build: Prefer NASM assembler over YASM

NASM is more actively maintained and permits generating dependency information
as a sideeffect of assembling, thus cutting build times in half.

(Cherry-picked from libav commit 57b753b4)
Signed-off-by: James Almer <jamrial@gmail.com>

.travis.yml

@@ -6,7 +6,7 @@ os:
 addons:
   apt:
     packages:
-      - yasm
+      - nasm
       - diffutils
 compiler:
   - clang
@@ -17,7 +17,7 @@ cache:
 before_install:
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update --all; fi
 install:
-  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install yasm; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install nasm; fi
 script:
   - mkdir -p ffmpeg-samples
   - ./configure --samples=ffmpeg-samples --cc=$CC

Changelog

@@ -22,6 +22,8 @@ version <next>:
 - headphone audio filter
 - superequalizer audio filter
 - roberts video filter
+- The x86 assembler default switched from yasm to nasm, pass
+  --x86asmexe=yasm to configure to restore the old behavior.
 
 version 3.3:
 - CrystalHD decoder moved to new decode API

configure

@@ -3258,7 +3258,7 @@ pkg_config_default=pkg-config
 ranlib_default="ranlib"
 strip_default="strip"
 version_script='--version-script'
-x86asmexe_default="yasm"
+x86asmexe_default="nasm"
 windres_default="windres"
 nvcc_default="nvcc"
 nvccflags_default="-gencode arch=compute_30,code=sm_30 -O2"
@@ -5506,7 +5506,7 @@ EOF
     }
 
     if ! disabled_any asm mmx x86asm; then
-        for program in $x86asmexe yasm nasm; do
+        for program in $x86asmexe nasm yasm; do
             probe_x86asm $program
             test -n "$x86asm_type" && break
         done
@@ -5518,7 +5518,7 @@ EOF
         esac
 
         check_x86asm "movbe ecx, [5]" && enable x86asm ||
-            die "yasm/nasm not found or too old. Use --disable-x86asm for a crippled build."
+            die "nasm/yasm not found or too old. Use --disable-x86asm for a crippled build."
         check_x86asm "vextracti128 xmm0, ymm0, 0"      || disable avx2_external
         check_x86asm "vpmacsdd xmm0, xmm1, xmm2, xmm3" || disable xop_external
         check_x86asm "vfmaddps ymm0, ymm1, ymm2, ymm3" || disable fma4_external

doc/optimization.txt

@@ -161,8 +161,8 @@ do{
 For x86, mark registers that are clobbered in your asm. This means both
 general x86 registers (e.g. eax) as well as XMM registers. This last one is
 particularly important on Win64, where xmm6-15 are callee-save, and not
-restoring their contents leads to undefined results. In external asm (e.g.
-yasm), you do this by using:
+restoring their contents leads to undefined results. In external asm,
+you do this by using:
 cglobal function_name, num_args, num_regs, num_xmm_regs
 In inline asm, you specify clobbered registers at the end of your asm:
 __asm__(".." ::: "%eax").
@@ -199,12 +199,12 @@ actual lines causing issues.
 Inline asm vs. external asm
 ---------------------------
 Both inline asm (__asm__("..") in a .c file, handled by a compiler such as gcc)
-and external asm (.s or .asm files, handled by an assembler such as yasm/nasm)
+and external asm (.s or .asm files, handled by an assembler such as nasm/yasm)
 are accepted in FFmpeg. Which one to use differs per specific case.
 
 - if your code is intended to be inlined in a C function, inline asm is always
    better, because external asm cannot be inlined
-- if your code calls external functions, yasm is always better
+- if your code calls external functions, external asm is always better
 - if your code takes huge and complex structs as function arguments (e.g.
    MpegEncContext; note that this is not ideal and is discouraged if there
    are alternatives), then inline asm is always better, because predicting

doc/platform.texi

@@ -71,9 +71,9 @@ Mac OS X on PowerPC or ARM (iPhone) requires a preprocessor from
 assembly functions. Put the Perl script somewhere
 in your PATH, FFmpeg's configure will pick it up automatically.
 
-Mac OS X on amd64 and x86 requires @command{yasm} to build most of the
+Mac OS X on amd64 and x86 requires @command{nasm} to build most of the
 optimized assembly functions. @uref{http://www.finkproject.org/, Fink},
-@uref{http://www.gentoo.org/proj/en/gentoo-alt/prefix/bootstrap-macos.xml, Gentoo Prefix},
+@uref{https://wiki.gentoo.org/wiki/Project:Prefix, Gentoo Prefix},
 @uref{https://mxcl.github.com/homebrew/, Homebrew}
 or @uref{http://www.macports.org, MacPorts} can easily provide it.
 
@@ -141,7 +141,7 @@ them under @command{MinGW-w64 Win64 Shell} and @command{MinGW-w64 Win32 Shell}.
 pacman -S make pkgconf diffutils
 
 # mingw-w64 packages and toolchains
-pacman -S mingw-w64-x86_64-yasm mingw-w64-x86_64-gcc mingw-w64-x86_64-SDL
+pacman -S mingw-w64-x86_64-nasm mingw-w64-x86_64-gcc mingw-w64-x86_64-SDL2
 @end example
 
 To target 32 bits replace @code{x86_64} with @code{i686} in the command above.
@@ -159,7 +159,7 @@ You will need the following prerequisites:
 @item @uref{http://code.google.com/p/msinttypes/, msinttypes}
 (if using MSVC 2012 or earlier)
 @item @uref{http://msys2.github.io/, MSYS2}
-@item @uref{http://yasm.tortall.net/, YASM}
+@item @uref{http://www.nasm.us/, NASM}
 (Also available via MSYS2's package manager.)
 @end itemize