AMREX_FLATTEN (AMReX-Codes#3840)

This could be used to force inline calls in a function.

Src/Base/AMReX_Extension.H

@@ -112,6 +112,9 @@
 #elif defined(__GNUC__)
 #define AMREX_FORCE_INLINE inline __attribute__((always_inline))
 
+#elif defined(_MSC_VER)
+#define AMREX_FORCE_INLINE inline __forceinline
+
 #else
 #define AMREX_FORCE_INLINE inline
 
@@ -133,6 +136,15 @@
 #define AMREX_NO_INLINE
 #endif
 
+// flatten
+#if defined(_MSC_VER)
+#define AMREX_FLATTEN [[msvc::flatten]]
+#elif defined(__clang__) || defined(__GNUC__)
+#define AMREX_FLATTEN __attribute__((flatten))
+#else
+#define AMREX_FLATTEN
+#endif
+
 // unroll loop
 #define AMREX_TO_STRING_HELPER(X)   #X
 #define AMREX_TO_STRING(X)          AMREX_TO_STRING_HELPER(X)