From e3c361b8cb335b13b45caa8a950d8ccbf4585679 Mon Sep 17 00:00:00 2001
From: Joshua Root <jmr@macports.org>
Date: Sun, 23 Aug 2020 11:33:15 +1000
Subject: [PATCH] bpo-41617: check for bswap builtins before using

Don't assume clang always has them; use __has_builtin to check.
---
 Include/internal/pycore_bitutils.h | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/Include/internal/pycore_bitutils.h b/Include/internal/pycore_bitutils.h
index 0bd3270fe82e5c..aa2a489f13c1f5 100644
--- a/Include/internal/pycore_bitutils.h
+++ b/Include/internal/pycore_bitutils.h
@@ -17,9 +17,14 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
-#if defined(__clang__) || \
-    (defined(__GNUC__) && \
-     ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8)))
+// Don't break compilers that don't know about __has_builtin
+#ifndef __has_builtin
+#  define __has_builtin(x) 0
+#endif
+
+// No check for clang here, __has_builtin is used instead
+#if defined(__GNUC__) && \
+     ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8))
    /* __builtin_bswap16() is available since GCC 4.8,
       __builtin_bswap32() is available since GCC 4.3,
       __builtin_bswap64() is available since GCC 4.3. */
@@ -34,7 +39,7 @@ extern "C" {
 static inline uint16_t
 _Py_bswap16(uint16_t word)
 {
-#ifdef _PY_HAVE_BUILTIN_BSWAP
+#if defined(_PY_HAVE_BUILTIN_BSWAP) || __has_builtin(__builtin_bswap16)
     return __builtin_bswap16(word);
 #elif defined(_MSC_VER)
     Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned short));
@@ -49,7 +54,7 @@ _Py_bswap16(uint16_t word)
 static inline uint32_t
 _Py_bswap32(uint32_t word)
 {
-#ifdef _PY_HAVE_BUILTIN_BSWAP
+#if defined(_PY_HAVE_BUILTIN_BSWAP) || __has_builtin(__builtin_bswap32)
     return __builtin_bswap32(word);
 #elif defined(_MSC_VER)
     Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned long));
@@ -66,7 +71,7 @@ _Py_bswap32(uint32_t word)
 static inline uint64_t
 _Py_bswap64(uint64_t word)
 {
-#ifdef _PY_HAVE_BUILTIN_BSWAP
+#if defined(_PY_HAVE_BUILTIN_BSWAP) || __has_builtin(__builtin_bswap64)
     return __builtin_bswap64(word);
 #elif defined(_MSC_VER)
     return _byteswap_uint64(word);