python · JukkaL · Nov 28, 2025 · Nov 18, 2025 · Nov 27, 2025 · Nov 27, 2025
diff --git a/mypy_self_check.ini b/mypy_self_check.ini
@@ -8,7 +8,7 @@ pretty = True
 always_false = MYPYC
 plugins = mypy.plugins.proper_plugin
 python_version = 3.9
-exclude = mypy/typeshed/|mypyc/test-data/|mypyc/lib-rt/
+exclude = mypy/typeshed/|mypyc/test-data/
 enable_error_code = ignore-without-code,redundant-expr
 enable_incomplete_feature = PreciseTupleTypes
 show_error_code_links = True

diff --git a/mypyc/build.py b/mypyc/build.py
@@ -28,6 +28,7 @@
 from collections.abc import Iterable
 from typing import TYPE_CHECKING, Any, NamedTuple, NoReturn, Union, cast
 
+import mypyc.build_setup  # noqa: F401
 from mypy.build import BuildSource
 from mypy.errors import CompileError
 from mypy.fscache import FileSystemCache
@@ -36,7 +37,7 @@
 from mypy.util import write_junit_xml
 from mypyc.annotate import generate_annotated_html
 from mypyc.codegen import emitmodule
-from mypyc.common import IS_FREE_THREADED, RUNTIME_C_FILES, X86_64, shared_lib_name
+from mypyc.common import IS_FREE_THREADED, RUNTIME_C_FILES, shared_lib_name
 from mypyc.errors import Errors
 from mypyc.ir.pprint import format_modules
 from mypyc.namegen import exported_name
@@ -70,6 +71,13 @@ class ModDesc(NamedTuple):
             "base64/arch/neon64/codec.c",
         ],
         [
+            "base64/arch/avx/enc_loop_asm.c",
+            "base64/arch/avx2/enc_loop.c",
+            "base64/arch/avx2/enc_loop_asm.c",
+            "base64/arch/avx2/enc_reshuffle.c",
+            "base64/arch/avx2/enc_translate.c",
+            "base64/arch/avx2/dec_loop.c",
+            "base64/arch/avx2/dec_reshuffle.c",
             "base64/arch/generic/32/enc_loop.c",
             "base64/arch/generic/64/enc_loop.c",
             "base64/arch/generic/32/dec_loop.c",
@@ -661,9 +669,6 @@ def mypycify(
             # See https://github.com/mypyc/mypyc/issues/956
             "-Wno-cpp",
         ]
-        if X86_64:
-            # Enable SIMD extensions. All CPUs released since ~2010 support SSE4.2.
-            cflags.append("-msse4.2")
         if log_trace:
             cflags.append("-DMYPYC_LOG_TRACE")
         if experimental_features:
@@ -692,10 +697,6 @@ def mypycify(
             # that we actually get the compilation speed and memory
             # use wins that multi-file mode is intended for.
             cflags += ["/GL-", "/wd9025"]  # warning about overriding /GL
-        if X86_64:
-            # Enable SIMD extensions. All CPUs released since ~2010 support SSE4.2.
-            # Also Windows 11 requires SSE4.2 since 24H2.
-            cflags.append("/arch:SSE4.2")
         if log_trace:
             cflags.append("/DMYPYC_LOG_TRACE")
         if experimental_features:

diff --git a/mypyc/build_setup.py b/mypyc/build_setup.py
@@ -0,0 +1,63 @@
+import platform
+import sys
+
+try:
+    # Import setuptools so that it monkey-patch overrides distutils
+    import setuptools  # noqa: F401
+except ImportError:
+    pass
+
+if sys.version_info >= (3, 12):
+    # From setuptools' monkeypatch
+    from distutils import ccompiler  # type: ignore[import-not-found]
+else:
+    from distutils import ccompiler
+
+EXTRA_FLAGS_PER_COMPILER_TYPE_PER_PATH_COMPONENT = {
+    "unix": {
+        "base64/arch/ssse3": ["-mssse3", "-DBASE64_WITH_SSSE3"],
+        "base64/arch/sse41": ["-msse4.1", "-DBASE64_WITH_SSE41"],
+        "base64/arch/sse42": ["-msse4.2", "-DBASE64_WITH_SSE42"],
+        "base64/arch/avx2": ["-mavx2", "-DBASE64_WITH_AVX2"],
+        "base64/arch/avx": ["-mavx", "-DBASE64_WITH_AVX"],
 if compiler.compiler_type == "unix":  # type: ignore[attr-defined] 
     cflags += ["-O3"] 
 opt_level: str = "3", 
 if compiler.compiler_type == "unix":  # type: ignore[attr-defined] 
     cflags += ["-O3"] 
 opt_level: str = "3", 
 opt_level = int(os.environ.get("MYPYC_OPT_LEVEL", 0)) 
 if compiler.compiler_type == "unix":  # type: ignore[attr-defined] 
     cflags += ["-O3"] 
 opt_level: str = "3", 
 if compiler.compiler_type == "unix":  # type: ignore[attr-defined] 
     cflags += ["-O3"] 
 opt_level: str = "3", 
 opt_level = int(os.environ.get("MYPYC_OPT_LEVEL", 0)) 
+    },
+    "msvc": {
+        "base64/arch/sse42": ["/arch:SSE4.2", "/DBASE64_WITH_SSE42"],
+        "base64/arch/avx2": ["/arch:AVX2", "/DBASE64_WITH_AVX2"],
+        "base64/arch/avx": ["/arch:AVX", "/DBASE64_WITH_AVX"],
+    },
+}
+
+ccompiler.CCompiler.__spawn = ccompiler.CCompiler.spawn  # type: ignore[attr-defined]
+X86_64 = platform.machine() in ("x86_64", "AMD64", "amd64")
+
+
+def spawn(self, cmd, **kwargs) -> None:  # type: ignore[no-untyped-def]
+    compiler_type: str = self.compiler_type
+    extra_options = EXTRA_FLAGS_PER_COMPILER_TYPE_PER_PATH_COMPONENT[compiler_type]
+    new_cmd = list(cmd)
+    if X86_64 and extra_options is not None:
+        # filenames are closer to the end of command line
+        for argument in reversed(new_cmd):
+            # Check if argument contains a filename. We must check for all
+            # possible extensions; checking for target extension is faster.
+            if self.obj_extension and not str(argument).endswith(self.obj_extension):
+                continue
+
+            for path in extra_options.keys():
+                if path in str(argument):
+                    if compiler_type == "bcpp":
+                        compiler = new_cmd.pop()
+                        # Borland accepts a source file name at the end,
+                        # insert the options before it
+                        new_cmd.extend(extra_options[path])
+                        new_cmd.append(compiler)
+                    else:
+                        new_cmd.extend(extra_options[path])
+
+                    # path component is found, no need to search any further
+                    break
+    self.__spawn(new_cmd, **kwargs)
+
+
+ccompiler.CCompiler.spawn = spawn  # type: ignore[method-assign]
diff --git a/mypyc/common.py b/mypyc/common.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import platform
 import sys
 import sysconfig
 from typing import Any, Final
@@ -45,8 +44,6 @@
 
 IS_32_BIT_PLATFORM: Final = int(SIZEOF_SIZE_T) == 4
 
-X86_64: Final = platform.machine() in ("x86_64", "AMD64", "amd64")
-
 PLATFORM_SIZE = 4 if IS_32_BIT_PLATFORM else 8
 
 # Maximum value for a short tagged integer.

diff --git a/mypyc/lib-rt/base64/arch/avx/codec.c b/mypyc/lib-rt/base64/arch/avx/codec.c
@@ -24,7 +24,7 @@
 #include "../ssse3/dec_loop.c"
 
 #if BASE64_AVX_USE_ASM
-# include "enc_loop_asm.c"
+# include "./enc_loop_asm.c"
 #else
 # include "../ssse3/enc_translate.c"
 # include "../ssse3/enc_reshuffle.c"

diff --git a/mypyc/lib-rt/base64/arch/avx2/codec.c b/mypyc/lib-rt/base64/arch/avx2/codec.c
@@ -20,15 +20,15 @@
 # endif
 #endif
 
-#include "dec_reshuffle.c"
-#include "dec_loop.c"
+#include "./dec_reshuffle.c"
+#include "./dec_loop.c"
 
 #if BASE64_AVX2_USE_ASM
-# include "enc_loop_asm.c"
+# include "./enc_loop_asm.c"
 #else
-# include "enc_translate.c"
-# include "enc_reshuffle.c"
-# include "enc_loop.c"
+# include "./enc_translate.c"
+# include "./enc_reshuffle.c"
+# include "./enc_loop.c"
 #endif
 
 #endif	// HAVE_AVX2

diff --git a/mypyc/lib-rt/base64/config.h b/mypyc/lib-rt/base64/config.h
@@ -1,27 +1,16 @@
 #ifndef BASE64_CONFIG_H
 #define BASE64_CONFIG_H
 
-#define BASE64_WITH_SSSE3 0
 #define HAVE_SSSE3 BASE64_WITH_SSSE3
 
-#define BASE64_WITH_SSE41 0
 #define HAVE_SSE41 BASE64_WITH_SSE41
 
-#if defined(__x86_64__) || defined(_M_X64)
-#define BASE64_WITH_SSE42 1
-#else
-#define BASE64_WITH_SSE42 0
-#endif
-
 #define HAVE_SSE42 BASE64_WITH_SSE42
 
-#define BASE64_WITH_AVX 0
 #define HAVE_AVX BASE64_WITH_AVX
 
-#define BASE64_WITH_AVX2 0
 #define HAVE_AVX2 BASE64_WITH_AVX2
 
-#define BASE64_WITH_AVX512 0
 #define HAVE_AVX512 BASE64_WITH_AVX512
 
 #define BASE64_WITH_NEON32 0

diff --git a/mypyc/lib-rt/setup.py b/mypyc/lib-rt/setup.py
@@ -25,9 +25,56 @@
     "pythonsupport.c",
 ]
 
+EXTRA_FLAGS_PER_COMPILER_TYPE_PER_PATH_COMPONENT = {
+    "unix": {
+        "base64/arch/ssse3": ["-mssse3", "-DBASE64_WITH_SSSE3"],
+        "base64/arch/sse41": ["-msse4.1", "-DBASE64_WITH_SSE41"],
+        "base64/arch/sse42": ["-msse4.2", "-DBASE64_WITH_SSE42"],
+        "base64/arch/avx2": ["-mavx2", "-DBASE64_WITH_AVX2"],
+        "base64/arch/avx": ["-mavx", "-DBASE64_WITH_AVX"],
+    },
+    "msvc": {
+        "base64/arch/sse42": ["/arch:SSE4.2", "/DBASE64_WITH_SSE42"],
+        "base64/arch/avx2": ["/arch:AVX2", "/DBASE64_WITH_AVX2"],
+        "base64/arch/avx": ["/arch:AVX", "/DBASE64_WITH_AVX"],
+    },
+}
+
+ccompiler.CCompiler.__spawn = ccompiler.CCompiler.spawn  # type: ignore[attr-defined]
 X86_64 = platform.machine() in ("x86_64", "AMD64", "amd64")
 
 
+def spawn(self, cmd, **kwargs) -> None:  # type: ignore[no-untyped-def]
+    compiler_type: str = self.compiler_type
+    extra_options = EXTRA_FLAGS_PER_COMPILER_TYPE_PER_PATH_COMPONENT[compiler_type]
+    new_cmd = list(cmd)
+    if X86_64 and extra_options is not None:
+        # filenames are closer to the end of command line
+        for argument in reversed(new_cmd):
+            # Check if argument contains a filename. We must check for all
+            # possible extensions; checking for target extension is faster.
+            if self.obj_extension and not str(argument).endswith(self.obj_extension):
+                continue
+
+            for path in extra_options.keys():
+                if path in str(argument):
+                    if compiler_type == "bcpp":
+                        compiler = new_cmd.pop()
+                        # Borland accepts a source file name at the end,
+                        # insert the options before it
+                        new_cmd.extend(extra_options[path])
+                        new_cmd.append(compiler)
+                    else:
+                        new_cmd.extend(extra_options[path])
+
+                    # path component is found, no need to search any further
+                    break
+    self.__spawn(new_cmd, **kwargs)
+
+
+ccompiler.CCompiler.spawn = spawn  # type: ignore[method-assign]
+
+
 class BuildExtGtest(build_ext):
     def get_library_names(self) -> list[str]:
         return ["gtest"]
@@ -80,14 +127,10 @@ def run(self) -> None:
     compiler = ccompiler.new_compiler()
     sysconfig.customize_compiler(compiler)
     cflags: list[str] = []
-    if compiler.compiler_type == "unix":
+    if compiler.compiler_type == "unix":  # type: ignore[attr-defined]
         cflags += ["-O3"]
-        if X86_64:
-            cflags.append("-msse4.2")  # Enable SIMD (see also mypyc/build.py)
-    elif compiler.compiler_type == "msvc":
+    elif compiler.compiler_type == "msvc":  # type: ignore[attr-defined]
         cflags += ["/O2"]
-        if X86_64:
-            cflags.append("/arch:SSE4.2")  # Enable SIMD (see also mypyc/build.py)
 
     setup(
         ext_modules=[

diff --git a/setup.py b/setup.py
@@ -99,6 +99,7 @@ def run(self) -> None:
         os.path.join("mypyc", "lib-rt", "setup.py"),
         # Uses __file__ at top level https://github.com/mypyc/mypyc/issues/700
         os.path.join("mypyc", "__main__.py"),
+        os.path.join("mypyc", "build_setup.py"),  # for monkeypatching
     )
 
     everything = [os.path.join("mypy", x) for x in find_package_data("mypy", ["*.py"])] + [