[PATCH] D131826: [MC] Leverage constexpr `std::array` in `SubtargetFeature.h`

[Joe Loser via Phabricator via llvm-commits]

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Replace C-style array with `std::array` since `std::array<T, N>::operator[]` is
`constexpr` in C++17. This also allows us to replace `array_lengthof` calls with
member `size()` function.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131826

Files:
  llvm/include/llvm/MC/SubtargetFeature.h


Index: llvm/include/llvm/MC/SubtargetFeature.h
===================================================================
--- llvm/include/llvm/MC/SubtargetFeature.h
+++ llvm/include/llvm/MC/SubtargetFeature.h
@@ -40,14 +40,11 @@
 class FeatureBitset {
   static_assert((MAX_SUBTARGET_FEATURES % 64) == 0,
                 "Should be a multiple of 64!");
-  // This cannot be a std::array, operator[] is not constexpr until C++17.
-  uint64_t Bits[MAX_SUBTARGET_WORDS] = {};
+  std::array<uint64_t, MAX_SUBTARGET_WORDS> Bits{};
 
 protected:
-  constexpr FeatureBitset(const std::array<uint64_t, MAX_SUBTARGET_WORDS> &B) {
-    for (unsigned I = 0; I != B.size(); ++I)
-      Bits[I] = B[I];
-  }
+  constexpr FeatureBitset(const std::array<uint64_t, MAX_SUBTARGET_WORDS> &B)
+      : Bits{b} {}
 
 public:
   constexpr FeatureBitset() = default;
@@ -103,7 +100,7 @@
   }
 
   constexpr FeatureBitset &operator^=(const FeatureBitset &RHS) {
-    for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+    for (unsigned I = 0, E = Bits.size(); I != E; ++I) {
       Bits[I] ^= RHS.Bits[I];
     }
     return *this;
@@ -115,7 +112,7 @@
   }
 
   constexpr FeatureBitset &operator&=(const FeatureBitset &RHS) {
-    for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+    for (unsigned I = 0, E = Bits.size(); I != E; ++I) {
       Bits[I] &= RHS.Bits[I];
     }
     return *this;
@@ -127,7 +124,7 @@
   }
 
   constexpr FeatureBitset &operator|=(const FeatureBitset &RHS) {
-    for (unsigned I = 0, E = array_lengthof(Bits); I != E; ++I) {
+    for (unsigned I = 0, E = Bits.size(); I != E; ++I) {
       Bits[I] |= RHS.Bits[I];
     }
     return *this;


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