[FFmpeg-devel] [PATCH 3/5] [inline assembly] prepares for mmx clobbers akin to xmm

[frederic.recoules at univ-grenoble-alpes.fr]

From: Frédéric Recoules <frederic.recoules at orange.fr>

---
 configure           |  4 ++++
 libavutil/x86/asm.h | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/configure b/configure
index 6533b43250..ddfea5ccfa 100755
--- a/configure
+++ b/configure
@@ -2275,6 +2275,7 @@ TOOLCHAIN_FEATURES="
     symver_gnu_asm
     vfp_args
     xform_asm
+    mmx_clobbers
     xmm_clobbers
 "
 
@@ -5917,6 +5918,9 @@ EOF
     check_inline_asm ebx_available '""::"b"(0)' &&
         check_inline_asm ebx_available '"":::"%ebx"'
 
+    # check whether mmx clobbers are supported
+    check_inline_asm mmx_clobbers '"":::"%mm0"'
+
     # check whether xmm clobbers are supported
     check_inline_asm xmm_clobbers '"":::"%xmm0"'
 
diff --git a/libavutil/x86/asm.h b/libavutil/x86/asm.h
index 9bff42d628..bb3c13f5c1 100644
--- a/libavutil/x86/asm.h
+++ b/libavutil/x86/asm.h
@@ -79,6 +79,26 @@ typedef int x86_reg;
 #    define BROKEN_RELOCATIONS 1
 #endif
 
+/*
+ * If gcc is not set to support mmx (-mmmx) it will not accept mmx registers
+ * in the clobber list for inline asm. MMX_CLOBBERS takes a list of mmx
+ * registers to be marked as clobbered and evaluates to nothing if they are
+ * not supported, or to the list itself if they are supported. Since a clobber
+ * list may not be empty, XMM_CLOBBERS_ONLY should be used if the mmx
+ * registers are the only in the clobber list.
+ * For example a list with "eax" and "mm0" as clobbers should become:
+ * : MMX_CLOBBERS("mm0",) "eax"
+ * and a list with only "mm0" should become:
+ * MMX_CLOBBERS_ONLY("mm0")
+ */
+#if HAVE_MMX_CLOBBERS
+#    define MMX_CLOBBERS(...)        __VA_ARGS__
+#    define MMX_CLOBBERS_ONLY(...) : __VA_ARGS__
+#else
+#    define MMX_CLOBBERS(...)
+#    define MMX_CLOBBERS_ONLY(...)
+#endif
+
 /*
  * If gcc is not set to support sse (-msse) it will not accept xmm registers
  * in the clobber list for inline asm. XMM_CLOBBERS takes a list of xmm
-- 
2.17.1