riscv: Fix the run-time checking of the RVV availability

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

CMakeLists.txt

@@ -323,7 +323,7 @@ if(PNG_HARDWARE_OPTIMIZATIONS)
     list(FIND PNG_RISCV_RVV_POSSIBLE_VALUES ${PNG_RISCV_RVV} index)
     if(index EQUAL -1)
       message(FATAL_ERROR "PNG_RISCV_RVV must be one of [${PNG_RISCV_RVV_POSSIBLE_VALUES}]")
-    elseif(NOT ${PNG_RISCV_RVV} STREQUAL "off")
+    elseif(NOT PNG_RISCV_RVV STREQUAL "off")
       check_c_compiler_flag("-march=rv64gv1p0" COMPILER_SUPPORTS_RVV)
       if(NOT COMPILER_SUPPORTS_RVV)
         message(FATAL_ERROR "Compiler does not support -march=rv64gv1p0 option")
@@ -331,9 +331,9 @@ if(PNG_HARDWARE_OPTIMIZATIONS)
       set(libpng_riscv_sources
           riscv/filter_rvv_intrinsics.c
           riscv/riscv_init.c)
-      if(${PNG_RISCV_RVV} STREQUAL "on")
+      if(PNG_RISCV_RVV STREQUAL "on")
         add_definitions(-DPNG_RISCV_RVV_OPT=2)
-      elseif(${PNG_RISCV_RVV} STREQUAL "check")
+      elseif(PNG_RISCV_RVV STREQUAL "check")
         add_definitions(-DPNG_RISCV_RVV_CHECK_SUPPORTED)
       endif()
     else()

contrib/riscv-rvv/linux.c

@@ -12,8 +12,8 @@
  * STATUS: SUPPORTED
  * BUG REPORTS: png-mng-implement@sourceforge.net
  *
- * png_have_rvv implemented for Linux by reading the widely available
+ * png_have_rvv implemented for Linux by looking for COMPAT_HWCAP_ISA_V
- * pseudo-file /proc/cpuinfo.
+ * via hardware capabilites API.
  *
  * This code is strict ANSI-C and is probably moderately portable; it does
  * however use <stdio.h> and it assumes that /proc/cpuinfo is never localized.

pngpriv.h

@@ -146,13 +146,19 @@
 #ifndef PNG_RISCV_RVV_OPT
    /* RISCV_RVV optimizations are being controlled by the compiler settings,
     * typically the target compiler will define __riscv but the rvv extension
-    * availability has to be explicitly stated
+    * availability has to be explicitly stated. This is why if no
+    * PNG_RISCV_RVV_OPT was defined then a runtime check will be executed.
     *
-    * To enable RISCV_RVV optimizations, and compile the
+    * To enable RISCV_RVV optimizations unconditionally, and compile the
     * associated code, pass --enable-riscv-rvv=yes or --enable-riscv-rvv=on
     * to configure or put -DPNG_RISCV_RVV_OPT=2 in CPPFLAGS.
     */
+
+#  if defined(__riscv) && defined(PNG_ALIGNED_MEMORY_SUPPORTED)
+#     define PNG_RISCV_RVV_OPT 1
+#  else
 #     define PNG_RISCV_RVV_OPT 0
+#  endif
 #endif
 
 #if PNG_ARM_NEON_OPT > 0

riscv/riscv_init.c

@@ -16,24 +16,22 @@
 
 #include <riscv_vector.h>
 
-#ifdef PNG_RISCV_RVV_CHECK_SUPPORTED
-#include <signal.h>
-#endif
-
 #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
+ * 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_neon function.  There
+ * 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
 #  if defined(__linux__)
 #    define PNG_RISCV_RVV_FILE "contrib/riscv-rvv/linux.c"