From 6f74fb03cde1266feea8882d5b672e827ad8f55b Mon Sep 17 00:00:00 2001
From: Ramiro Polla <ramiro.polla@gmail.com>
Date: Wed, 6 Oct 2010 01:26:13 +0000
Subject: [PATCH] Check whether compiler supports xmm registers in asm clobber
 list

Originally committed as revision 25362 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 configure           |  4 ++++
 libavutil/x86_cpu.h | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/configure b/configure
index 7fa99da7cc..607a180973 100755
--- a/configure
+++ b/configure
@@ -1074,6 +1074,7 @@ HAVE_LIST="
     VirtualAlloc
     winsock2_h
     xform_asm
+    xmm_clobbers
     yasm
 "
 
@@ -2585,6 +2586,9 @@ EOF
     check_asm ebx_available '""::"b"(0)' &&
         check_asm ebx_available '"":::"%ebx"'
 
+    # check whether xmm clobbers are supported
+    check_asm xmm_clobbers '"":::"%xmm0"'
+
     # check whether more than 10 operands are supported
     check_cc <<EOF && enable ten_operands
 int main(void) {
diff --git a/libavutil/x86_cpu.h b/libavutil/x86_cpu.h
index b1b7d8b978..c3341c232d 100644
--- a/libavutil/x86_cpu.h
+++ b/libavutil/x86_cpu.h
@@ -75,4 +75,24 @@ typedef int x86_reg;
 #    define BROKEN_RELOCATIONS 1
 #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
+ * 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 xmm
+ * registers are the only in the clobber list.
+ * For example a list with "eax" and "xmm0" as clobbers should become:
+ * : XMM_CLOBBERS("xmm0",) "eax"
+ * and a list with only "xmm0" should become:
+ * XMM_CLOBBERS_ONLY("xmm0")
+ */
+#if HAVE_XMM_CLOBBERS
+#    define XMM_CLOBBERS(...)        __VA_ARGS__
+#    define XMM_CLOBBERS_ONLY(...) : __VA_ARGS__
+#else
+#    define XMM_CLOBBERS(...)
+#    define XMM_CLOBBERS_ONLY(...)
+#endif
+
 #endif /* AVUTIL_X86_CPU_H */