cmake: use TargetConditionals.h for SIMD testing on Apple

[madebr]

I think include/SDL3/SDL_intrin.h should get a similar makeover.

[sezero]

Looked OK to be after brief eyeballing.

[madebr]

This actions run behaves as expected now: https://github.com/libsdl-org/SDL/actions/runs/14251280259/job/39944568381?pr=12731

• it uses -DCMAKE_OSX_ARCHITECTURES=x86_64;arm64
• all simd extensions (mmx, sse, avx, neon) are supported, so no #define SDL_DISABLE_xxx's in the generated SDL_build_config.h

[madebr]

An Apple person should check whether the SDL_intrin.h behaves as expected.
The header would need this, and perhaps additional changes.

--- a/include/SDL3/SDL_intrin.h
+++ b/include/SDL3/SDL_intrin.h
@@ -356,7 +356,11 @@ _m_prefetch(void *__P)
 # endif
 #endif
 
-#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86)
+#ifdef __APPLE__
+#include "TargetConditionals.h"
+#endif
+
+#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86) || (defined(TARGET_CPU_X86) && TARGET_CPU_X86) || (defined(TARGET_CPU_X86_64) && TARGET_CPU_X86_64)
 # if ((defined(_MSC_VER) && !defined(_M_X64)) || defined(__MMX__) || defined(SDL_HAS_TARGET_ATTRIBS)) && !defined(SDL_DISABLE_MMX)
 #  define SDL_MMX_INTRINSICS 1
 #  include <mmintrin.h>

[sezero]

An Apple person should check whether the SDL_intrin.h behaves as expected. The header would need this, and perhaps additional changes.

--- a/include/SDL3/SDL_intrin.h
+++ b/include/SDL3/SDL_intrin.h
@@ -356,7 +356,11 @@ _m_prefetch(void *__P)
 # endif
 #endif
 
-#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86)
+#ifdef __APPLE__
+#include "TargetConditionals.h"
+#endif
+
+#if defined(__x86_64__) || defined(_M_X64) || defined(__i386__) || defined(_M_IX86) || (defined(TARGET_CPU_X86) && TARGET_CPU_X86) || (defined(TARGET_CPU_X86_64) && TARGET_CPU_X86_64)
 # if ((defined(_MSC_VER) && !defined(_M_X64)) || defined(__MMX__) || defined(SDL_HAS_TARGET_ATTRIBS)) && !defined(SDL_DISABLE_MMX)
 #  define SDL_MMX_INTRINSICS 1
 #  include <mmintrin.h>

I don't think this is necessary: TARGET_CPU_X86, for, e.g., is defined to 1 if __i386__ is defined (otherwise to 0). Similarly, TARGET_CPU_X86_64 is defined to 1 if __x86_64__ is defined (otherwise to 0). In short, we are already covering those cases here. Am I missing something?

[madebr]

I don't think this is necessary: TARGET_CPU_X86, for, e.g., is defined to 1 if __i386__ is defined (otherwise to 0). Similarly, TARGET_CPU_X86_64 is defined to 1 if __x86_64__ is defined (otherwise to 0). In short, we are already covering those cases here. Am I missing something?

I think we're fine. After thinking about it, CMake was failing because we were including <xmmintrin.h> when targeting arm64.

[sezero]

If I'm reading this correctly, this x86 test will succeed for aarch64-apple (non-x86.) Similarly, the arm test below will succeed for x86_64-apple (non-arm.) Is this what you really intend?

[madebr]

These functions will only get called if cmake is targeting x64/x86.
I'll add a fail-safe that returns false when the cpu is not x86 (and vice verse for the arm function)