[ARM][AArch64] generate subtarget feature flags

This patch aims to reduce a lot of the boilerplate around adding new subtarget
features. From the SubtargetFeatures tablegen definitions, a series of calls to
the macro GET_SUBTARGETINFO_MACRO are generated in
ARM/AArch64GenSubtargetInfo.inc.  ARMSubtarget/AArch64Subtarget can then use
this macro to define bool members and the corresponding getter methods.

Some naming inconsistencies have been fixed to allow this, and one unused
member removed.

This implementation only applies to boolean members; in future both BitVector
and enum members could also be generated.

Differential Revision: https://reviews.llvm.org/D120906

Author: tmatheson-arm

llvm/lib/Target/AArch64/AArch64.td

@@ -154,6 +154,10 @@ def FeatureZCRegMove : SubtargetFeature<"zcm", "HasZeroCycleRegMove", "true",
 def FeatureZCZeroingGP : SubtargetFeature<"zcz-gp", "HasZeroCycleZeroingGP", "true",
                                         "Has zero-cycle zeroing instructions for generic registers">;
 
+// It is generally beneficial to rewrite "fmov s0, wzr" to "movi d0, #0".
+// as movi is more efficient across all cores. Newer cores can eliminate
+// fmovs early and there is no difference with movi, but this not true for
+// all implementations.
 def FeatureNoZCZeroingFP : SubtargetFeature<"no-zcz-fp", "HasZeroCycleZeroingFP", "false",
                                         "Has no zero-cycle zeroing instructions for FP registers">;
 
@@ -168,7 +172,7 @@ def FeatureZCZeroingFPWorkaround : SubtargetFeature<"zcz-fp-workaround",
     "The zero-cycle floating-point zeroing instruction has a bug">;
 
 def FeatureStrictAlign : SubtargetFeature<"strict-align",
-                                          "StrictAlign", "true",
+                                          "RequiresStrictAlign", "true",
                                           "Disallow all unaligned memory "
                                           "access">;
 
@@ -190,24 +194,24 @@ def FeaturePredictableSelectIsExpensive : SubtargetFeature<
     "Prefer likely predicted branches over selects">;
 
 def FeatureCustomCheapAsMoveHandling : SubtargetFeature<"custom-cheap-as-move",
-    "CustomAsCheapAsMove", "true",
+    "HasCustomCheapAsMoveHandling", "true",
     "Use custom handling of cheap instructions">;
 
 def FeatureExynosCheapAsMoveHandling : SubtargetFeature<"exynos-cheap-as-move",
-    "ExynosAsCheapAsMove", "true",
+    "HasExynosCheapAsMoveHandling", "true",
     "Use Exynos specific handling of cheap instructions",
     [FeatureCustomCheapAsMoveHandling]>;
 
 def FeaturePostRAScheduler : SubtargetFeature<"use-postra-scheduler",
     "UsePostRAScheduler", "true", "Schedule again after register allocation">;
 
 def FeatureSlowMisaligned128Store : SubtargetFeature<"slow-misaligned-128store",
-    "Misaligned128StoreIsSlow", "true", "Misaligned 128 bit stores are slow">;
+    "IsMisaligned128StoreSlow", "true", "Misaligned 128 bit stores are slow">;
 
 def FeatureSlowPaired128 : SubtargetFeature<"slow-paired-128",
-    "Paired128IsSlow", "true", "Paired 128 bit loads and stores are slow">;
+    "IsPaired128Slow", "true", "Paired 128 bit loads and stores are slow">;
 
-def FeatureSlowSTRQro : SubtargetFeature<"slow-strqro-store", "STRQroIsSlow",
+def FeatureSlowSTRQro : SubtargetFeature<"slow-strqro-store", "IsSTRQroSlow",
     "true", "STR of Q register with register offset is slow">;
 
 def FeatureAlternateSExtLoadCVTF32Pattern : SubtargetFeature<