From b7e03028c2d7154782ba1ea3de9a28cfa06466b8 Mon Sep 17 00:00:00 2001
From: Kevin Ushey <kevinushey@gmail.com>
Date: Thu, 23 Jul 2026 15:48:05 -0700
Subject: [PATCH] apply cpuid guard to tbb headers copied at install time

On Windows, RcppParallel ships the TBB headers provided by Rtools, not
the bundled copy of oneTBB -- useTbbPreamble() copies them from TBB_INC
at build time. The __cpuid guard added in #248 patched only the bundled
sources, so installed packages on Windows never received it, and the
cpuid.h/intrin.h include-order conflict persisted.

Post-process the copied _machine.h in useTbbPreamble() instead, applying
the same guard to whichever headers are actually installed. The patch
function is idempotent and bails if the header does not have the
expected form.
---
 NEWS.md            |  3 ++-
 src/install.libs.R | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 4bcdac2f..661b4c50 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,7 +7,8 @@
   RcppParallel 6.0.0, such packages would fail to load with "LoadLibrary
   failure: The specified module could not be found".
 
-* The bundled oneTBB headers now guard against GCC's `<cpuid.h>` being
+* The TBB headers installed with RcppParallel (whether from Rtools or from
+  the bundled copy of oneTBB) now guard against GCC's `<cpuid.h>` being
   included before `<intrin.h>` on Windows (mingw). Previously, translation
   units including `<cpuid.h>` before any TBB header would fail to compile,
   as the `__cpuid` macro from `<cpuid.h>` conflicts with the `__cpuid()`
diff --git a/src/install.libs.R b/src/install.libs.R
index 142914c4..06a7899b 100644
--- a/src/install.libs.R
+++ b/src/install.libs.R
@@ -88,6 +88,7 @@
 }
 
 useTbbPreamble <- function(tbbInc) {
+
    dir.create("../inst/include", recursive = TRUE, showWarnings = FALSE)
    for (suffix in c("oneapi", "serial", "tbb")) {
       tbbPath <- file.path(tbbInc, suffix)
@@ -95,6 +96,45 @@ useTbbPreamble <- function(tbbInc) {
          file.copy(tbbPath, "../inst/include", recursive = TRUE)
       }
    }
+
+   patchTbbMachineHeader("../inst/include/oneapi/tbb/detail/_machine.h")
+
+}
+
+# Guard the '#include <intrin.h>' in TBB's _machine.h against GCC's
+# <cpuid.h> macro on mingw. The headers we ship may come from Rtools
+# rather than from the bundled copy of oneTBB, so the guard must be
+# applied to the copied headers, not just the bundled sources.
+patchTbbMachineHeader <- function(path) {
+
+   if (!file.exists(path))
+      return()
+
+   contents <- readLines(path)
+   if (any(grepl("push_macro", contents, fixed = TRUE)))
+      return()
+
+   index <- which(contents == "#include <intrin.h>")
+   if (length(index) != 1L)
+      return()
+
+   replacement <- c(
+      "// GCC's <cpuid.h> defines a function-like '__cpuid' macro that mangles the",
+      "// __cpuid() declarations in mingw's <intrin.h>. Hide the macro while",
+      "// including <intrin.h> so the two headers can coexist in any order.",
+      "#if defined(__MINGW32__) && defined(__cpuid)",
+      "#pragma push_macro(\"__cpuid\")",
+      "#undef __cpuid",
+      "#include <intrin.h>",
+      "#pragma pop_macro(\"__cpuid\")",
+      "#else",
+      "#include <intrin.h>",
+      "#endif"
+   )
+
+   contents <- append(contents[-index], replacement, after = index - 1L)
+   writeLines(contents, path)
+
 }
 
 useSystemTbb <- function(tbbLib, tbbInc) {