aarch64/vvc: Fix DCE undefined references with MSVC

mstorsjo · mstorsjo · commit 74cfcd1c6912 · 2026-03-05T11:57:40.000+02:00
This fixes compiling with MSVC for aarch64 after 510999f. While MSVC does do dead code elimintation for function references within e.g. "if (0)", it doesn't do that for functions referenced within a static function, even if that static function itself ends up not used. A reproduction example: void missing(void); void (*func_ptr)(void); static void wrapper(void) { missing(); } void init(int cpu_flags) { if (0) { func_ptr = wrapper; } } If "wrapper" is entirely unreferenced, then MSVC doesn't produce any reference to the symbol "missing". Also, if we do "func_ptr = missing;" then the reference to missing also is eliminated. But for the case of referencing the function in a static function, even if the reference to the static function can be eliminated, then MSVC does keep the reference to the symbol.
diff --git a/libavcodec/aarch64/vvc/alf_template.c b/libavcodec/aarch64/vvc/alf_template.c
@@ -259,10 +259,15 @@ static void FUNC2(alf_filter_luma, BIT_DEPTH, _sme2)(uint8_t *_dst,
                                                      const int vb_pos)
 {
     if ((width >= 16) && (height >= 16)) {
+        // If compiled without support for SME2 or SME-I16I64, we never assign
+        // the function pointer anyway, but make sure we don't produce a
+        // reference to the function which does not exist.
+#if HAVE_SME2 && HAVE_SME_I16I64
         int aligned_width = ALF_ALIGN_BY_4(width); // align width by 4
         uint64_t dims = ((uint64_t)height << 32u) | (uint64_t)aligned_width;
         uint64_t strides = ((uint64_t)src_stride << 32u) | (uint64_t)dst_stride;
         FUNC2(ff_vvc_alf_filter_luma, BIT_DEPTH, _sme2)(_dst, _src, strides, dims, filter, clip, vb_pos);
+#endif
     } else {
         FUNC2(alf_filter_luma, BIT_DEPTH, _neon)(_dst, dst_stride, _src, src_stride, width, height, filter, clip, vb_pos);
     }
