From 83bd3972d2e7e936fbee034105df91b453b24a25 Mon Sep 17 00:00:00 2001
From: Leonidas Zhak <70497898+LeonidasZhak@users.noreply.github.com>
Date: Sat, 22 Aug 2026 03:44:59 +0800
Subject: [PATCH] Fix old macOS Clang allocation flags

---
 NEWS.md                  |  4 ++++
 R/tbb-autodetected.R.in  |  3 ++-
 R/tbb-platform.R         | 34 ++++++++++++++++++++++++++++++++++
 R/tbb.R                  |  3 +++
 src/Makevars.in          |  3 ++-
 tests/test-cxx-flags.R   | 18 ++++++++++++++++++
 tools/config/configure.R | 11 ++++++++++-
 7 files changed, 73 insertions(+), 3 deletions(-)
 create mode 100644 R/tbb-platform.R
 create mode 100644 tests/test-cxx-flags.R

diff --git a/NEWS.md b/NEWS.md
index bc5515ae..05579225 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,9 @@
 # RcppParallel (development version)
 
+* Fixed bundled oneTBB builds and downstream compilation on macOS 10.12 and
+  earlier with Clang and libc++, which require `-fno-aligned-allocation`.
+  The flag is restricted to that compiler and platform combination. (#219)
+
 
 # RcppParallel 6.2.0
 
diff --git a/R/tbb-autodetected.R.in b/R/tbb-autodetected.R.in
index 7cc750e0..0be09b76 100644
--- a/R/tbb-autodetected.R.in
+++ b/R/tbb-autodetected.R.in
@@ -2,6 +2,7 @@
 TBB_ENABLED <- @TBB_ENABLED@
 TBB_LIB  <- "@TBB_LIB@"
 TBB_INC  <- "@TBB_INC@"
+TBB_CXXFLAGS <- "@TBB_CXXFLAGS@"
 
 TBB_NAME <- "@TBB_NAME@"
-TBB_MALLOC_NAME <- "@TBB_MALLOC_NAME@"
\ No newline at end of file
+TBB_MALLOC_NAME <- "@TBB_MALLOC_NAME@"
diff --git a/R/tbb-platform.R b/R/tbb-platform.R
new file mode 100644
index 00000000..26eea3bd
--- /dev/null
+++ b/R/tbb-platform.R
@@ -0,0 +1,34 @@
+tbb_cxx_compiler <- function() {
+
+   compiler <- Sys.getenv("CXX", unset = NA_character_)
+   if (!is.na(compiler) && nzchar(compiler))
+      return(compiler)
+
+   R <- file.path(R.home("bin"), "R")
+   output <- tryCatch(
+      system2(R, c("CMD", "config", "CXX"), stdout = TRUE, stderr = FALSE),
+      error = function(cnd) character()
+   )
+
+   if (length(output)) output[[1L]] else ""
+
+}
+
+tbb_needs_no_aligned_allocation <- function(
+   sysname = Sys.info()[["sysname"]],
+   release = Sys.info()[["release"]],
+   compiler = tbb_cxx_compiler())
+{
+
+   if (!identical(sysname, "Darwin"))
+      return(FALSE)
+
+   # Darwin 16 is macOS 10.12; Darwin 17 is macOS 10.13.
+   darwinMajor <- suppressWarnings(as.integer(strsplit(release, ".", fixed = TRUE)[[1L]][[1L]]))
+   if (is.na(darwinMajor) || darwinMajor >= 17L)
+      return(FALSE)
+
+   compiler <- strsplit(compiler, "[[:space:]]+", perl = TRUE)[[1L]][[1L]]
+   identical(basename(compiler), "clang++")
+
+}
diff --git a/R/tbb.R b/R/tbb.R
index 6f6a745c..b071833a 100644
--- a/R/tbb.R
+++ b/R/tbb.R
@@ -57,6 +57,9 @@ tbbCxxFlags <- function() {
    
    flags <- c("-DRCPP_PARALLEL_USE_TBB=1")
 
+   if (nzchar(TBB_CXXFLAGS))
+      flags <- c(flags, TBB_CXXFLAGS)
+
    # if TBB_INC is set, apply those library paths
    tbbInc <- Sys.getenv("TBB_INC", unset = TBB_INC)
    if (!file.exists(tbbInc)) {
diff --git a/src/Makevars.in b/src/Makevars.in
index 7158b732..06416fce 100644
--- a/src/Makevars.in
+++ b/src/Makevars.in
@@ -10,6 +10,7 @@ TBB_LIB         = @TBB_LIB@
 TBB_INC         = @TBB_INC@
 TBB_NAME        = @TBB_NAME@
 TBB_MALLOC_NAME = @TBB_MALLOC_NAME@
+TBB_CXXFLAGS    = @TBB_CXXFLAGS@
 
 PKG_CPPFLAGS = @PKG_CPPFLAGS@
 PKG_CXXFLAGS = @PKG_CXXFLAGS@
@@ -28,7 +29,7 @@ tbb: tbb-clean
 	@TBB_LIB="$(TBB_LIB)" TBB_INC="$(TBB_INC)"                  \
 	TBB_NAME="$(TBB_NAME)" TBB_MALLOC_NAME="$(TBB_MALLOC_NAME)" \
 	CC="$(CC)" CFLAGS="$(CFLAGS)" CPPFLAGS="$(CPPFLAGS)"        \
-	CXX="$(CXX)" CXXFLAGS="$(CXXFLAGS)"	LDFLAGS="$(LDFLAGS)"    \
+	CXX="$(CXX)" CXXFLAGS="$(CXXFLAGS) $(TBB_CXXFLAGS)"	LDFLAGS="$(LDFLAGS)"    \
 	CMAKE="$(CMAKE)" "@R@" -s -f install.libs.R --args build
 
 # NOTE: we do not want to clean ../inst/lib or ../inst/libs here,
diff --git a/tests/test-cxx-flags.R b/tests/test-cxx-flags.R
new file mode 100644
index 00000000..61ca76f2
--- /dev/null
+++ b/tests/test-cxx-flags.R
@@ -0,0 +1,18 @@
+# Unit tests for the compiler and platform-specific flags returned by
+# RcppParallel::CxxFlags().
+
+RcppParallel:::test_init()
+
+# Darwin 16 is macOS 10.12, the last release affected by this libc++ issue.
+assert(tbb_needs_no_aligned_allocation("Darwin", "16.7.0", "clang++"))
+assert(!tbb_needs_no_aligned_allocation("Darwin", "17.0.0", "clang++"))
+assert(!tbb_needs_no_aligned_allocation("Darwin", "16.7.0", "g++"))
+assert(!tbb_needs_no_aligned_allocation("Linux", "16.7.0", "clang++"))
+
+flags <- tbbCxxFlags()
+assert(is.character(flags))
+assert(length(flags) == 1L)
+assert(!is.na(flags))
+
+if (nzchar(TBB_CXXFLAGS))
+   assert(grepl("-fno-aligned-allocation", flags, fixed = TRUE))
diff --git a/tools/config/configure.R b/tools/config/configure.R
index 6293fe13..290d21fe 100644
--- a/tools/config/configure.R
+++ b/tools/config/configure.R
@@ -3,6 +3,8 @@
 rExe <- if (.Platform$OS.type == "windows") "R.exe" else "R"
 define(R = file.path(R.home("bin"), rExe))
 
+source("R/tbb-platform.R")
+
 # check whether user has Makevars file that might cause trouble
 makevars <- Sys.getenv("R_MAKEVARS_USER", unset = "~/.R/Makevars")
 if (file.exists(makevars)) {
@@ -237,7 +239,14 @@ if (!is.na(tbbLib)) {
 # TBB is always enabled: either one was supplied via TBB_LIB / TBB_ROOT, or we
 # built the bundled copy, and failing to do either is fatal above
 define(TBB_ENABLED = TRUE)
-define(PKG_CXXFLAGS = "-DRCPP_PARALLEL_USE_TBB=1")
+tbbCxxFlags <- if (tbb_needs_no_aligned_allocation()) {
+   "-fno-aligned-allocation"
+} else {
+   ""
+}
+define(TBB_CXXFLAGS = tbbCxxFlags)
+pkgCxxFlags <- c("-DRCPP_PARALLEL_USE_TBB=1", tbbCxxFlags)
+define(PKG_CXXFLAGS = paste(pkgCxxFlags[nzchar(pkgCxxFlags)], collapse = " "))
 
 # macOS needs some extra flags set
 if (Sys.info()[["sysname"]] == "Darwin") {