support aarch64 on Windows

Adapted from a patch shared by Tomas Kalibera.

R/tbb.R

@@ -81,6 +81,10 @@ tbbLdFlags <- function() {
       return(sprintf(fmt, asBuildPath(tbbLib)))
    }
 
+   # on Aarch64 builds, use the version of TBB provided by Rtools
+   if (is_windows() && R.version$arch == "aarch64")
+      return("-ltbb12 -ltbbmalloc")
+
    # on Mac, Windows and Solaris, we need to explicitly link (#206)
    needsExplicitFlags <- is_mac() || is_windows() || (is_solaris() && !is_sparc())
    if (needsExplicitFlags) {

R/zzz.R

@@ -27,8 +27,12 @@ loadTbbLibrary <- function(name) {
 
 .onLoad <- function(libname, pkgname) {
 
+   tbbLibraryName <- "tbb"
+   if (is_windows() && R.version$arch == "aarch64")
+      tbbLibraryName <- "tbb12"
+
    # load tbb, tbbmalloc
-   .tbbDllInfo       <<- loadTbbLibrary("tbb")
+   .tbbDllInfo       <<- loadTbbLibrary(tbbLibraryName)
    .tbbMallocDllInfo <<- loadTbbLibrary("tbbmalloc")
 
    # load tbbmalloc_proxy, but only if requested

src/Makevars.in

@@ -88,6 +88,14 @@ ifeq ($(USE_TBB), Windows)
 	# Linker needs access to the tbb dll; otherwise you get errors such as:
 	# "undefined reference to `tbb::task_scheduler_init::terminate()'"
 	PKG_LIBS += -Ltbb/build/lib_release -ltbb -ltbbmalloc
+
+	# override for aarch64 (experimental) to use Rtools TBB
+	ARCH=$(shell "${R_HOME}/bin/R" --vanilla -s -e 'cat(R.version$$arch)')
+	ifeq "$(ARCH)" "aarch64"
+		TBB_LIB = ${R_TOOLS_SOFT}
+		TBB_INC = ${R_TOOLS_SOFT}
+		PKG_LIBS = -ltbb12 -ltbbmalloc
+	endif
 
 endif