riscv: Simplify the runtime check to always be present

Signed-off-by: Cosmin Truta <ctruta@gmail.com>

CMakeLists.txt

@@ -322,9 +322,9 @@ if(PNG_HARDWARE_OPTIMIZATIONS)
   # Set definitions and sources for RISC-V.
   if(PNG_TARGET_ARCHITECTURE MATCHES "^(riscv)")
     include(CheckCCompilerFlag)
-    set(PNG_RISCV_RVV_POSSIBLE_VALUES check on off)
+    set(PNG_RISCV_RVV_POSSIBLE_VALUES on off)
     set(PNG_RISCV_RVV "off"
-      CACHE STRING "Enable RISC-V Vector optimizations: check|on|off; off is default")
+      CACHE STRING "Enable RISC-V Vector optimizations: on|off; off is default")
     set_property(CACHE PNG_RISCV_RVV
                 PROPERTY STRINGS ${PNG_RISCV_RVV_POSSIBLE_VALUES})
     list(FIND PNG_RISCV_RVV_POSSIBLE_VALUES ${PNG_RISCV_RVV} index)
@@ -354,9 +354,8 @@ if(PNG_HARDWARE_OPTIMIZATIONS)
           riscv/riscv_init.c)
       if(PNG_RISCV_RVV STREQUAL "on")
         add_definitions(-DPNG_RISCV_RVV_OPT=2)
-      elseif(PNG_RISCV_RVV STREQUAL "check")
+      else()
-        add_definitions(-DPNG_RISCV_RVV_CHECK_SUPPORTED)
+        add_definitions(-DPNG_RISCV_RVV_OPT=0)
-        add_definitions(-DPNG_RISCV_RVV_OPT=1)
       endif()
     else()
       add_definitions(-DPNG_RISCV_RVV_OPT=0)

configure.ac

@@ -679,8 +679,7 @@ AS_HELP_STRING([[[--enable-riscv-rvv]]],
       [Enable RISC-V Vector optimizations: =no/off, check, api, yes/on:]
       [no/off: disable the optimizations; check: use internal checking code]
       [api: disable by default, enable by a call to png_set_option]
-      [yes/on: turn on unconditionally.]
+      [yes/on: turn on. If not specified: determined by the compiler.]),
-      [If not specified: determined by the compiler.]),
    [case "$enableval" in
       no|off)
          # disable the default enabling on __riscv systems:
@@ -688,20 +687,11 @@ AS_HELP_STRING([[[--enable-riscv-rvv]]],
                    [Disable RISC-V Vector optimizations])
          # Prevent inclusion of the platform-specific files below:
          enable_riscv_rvv=no ;;
-      check)
-         AC_DEFINE([PNG_RISCV_RVV_CHECK_SUPPORTED], [],
-                   [Check for RISC-V Vector support at run-time])
-         AC_MSG_WARN([--enable-riscv-rvv Please check contrib/riscv-rvv/README file]
-            [for the list of supported OSes.]);;
-      api)
-         AC_DEFINE([PNG_RISCV_RVV_API_SUPPORTED], [],
-                   [Turn on RISC-V Vector optimizations at run-time]);;
       yes|on)
          AC_DEFINE([PNG_RISCV_RVV_OPT], [2],
                    [Enable RISC-V Vector optimizations])
-         AC_MSG_WARN([--enable-riscv-rvv: please specify 'check' or 'api', if]
+         AC_MSG_WARN([--enable-riscv-rvv:]
-            [you want the optimizations unconditionally pass e.g. '-march=rv64gv1p0']
+            [if you want the optimizations pass e.g. '-march=rv64gv1p0' to the compiler.]);;
-            [to the compiler.]);;
       *)
          AC_MSG_ERROR([--enable-riscv-rvv=${enable_riscv_rvv}: invalid value])
    esac])

riscv/riscv_init.c

@@ -16,20 +16,6 @@
 
 #include <riscv_vector.h>
 
-#ifdef PNG_RISCV_RVV_CHECK_SUPPORTED /* Do run-time checks */
-/* WARNING: it is strongly recommended that you do not build libpng with
- * run-time checks for CPU features if at all possible. In the case of the
- * RISC-V Vector instructions there is no processor-specific way of detecting
- * the presence of the required support, therefore run-time detection is
- * extremely OS specific.
- *
- * You may set the macro PNG_RISCV_RVV_FILE to the file name of file containing
- * a fragment of C source code which defines the png_have_rvv function. There
- * are a number of implementations in contrib/riscv-rvv, but the only one that
- * has partial support is contrib/riscv-rvv/linux.c - a generic Linux
- * implementation which reads /proc/cpuinfo.
- */
-
 #include <signal.h>
 
 #ifndef PNG_RISCV_RVV_FILE
@@ -44,7 +30,6 @@ static int png_have_rvv(png_structp png_ptr);
 #ifdef PNG_RISCV_RVV_FILE
 #  include PNG_RISCV_RVV_FILE
 #endif
-#endif /* PNG_RISCV_RVV_CHECK_SUPPORTED */
 
 #ifndef PNG_ALIGNED_MEMORY_SUPPORTED
 #  error "ALIGNED_MEMORY is required; set: -DPNG_ALIGNED_MEMORY_SUPPORTED"
@@ -53,59 +38,16 @@ static int png_have_rvv(png_structp png_ptr);
 void
 png_init_filter_functions_rvv(png_structp pp, unsigned int bpp)
 {
-   /* The switch statement is compiled in for RISCV_RVV_API, the call to
-    * png_have_rvv is compiled in for RISCV_RVV_CHECK.  If both are
-    * defined the check is only performed if the API has not set the VECTOR
-    * option on or off explicitly.  In this case the check controls what
-    * happens.
-    */
    png_debug(1, "in png_init_filter_functions_rvv");
-#ifdef PNG_RISCV_RVV_API_SUPPORTED
-   switch ((pp->options >> PNG_RISCV_RVV) & 3)
-   {
-      case PNG_OPTION_UNSET:
-         /* Allow the run-time check to execute if it has been enabled -
-          * thus both API and CHECK can be turned on.  If it isn't supported
-          * this case will fall through to the 'default' below, which just
-          * returns.
-          */
-#endif /* PNG_RISCV_RVV_API_SUPPORTED */
-#ifdef PNG_RISCV_RVV_CHECK_SUPPORTED
-         {
-            static volatile sig_atomic_t no_rvv = -1; /* not checked */
 
-            if (no_rvv < 0)
+   static volatile sig_atomic_t no_rvv = -1; /* not checked */
-               no_rvv = !png_have_rvv(pp);
 
-            if (no_rvv)
+   if (no_rvv < 0)
-               return;
+      no_rvv = !png_have_rvv(pp);
-         }
-#ifdef PNG_RISCV_RVV_API_SUPPORTED
-         break;
-#endif
-#endif /* PNG_RISCV_RVV_CHECK_SUPPORTED */
 
-#ifdef PNG_RISCV_RVV_API_SUPPORTED
+   if (no_rvv)
-      default: /* OFF or INVALID */
+      return;
-         return;
 
-      case PNG_OPTION_ON:
-         /* Option turned on */
-         break;
-   }
-#endif /* PNG_RISCV_RVV_API_SUPPORTED */
-
-   /* IMPORTANT: any new external functions used here must be declared using
-    * PNG_INTERNAL_FUNCTION in ../pngpriv.h.  This is required so that the
-    * 'prefix' option to configure works:
-    *
-    *    ./configure --with-libpng-prefix=foobar_
-    *
-    * Verify you have got this right by running the above command, doing a build
-    * and examining pngprefix.h; it must contain a #define for every external
-    * function you add.  (Notice that this happens automatically for the
-    * initialization function.)
-    */
    pp->read_filter[PNG_FILTER_VALUE_UP-1] = png_read_filter_row_up_rvv;
 
    if (bpp == 3)