enabled by runtime probing.

If you default to true and update IsSupported then you can disabled the feature
even if the CPU supports it.

[hans, 2012/12/18 11:09:08]

I was worried that this would get included in the snapshot if enabled by
default, but after talking to Ulan we concluded that this doesn't happen because
CpuFeatures::Probe() returns early in the case that the serializer is enabled.

Also added a compile-time flag that can be used to enable this feature both for
the snapshot and target.

+            "enable use of d16-d31 registers on ARM - this requires VFP3")
 DEFINE_bool(enable_fpu, true,
             "enable use of MIPS FPU instructions if available (MIPS only)")