setup: add compiler flags when appropriate

Author: james-d-mitchell

setup.py

@@ -11,10 +11,17 @@
 
 import glob
 import os
+import platform
 import sys
 
 import pkgconfig
-from pybind11.setup_helpers import ParallelCompile, Pybind11Extension, build_ext, naive_recompile
+from pybind11.setup_helpers import (
+    ParallelCompile,
+    Pybind11Extension,
+    build_ext,
+    has_flag,
+    naive_recompile,
+)
 from setuptools import setup
 
 ParallelCompile("NPY_NUM_BUILD_JOBS", needs_recompile=naive_recompile).install()
@@ -41,6 +48,49 @@
 print("Library directories args are:")
 print(libsemigroups_info["library_dirs"])
 
+
+def get_arch():
+    """Simple function to return the architecture, namely, x86 or not"""
+    arch = platform.machine().lower()
+    if arch in {"x86_64", "amd64", "i386", "i686"}:
+        return "x86"
+    if arch in {"arm64", "aarch64", "armv7l", "armv6l"}:
+        return "arm"
+    return arch
+
+
+class LibsemigroupsBuildExt(build_ext):
+    # pylint: disable=too-few-public-methods
+    """Class conditionally add compile flags"""
+
+    def build_extensions(self):
+        """Adds compile flags before calling build_extensions in build_ext"""
+        compiler = self.compiler
+
+        if has_flag(compiler, "-mavx"):
+            print("Compiler supports '-mavx' flag, adding it to 'extra_compile_args'")
+            for ext in self.extensions:
+                ext.extra_compile_args += ["-mavx"]
+        else:
+            print("Compiler does not support '-mavx' flag, not adding it to 'extra_compile_args'")
+        if get_arch() == "arm" and (
+            any(x.startswith("gcc") for x in compiler.compiler)
+            or any(x.startswith("g++") for x in compiler.compiler_cxx)
+        ):
+            print(
+                "Compiler is gcc, and architecture is arm, adding '-fpermissive' to "
+                "'extra_compile_args'"
+            )
+            for ext in self.extensions:
+                ext.extra_compile_args += ["-fpermissive"]
+
+        for ext in self.extensions:
+            print(f"'extra_compile_args' for '{ext.name}' are:")
+            print(ext.extra_compile_args)
+
+        super().build_extensions()
+
+
 ext_modules = [
     Pybind11Extension(
         "_libsemigroups_pybind11",
@@ -49,8 +99,8 @@
         library_dirs=libsemigroups_info["library_dirs"],
         language="c++",
         libraries=["semigroups"],
-        extra_compile_args=["-fpermissive", "-flax-vector-conversions"],
+        extra_compile_args=["-flax-vector-conversions"],
     )
 ]
 
-setup(ext_modules=ext_modules, cmdclass={"build_ext": build_ext})
+setup(ext_modules=ext_modules, cmdclass={"build_ext": LibsemigroupsBuildExt})