Remove XSIMD_IF_CONSTEXPR macros, use if constexpr instead (#1382)

* Remove XSIMD_IF_CONSTEXPR macros, use if constexpr instead

* Remove XIMSD_NO_DISCARD, use [[nodiscard]] instead

* Fixed linter

Author: JohanMabille

docs/Doxyfile

@@ -46,6 +46,5 @@ WARN_AS_ERROR = NO
 ENABLE_PREPROCESSING = YES
 MACRO_EXPANSION      = YES
 EXPAND_ONLY_PREDEF   = YES
-PREDEFINED           = XSIMD_NO_DISCARD= \
-                       XSIMD_INLINE=inline \
+PREDEFINED           = XSIMD_INLINE=inline \
                        DOXYGEN_SHOULD_SKIP_THIS=

docs/source/vectorized_code.rst

@@ -106,7 +106,7 @@ One that is simple and compiles on all platforms is using C++17 ``if constexpr``
         xsimd::batch<int8_t, Arch> const& y
     ) -> xsimd::batch<uint8_t, Arch> {
          // Dedicated instruction dispatch at compile time
-         if constexpr(std::is_same_v<Arch, xsimd::avx2>){
+         if constexpr (std::is_same_v<Arch, xsimd::avx2>){
              // Automatic conversion back and forth between xsimd::batch and native types
              return _mm256_sign_epi8(x, y);
              // When compiler complains we can be more explicit

include/xsimd/arch/common/xsimd_common_bit.hpp

@@ -57,7 +57,7 @@ namespace xsimd
 #if XSIMD_HAS_BUILTIN(__builtin_popcountg)
             return __builtin_popcountg(x);
 #else
-            XSIMD_IF_CONSTEXPR(sizeof(T) == 1)
+            if constexpr (sizeof(T) == 1)
             {
 #if XSIMD_HAS_BUILTIN(__builtin_popcount)
                 return __builtin_popcount(x);
@@ -68,7 +68,7 @@ namespace xsimd
                 return ((uint64_t)x * 0x200040008001ULL & 0x111111111111111ULL) % 0xf;
 #endif
             }
-            else XSIMD_IF_CONSTEXPR(sizeof(T) == 2)
+            else if constexpr (sizeof(T) == 2)
             {
 #if XSIMD_HAS_BUILTIN(__builtin_popcount)
                 return __builtin_popcount(x);
@@ -85,7 +85,7 @@ namespace xsimd
                     + (((v & 0xfff000) >> 12) * msb12 & mask5) % 0x1f;
 #endif
             }
-            else XSIMD_IF_CONSTEXPR(sizeof(T) == 4)
+            else if constexpr (sizeof(T) == 4)
             {
 #if XSIMD_HAS_BUILTIN(__builtin_popcount)
                 return __builtin_popcount(x);
@@ -132,7 +132,7 @@ namespace xsimd
             if (x == 0)
                 return sizeof(T) * CHAR_BIT;
 
-            XSIMD_IF_CONSTEXPR(sizeof(T) <= 4)
+            if constexpr (sizeof(T) <= 4)
             {
 #if XSIMD_HAS_BUILTIN(__builtin_clz)
                 return __builtin_clz((unsigned int)x) - (4 - sizeof(T)) * CHAR_BIT;
@@ -144,11 +144,11 @@ namespace xsimd
                 x |= x >> 1;
                 x |= x >> 2;
                 x |= x >> 4;
-                XSIMD_IF_CONSTEXPR(sizeof(T) >= 2)
+                if constexpr (sizeof(T) >= 2)
                 {
                     x |= x >> 8;
                 }
-                XSIMD_IF_CONSTEXPR(sizeof(T) >= 4)
+                if constexpr (sizeof(T) >= 4)
                 {
                     x |= x >> 16;
                 }
@@ -192,7 +192,7 @@ namespace xsimd
             if (x == 0)
                 return sizeof(T) * CHAR_BIT;
 
-            XSIMD_IF_CONSTEXPR(sizeof(T) <= 4)
+            if constexpr (sizeof(T) <= 4)
             {
 #if XSIMD_HAS_BUILTIN(__builtin_ctz)
                 return __builtin_ctz((unsigned int)x);

include/xsimd/arch/common/xsimd_common_memory.hpp

@@ -655,27 +655,27 @@ namespace xsimd
             static_assert(bsize == batch<T, A>::size, "valid shuffle");
 
             // Detect common patterns
-            XSIMD_IF_CONSTEXPR(detail::is_swizzle_fst(bsize, Indices...))
+            if constexpr (detail::is_swizzle_fst(bsize, Indices...))
             {
                 return swizzle(x, batch_constant<ITy, A, ((Indices >= bsize) ? 0 /* never happens */ : Indices)...>());
             }
 
-            XSIMD_IF_CONSTEXPR(detail::is_swizzle_snd(bsize, Indices...))
+            if constexpr (detail::is_swizzle_snd(bsize, Indices...))
             {
                 return swizzle(y, batch_constant<ITy, A, ((Indices >= bsize) ? (Indices - bsize) : 0 /* never happens */)...>());
             }
 
-            XSIMD_IF_CONSTEXPR(detail::is_zip_lo(bsize, Indices...))
+            if constexpr (detail::is_zip_lo(bsize, Indices...))
             {
                 return zip_lo(x, y);
             }
 
-            XSIMD_IF_CONSTEXPR(detail::is_zip_hi(bsize, Indices...))
+            if constexpr (detail::is_zip_hi(bsize, Indices...))
             {
                 return zip_hi(x, y);
             }
 
-            XSIMD_IF_CONSTEXPR(detail::is_select(bsize, Indices...))
+            if constexpr (detail::is_select(bsize, Indices...))
             {
                 return select(batch_bool_constant<T, A, (Indices < bsize)...>(), x, y);
             }