build: add support for building CUDA files with clang

This avoids using the CUDA SDK at all; instead, we provide a minimal
reimplementation of the basic functionality that lavfi actually uses.
It generates very similar code to what NVCC produces.

The header contains no implementation code derived from the SDK.
The function and type declarations are derived from the SDK only to the
extent required to build a compatible implementation. This is generally
accepted to qualify as fair use.

Because this option does not require the proprietary SDK, it does not require
the "--enable-nonfree" flag in configure.

Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>

4 files changed, 178 insertions, 24 deletions

diff --git a/Changelog b/Changelog
index beb2d2615d..389ca6c4db 100644
--- a/Changelog
+++ b/Changelog
@@ -36,6 +36,7 @@ version 4.2:
 - derain filter
 - deesser filter
 - mov muxer writes tracks with unspecified language instead of English by default
+- add support for using clang to compile CUDA kernels
 
 
 version 4.1:
diff --git a/compat/cuda/cuda_runtime.h b/compat/cuda/cuda_runtime.h
new file mode 100644
index 0000000000..dbe50f8711
--- /dev/null
+++ b/compat/cuda/cuda_runtime.h
@@ -0,0 +1,131 @@
+/*
+ * Minimum CUDA compatibility definitions header
+ *
+ * Copyright (c) 2019 Rodger Combs
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AV_COMPAT_CUDA_CUDA_RUNTIME_H
+#define AV_COMPAT_CUDA_CUDA_RUNTIME_H
+
+// Common macros
+#define __global__ __attribute__((global))
+#define __device__ __attribute__((device))
+#define __device_builtin__ __attribute__((device_builtin))
+#define __align__(N) __attribute__((aligned(N)))
+#define __inline__ __inline__ __attribute__((always_inline))
+
+#define max(a, b) ((a) > (b) ? (a) : (b))
+#define min(a, b) ((a) < (b) ? (a) : (b))
+#define abs(x) ((x) < 0 ? -(x) : (x))
+
+#define atomicAdd(a, b) (__atomic_fetch_add(a, b, __ATOMIC_SEQ_CST))
+
+// Basic typedefs
+typedef __device_builtin__ unsigned long long cudaTextureObject_t;
+
+typedef struct __device_builtin__ __align__(2) uchar2
+{
+    unsigned char x, y;
+} uchar2;
+
+typedef struct __device_builtin__ __align__(4) ushort2
+{
+    unsigned short x, y;
+} ushort2;
+
+typedef struct __device_builtin__ uint3
+{
+    unsigned int x, y, z;
+} uint3;
+
+typedef struct uint3 dim3;
+
+typedef struct __device_builtin__ __align__(8) int2
+{
+    int x, y;
+} int2;
+
+typedef struct __device_builtin__ __align__(4) uchar4
+{
+    unsigned char x, y, z, w;
+} uchar4;
+
+typedef struct __device_builtin__ __align__(8) ushort4
+{
+    unsigned char x, y, z, w;
+} ushort4;
+
+typedef struct __device_builtin__ __align__(16) int4
+{
+    int x, y, z, w;
+} int4;
+
+// Accessors for special registers
+#define GETCOMP(reg, comp) \
+    asm("mov.u32 %0, %%" #reg "." #comp ";" : "=r"(tmp)); \
+    ret.comp = tmp;
+
+#define GET(name, reg) static inline __device__ uint3 name() {\
+    uint3 ret; \
+    unsigned tmp; \
+    GETCOMP(reg, x) \
+    GETCOMP(reg, y) \
+    GETCOMP(reg, z) \
+    return ret; \
+}
+
+GET(getBlockIdx, ctaid)
+GET(getBlockDim, ntid)
+GET(getThreadIdx, tid)
+
+// Instead of externs for these registers, we turn access to them into calls into trivial ASM
+#define blockIdx (getBlockIdx())
+#define blockDim (getBlockDim())
+#define threadIdx (getThreadIdx())
+
+// Basic initializers (simple macros rather than inline functions)
+#define make_uchar2(a, b) ((uchar2){.x = a, .y = b})
+#define make_ushort2(a, b) ((ushort2){.x = a, .y = b})
+#define make_uchar4(a, b, c, d) ((uchar4){.x = a, .y = b, .z = c, .w = d})
+#define make_ushort4(a, b, c, d) ((ushort4){.x = a, .y = b, .z = c, .w = d})
+
+// Conversions from the tex instruction's 4-register output to various types
+#define TEX2D(type, ret) static inline __device__ void conv(type* out, unsigned a, unsigned b, unsigned c, unsigned d) {*out = (ret);}
+
+TEX2D(unsigned char, a & 0xFF)
+TEX2D(unsigned short, a & 0xFFFF)
+TEX2D(uchar2, make_uchar2(a & 0xFF, b & 0xFF))
+TEX2D(ushort2, make_ushort2(a & 0xFFFF, b & 0xFFFF))
+TEX2D(uchar4, make_uchar4(a & 0xFF, b & 0xFF, c & 0xFF, d & 0xFF))
+TEX2D(ushort4, make_ushort4(a & 0xFFFF, b & 0xFFFF, c & 0xFFFF, d & 0xFFFF))
+
+// Template calling tex instruction and converting the output to the selected type
+template <class T>
+static inline __device__ T tex2D(cudaTextureObject_t texObject, float x, float y)
+{
+  T ret;
+  unsigned ret1, ret2, ret3, ret4;
+  asm("tex.2d.v4.u32.f32 {%0, %1, %2, %3}, [%4, {%5, %6}];" :
+      "=r"(ret1), "=r"(ret2), "=r"(ret3), "=r"(ret4) :
+      "l"(texObject), "f"(x), "f"(y));
+  conv(&ret, ret1, ret2, ret3, ret4);
+  return ret;
+}
+
+#endif
diff --git a/configure b/configure
index 5a4f507246..bddc05b850 100755
--- a/configure
+++ b/configure
@@ -322,6 +322,7 @@ External library support:
   --disable-amf            disable AMF video encoding code [autodetect]
   --disable-audiotoolbox   disable Apple AudioToolbox code [autodetect]
   --enable-cuda-nvcc       enable Nvidia CUDA compiler [no]
+  --disable-cuda-llvm      disable CUDA compilation using clang [autodetect]
   --disable-cuvid          disable Nvidia CUVID support [autodetect]
   --disable-d3d11va        disable Microsoft Direct3D 11 video acceleration code [autodetect]
   --disable-dxva2          disable Microsoft DirectX 9 video acceleration code [autodetect]
@@ -370,7 +371,7 @@ Toolchain options:
   --cxx=CXX                use C compiler CXX [$cxx_default]
   --objcc=OCC              use ObjC compiler OCC [$cc_default]
   --dep-cc=DEPCC           use dependency generator DEPCC [$cc_default]
-  --nvcc=NVCC              use Nvidia CUDA compiler NVCC [$nvcc_default]
+  --nvcc=NVCC              use Nvidia CUDA compiler NVCC or clang [$nvcc_default]
   --ld=LD                  use linker LD [$ld_default]
   --pkg-config=PKGCONFIG   use pkg-config tool PKGCONFIG [$pkg_config_default]
   --pkg-config-flags=FLAGS pass additional flags to pkgconf []
@@ -1038,12 +1039,16 @@ test_nvcc(){
     tmpcu_=$TMPCU
     tmpo_=$TMPO
     [ -x "$(command -v cygpath)" ] && tmpcu_=$(cygpath -m $tmpcu_) && tmpo_=$(cygpath -m $tmpo_)
-    test_cmd $nvcc -ptx $NVCCFLAGS "$@" $NVCC_C $(nvcc_o $tmpo_) $tmpcu_
+    test_cmd $nvcc $nvccflags "$@" $NVCC_C $(nvcc_o $tmpo_) $tmpcu_
 }
 
 check_nvcc() {
     log check_nvcc "$@"
-    test_nvcc <<EOF
+    name=$1
+    shift 1
+    disabled $name && return
+    disable $name
+    test_nvcc "$@" <<EOF && enable $name
 extern "C" {
     __global__ void hello(unsigned char *data) {}
 }
@@ -1814,6 +1819,7 @@ HWACCEL_AUTODETECT_LIBRARY_LIST="
     audiotoolbox
     crystalhd
     cuda
+    cuda_llvm
     cuvid
     d3d11va
     dxva2
@@ -2987,8 +2993,10 @@ v4l2_m2m_deps="linux_videodev2_h sem_timedwait"
 
 hwupload_cuda_filter_deps="ffnvcodec"
 scale_npp_filter_deps="ffnvcodec libnpp"
-scale_cuda_filter_deps="ffnvcodec cuda_nvcc"
-thumbnail_cuda_filter_deps="ffnvcodec cuda_nvcc"
+scale_cuda_filter_deps="ffnvcodec"
+scale_cuda_filter_deps_any="cuda_nvcc cuda_llvm"
+thumbnail_cuda_filter_deps="ffnvcodec"
+thumbnail_cuda_filter_deps_any="cuda_nvcc cuda_llvm"
 transpose_npp_filter_deps="ffnvcodec libnpp"
 
 amf_deps_any="libdl LoadLibrary"
@@ -3547,7 +3555,8 @@ zscale_filter_deps="libzimg const_nan"
 scale_vaapi_filter_deps="vaapi"
 vpp_qsv_filter_deps="libmfx"
 vpp_qsv_filter_select="qsvvpp"
-yadif_cuda_filter_deps="ffnvcodec cuda_nvcc"
+yadif_cuda_filter_deps="ffnvcodec"
+yadif_cuda_filter_deps_any="cuda_nvcc cuda_llvm"
 
 # examples
 avio_dir_cmd_deps="avformat avutil"
@@ -3651,8 +3660,6 @@ version_script='--version-script'
 objformat="elf32"
 x86asmexe_default="nasm"
 windres_default="windres"
-nvcc_default="nvcc"
-nvccflags_default="-gencode arch=compute_30,code=sm_30 -O2"
 striptype="direct"
 
 # OS
@@ -4220,6 +4227,20 @@ windres_default="${cross_prefix}${windres_default}"
 
 sysinclude_default="${sysroot}/usr/include"
 
+if enabled cuda_sdk; then
+    warn "Option --enable-cuda-sdk is deprecated. Use --enable-cuda-nvcc instead."
+    enable cuda_nvcc
+fi
+
+if enabled cuda_nvcc; then
+    nvcc_default="nvcc"
+    nvccflags_default="-gencode arch=compute_30,code=sm_30 -O2"
+else
+    nvcc_default="clang"
+    nvccflags_default="--cuda-gpu-arch=sm_30 -O2"
+    NVCC_C=""
+fi
+
 set_default arch cc cxx doxygen pkg_config ranlib strip sysinclude \
     target_exec x86asmexe nvcc
 enabled cross_compile || host_cc_default=$cc
@@ -6060,9 +6081,21 @@ check_type "d3d9.h dxva2api.h" DXVA2_ConfigPictureDecode -D_WIN32_WINNT=0x0602
 
 check_type "vdpau/vdpau.h" "VdpPictureInfoHEVC"
 
-if enabled cuda_sdk; then
-    warn "Option --enable-cuda-sdk is deprecated. Use --enable-cuda-nvcc instead."
-    enable cuda_nvcc
+if [ -z "$nvccflags" ]; then
+    nvccflags=$nvccflags_default
+fi
+
+if enabled x86_64 || enabled ppc64 || enabled aarch64; then
+    nvccflags="$nvccflags -m64"
+else
+    nvccflags="$nvccflags -m32"
+fi
+
+if enabled cuda_nvcc; then
+    nvccflags="$nvccflags -ptx"
+else
+    nvccflags="$nvccflags -S -nocudalib -nocudainc --cuda-device-only -include${source_link}/compat/cuda/cuda_runtime.h"
+    check_nvcc cuda_llvm
 fi
 
 if ! disabled ffnvcodec; then
@@ -6140,7 +6173,7 @@ for func in $COMPLEX_FUNCS; do
 done
 
 # these are off by default, so fail if requested and not available
-enabled cuda_nvcc         && { check_nvcc || die "ERROR: failed checking for nvcc."; }
+enabled cuda_nvcc         && { check_nvcc cuda_nvcc || die "ERROR: failed checking for nvcc."; }
 enabled chromaprint       && require chromaprint chromaprint.h chromaprint_get_version -lchromaprint
 enabled decklink          && { require_headers DeckLinkAPI.h &&
                                { test_cpp_condition DeckLinkAPIVersion.h "BLACKMAGIC_DECKLINK_API_VERSION >= 0x0a090500" || die "ERROR: Decklink API version must be >= 10.9.5."; } }
@@ -6701,16 +6734,6 @@ if [ -z "$optflags" ]; then
     fi
 fi
 
-if [ -z "$nvccflags" ]; then
-    nvccflags=$nvccflags_default
-fi
-
-if enabled x86_64 || enabled ppc64 || enabled aarch64; then
-    nvccflags="$nvccflags -m64"
-else
-    nvccflags="$nvccflags -m32"
-fi
-
 check_optflags(){
     check_cflags "$@"
     enabled lto && check_ldflags "$@"
diff --git a/ffbuild/common.mak b/ffbuild/common.mak
index d2b33320c0..7355508ea0 100644
--- a/ffbuild/common.mak
+++ b/ffbuild/common.mak
@@ -38,7 +38,6 @@ OBJCCFLAGS  = $(CPPFLAGS) $(CFLAGS) $(OBJCFLAGS)
 ASFLAGS    := $(CPPFLAGS) $(ASFLAGS)
 CXXFLAGS   := $(CPPFLAGS) $(CFLAGS) $(CXXFLAGS)
 X86ASMFLAGS += $(IFLAGS:%=%/) -I$(<D)/ -Pconfig.asm
-NVCCFLAGS  += -ptx
 
 HOSTCCFLAGS = $(IFLAGS) $(HOSTCPPFLAGS) $(HOSTCFLAGS)
 LDFLAGS    := $(ALLFFLIBS:%=$(LD_PATH)lib%) $(LDFLAGS)
@@ -91,7 +90,7 @@ COMPILE_NVCC = $(call COMPILE,NVCC)
 %.h.c:
 	$(Q)echo '#include "$*.h"' >$@
 
-%.ptx: %.cu
+%.ptx: %.cu $(SRC_PATH)/compat/cuda/cuda_runtime.h
 	$(COMPILE_NVCC)
 
 %.ptx.c: %.ptx