all: Replace if (ARCH_FOO) checks by #if ARCH_FOO

This is more spec-compliant because it does not rely
on dead-code elimination by the compiler. Especially
MSVC has problems with this, as can be seen in
https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/296373.html
or
https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/297022.html

This commit does not eliminate every instance where we rely
on dead code elimination: It only tackles branching to
the initialization of arch-specific dsp code, not e.g. all
uses of CONFIG_ and HAVE_ checks. But maybe it is already
enough to compile FFmpeg with MSVC with whole-programm-optimizations
enabled (if one does not disable too many components).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

1 files changed, 14 insertions, 13 deletions

diff --git a/libavcodec/pixblockdsp.c b/libavcodec/pixblockdsp.c
index 67393b9593..17c487da1e 100644
--- a/libavcodec/pixblockdsp.c
+++ b/libavcodec/pixblockdsp.c
@@ -80,7 +80,7 @@ static void diff_pixels_c(int16_t *av_restrict block, const uint8_t *s1,
 
 av_cold void ff_pixblockdsp_init(PixblockDSPContext *c, AVCodecContext *avctx)
 {
-    const unsigned high_bit_depth = avctx->bits_per_raw_sample > 8;
+    av_unused const unsigned high_bit_depth = avctx->bits_per_raw_sample > 8;
 
     c->diff_pixels_unaligned =
     c->diff_pixels = diff_pixels_c;
@@ -101,16 +101,17 @@ av_cold void ff_pixblockdsp_init(PixblockDSPContext *c, AVCodecContext *avctx)
         break;
     }
 
-    if (ARCH_AARCH64)
-        ff_pixblockdsp_init_aarch64(c, avctx, high_bit_depth);
-    if (ARCH_ALPHA)
-        ff_pixblockdsp_init_alpha(c, avctx, high_bit_depth);
-    if (ARCH_ARM)
-        ff_pixblockdsp_init_arm(c, avctx, high_bit_depth);
-    if (ARCH_PPC)
-        ff_pixblockdsp_init_ppc(c, avctx, high_bit_depth);
-    if (ARCH_X86)
-        ff_pixblockdsp_init_x86(c, avctx, high_bit_depth);
-    if (ARCH_MIPS)
-        ff_pixblockdsp_init_mips(c, avctx, high_bit_depth);
+#if ARCH_AARCH64
+    ff_pixblockdsp_init_aarch64(c, avctx, high_bit_depth);
+#elif ARCH_ALPHA
+    ff_pixblockdsp_init_alpha(c, avctx, high_bit_depth);
+#elif ARCH_ARM
+    ff_pixblockdsp_init_arm(c, avctx, high_bit_depth);
+#elif ARCH_PPC
+    ff_pixblockdsp_init_ppc(c, avctx, high_bit_depth);
+#elif ARCH_X86
+    ff_pixblockdsp_init_x86(c, avctx, high_bit_depth);
+#elif ARCH_MIPS
+    ff_pixblockdsp_init_mips(c, avctx, high_bit_depth);
+#endif
 }