Build: Clarify comment in configure.ac about SSE2.

diff --git a/configure.ac b/configure.ac
index 9d851073d7b96c6e909cfee4f371ab761441cedc..af82adebc0e62157421170fae51ab11e5e60de66 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -797,7 +797,10 @@ if test "x$enable_external_sha256$sha256_func_found" = xyesno; then
        AC_MSG_ERROR([--enable-external-sha256 was specified but no supported external SHA-256 implementation was found])
 fi
 
-# Check for SSE2 intrinsics.
+# Check for SSE2 intrinsics. There is no run-time detection for SSE2 so if
+# compiler options enable SSE2 then SSE2 support is required by the binaries.
+# The compile-time check for SSE2 is done with #ifdefs because some compilers
+# (ICC, MSVC) allow SSE2 intrinsics even when SSE2 isn't enabled.
 AC_CHECK_DECL([_mm_movemask_epi8],
        [AC_DEFINE([HAVE__MM_MOVEMASK_EPI8], [1],
                [Define to 1 if _mm_movemask_epi8 is available.])],