[ARM] ARMv6m and v8m.baseline strict align target feature

[SjoerdMeijer]

Summary

This sets target feature FeatureStrictAlign for both the Cortex-M0
and Cortex-M0+, because there is no support for unaligned accesses
on these Cortex-M0 processors.
It looks like we always pass target feature "+strict-align" from
clang, so this is not a user facing problem, but setting this
target feature looks more correct to me (unless I of course miss
something here).

[olista01]

This restriction is in the Armv6M architecture, so I think this should be done in ARMv6m, so it also applies to cortex-m1 and sc000, and I think this also applies to ARMv8mBaseline.

[SjoerdMeijer]

Ah, of course, thanks. And I will add some tests too.

[samparker]

This feature probably should be added as a subtarget of ARMv6m and I guess v8m.baseline too.

[samparker]

ah, good ol' refresh delay.

[SjoerdMeijer]

Added tests, i.e. removed the strict-align attribute from some tests where we also pass cpu=cortex-m0 and m1, so this checks that build attribute:

.eabi_attribute 34, 0

is still set.

[SjoerdMeijer]

Forgot v8m.baseline, adding this now.

[SjoerdMeijer]

Added v8m.baseline

[samparker]

LGTM.

lib/Target/ARM/ARM.td

 def : ProcNoItin<"xscale",                              [ARMv5te]>;
 def : ProcNoItin<"iwmmxt",                              [ARMv5te]>;
 
 def : Processor<"arm1136j-s",       ARMV6Itineraries,   [ARMv6]>;
 def : Processor<"arm1136jf-s",      ARMV6Itineraries,   [ARMv6,
                                                          FeatureVFP2,
                                                          FeatureHasSlowFPVMLx]>;
 
-def : Processor<"cortex-m0",        ARMV6Itineraries,   [ARMv6m]>;
-def : Processor<"cortex-m0plus",    ARMV6Itineraries,   [ARMv6m]>;
+def : Processor<"cortex-m0",        ARMV6Itineraries,   [ARMv6m,
+                                                         FeatureStrictAlign]>;
+def : Processor<"cortex-m0plus",    ARMV6Itineraries,   [ARMv6m,
+                                                         FeatureStrictAlign]>;
 def : Processor<"cortex-m1",        ARMV6Itineraries,   [ARMv6m]>;
 def : Processor<"sc000",            ARMV6Itineraries,   [ARMv6m]>;
 
 def : Processor<"arm1176j-s",       ARMV6Itineraries,   [ARMv6kz]>;
 def : Processor<"arm1176jz-s",      ARMV6Itineraries,   [ARMv6kz]>;
 def : Processor<"arm1176jzf-s",     ARMV6Itineraries,   [ARMv6kz,
                                                          FeatureVFP2,
                                                          FeatureHasSlowFPVMLx]>;