[FFmpeg-devel] [PATCH 01/31] lavu/cpu: detect RISC-V base extensions

[remi@remlab.net]

From: Rémi Denis-Courmont <remi@remlab.net>

This introduces compile-time and run-time CPU detection on RISC-V. In
practice, I doubt that FFmpeg will ever see a RISC-V CPU without all of
I, F and D extensions, and if it does, it probably won't have run-time
detection. So the flags are essentially always set.

But as things stand, checkasm wants them that way. Compare the ARMV8
flag on AArch64. We are nowhere near running short on CPU flag bits.
---
 libavutil/cpu.c           |  9 ++++++
 libavutil/cpu.h           |  5 +++
 libavutil/cpu_internal.h  |  3 ++
 libavutil/riscv/Makefile  |  1 +
 libavutil/riscv/cpu.c     | 66 +++++++++++++++++++++++++++++++++++++++
 tests/checkasm/checkasm.c |  4 +++
 6 files changed, 88 insertions(+)
 create mode 100644 libavutil/riscv/Makefile
 create mode 100644 libavutil/riscv/cpu.c

diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index 0035e927a5..78e92a1bf6 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -62,6 +62,8 @@ static int get_cpu_flags(void)
     return ff_get_cpu_flags_arm();
 #elif ARCH_PPC
     return ff_get_cpu_flags_ppc();
+#elif ARCH_RISCV
+    return ff_get_cpu_flags_riscv();
 #elif ARCH_X86
     return ff_get_cpu_flags_x86();
 #elif ARCH_LOONGARCH
@@ -95,6 +97,9 @@ void av_force_cpu_flags(int arg){
         arg |= AV_CPU_FLAG_MMX;
     }
 
+#if ARCH_RISCV
+    arg = ff_force_cpu_flags_riscv(arg);
+#endif
     atomic_store_explicit(&cpu_flags, arg, memory_order_relaxed);
 }
 
@@ -178,6 +183,10 @@ int av_parse_cpu_caps(unsigned *flags, const char *s)
 #elif ARCH_LOONGARCH
         { "lsx",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_LSX      },    .unit = "flags" },
         { "lasx",     NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_LASX     },    .unit = "flags" },
+#elif ARCH_RISCV
+        { "rvi",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_RVI      },    .unit = "flags" },
+        { "rvf",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_RVF      },    .unit = "flags" },
+        { "rvd",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_RVD      },    .unit = "flags" },
 #endif
         { NULL },
     };
diff --git a/libavutil/cpu.h b/libavutil/cpu.h
index 9711e574c5..9aae2ccc7a 100644
--- a/libavutil/cpu.h
+++ b/libavutil/cpu.h
@@ -78,6 +78,11 @@
 #define AV_CPU_FLAG_LSX          (1 << 0)
 #define AV_CPU_FLAG_LASX         (1 << 1)
 
+// RISC-V extensions
+#define AV_CPU_FLAG_RVI          (1 << 0) ///< I (full GPR bank)
+#define AV_CPU_FLAG_RVF          (1 << 1) ///< F (single precision FP)
+#define AV_CPU_FLAG_RVD          (1 << 2) ///< D (double precision FP)
+
 /**
  * Return the flags which specify extensions supported by the CPU.
  * The returned value is affected by av_force_cpu_flags() if that was used
diff --git a/libavutil/cpu_internal.h b/libavutil/cpu_internal.h
index 650d47fc96..9ddf11488b 100644
--- a/libavutil/cpu_internal.h
+++ b/libavutil/cpu_internal.h
@@ -48,9 +48,12 @@ int ff_get_cpu_flags_mips(void);
 int ff_get_cpu_flags_aarch64(void);
 int ff_get_cpu_flags_arm(void);
 int ff_get_cpu_flags_ppc(void);
+int ff_get_cpu_flags_riscv(void);
 int ff_get_cpu_flags_x86(void);
 int ff_get_cpu_flags_loongarch(void);
 
+int ff_force_cpu_flags_riscv(int flags);
+
 size_t ff_get_cpu_max_align_mips(void);
 size_t ff_get_cpu_max_align_aarch64(void);
 size_t ff_get_cpu_max_align_arm(void);
diff --git a/libavutil/riscv/Makefile b/libavutil/riscv/Makefile
new file mode 100644
index 0000000000..1f818043dc
--- /dev/null
+++ b/libavutil/riscv/Makefile
@@ -0,0 +1 @@
+OBJS += riscv/cpu.o
diff --git a/libavutil/riscv/cpu.c b/libavutil/riscv/cpu.c
new file mode 100644
index 0000000000..fec1f7822a
--- /dev/null
+++ b/libavutil/riscv/cpu.c
@@ -0,0 +1,66 @@
+/*
+ * Copyright © 2022 Rémi Denis-Courmont.
+ *
+ * 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
+ */
+
+#include "libavutil/cpu.h"
+#include "libavutil/cpu_internal.h"
+#include "libavutil/log.h"
+#include "config.h"
+
+#if HAVE_GETAUXVAL
+#include <sys/auxv.h>
+#define HWCAP_RV(letter) (1ul << ((letter) - 'A'))
+#endif
+
+int ff_force_cpu_flags_riscv(int flags)
+{
+    if ((flags & AV_CPU_FLAG_RVD) && !(flags & AV_CPU_FLAG_RVF)) {
+        av_log(NULL, AV_LOG_WARNING, "RV%s implied by specified flags\n", "F");
+        flags |= AV_CPU_FLAG_RVF;
+    }
+
+    return flags;
+}
+
+int ff_get_cpu_flags_riscv(void)
+{
+    int ret = 0;
+#if HAVE_GETAUXVAL
+    const unsigned long hwcap = getauxval(AT_HWCAP);
+
+    if (hwcap & HWCAP_RV('I'))
+        ret |= AV_CPU_FLAG_RVI;
+    if (hwcap & HWCAP_RV('F'))
+        ret |= AV_CPU_FLAG_RVF;
+    if (hwcap & HWCAP_RV('D'))
+        ret |= AV_CPU_FLAG_RVD;
+#endif
+
+#ifdef __riscv_i
+    ret |= AV_CPU_FLAG_RVI;
+#endif
+#if defined (__riscv_flen) && (__riscv_flen >= 32)
+    ret |= AV_CPU_FLAG_RVF;
+#if (__riscv_flen >= 64)
+    ret |= AV_CPU_FLAG_RVD;
+#endif
+#endif
+
+    return ret;
+}
diff --git a/tests/checkasm/checkasm.c b/tests/checkasm/checkasm.c
index 8fd9bba0b0..e1135a84ac 100644
--- a/tests/checkasm/checkasm.c
+++ b/tests/checkasm/checkasm.c
@@ -232,6 +232,10 @@ static const struct {
     { "ALTIVEC",  "altivec",  AV_CPU_FLAG_ALTIVEC },
     { "VSX",      "vsx",      AV_CPU_FLAG_VSX },
     { "POWER8",   "power8",   AV_CPU_FLAG_POWER8 },
+#elif ARCH_RISCV
+    { "RVI",      "rvi",      AV_CPU_FLAG_RVI },
+    { "RVF",      "rvf",      AV_CPU_FLAG_RVF },
+    { "RVD",      "rvd",      AV_CPU_FLAG_RVD },
 #elif ARCH_MIPS
     { "MMI",      "mmi",      AV_CPU_FLAG_MMI },
     { "MSA",      "msa",      AV_CPU_FLAG_MSA },
-- 
2.37.2

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