Add --enable-jit=auto support.

ChangeLog

@@ -30,6 +30,8 @@ read from files via the -f option.
 
 6. A small fix to pcre2grep to avoid compiler warnings for -Wformat-overflow=2.
 
+7. Added --enable-jit=auto support to configure.ac.
+
 
 Version 10.31 12-February-2018
 ------------------------------

README

@@ -171,10 +171,12 @@ library. They are also documented in the pcre2build man page.
   give large performance improvements on certain platforms, add --enable-jit to
   the "configure" command. This support is available only for certain hardware
   architectures. If you try to enable it on an unsupported architecture, there
-  will be a compile time error. If you are running under SELinux you may also
-  want to add --enable-jit-sealloc, which enables the use of an execmem
-  allocator in JIT that is compatible with SELinux. This has no effect if JIT
-  is not enabled.
+  will be a compile time error. If in doubt, use --enable-jit=auto, which
+  enables JIT only if the current hardware is supported.
+
+. If you are enabling JIT under SELinux you may also want to add
+  --enable-jit-sealloc, which enables the use of an execmem allocator in JIT
+  that is compatible with SELinux. This has no effect if JIT is not enabled.
 
 . If you do not want to make use of the default support for UTF-8 Unicode
   character strings in the 8-bit library, UTF-16 Unicode character strings in
@@ -883,4 +885,4 @@ The distribution should contain the files listed below.
 Philip Hazel
 Email local part: ph10
 Email domain: cam.ac.uk
-Last updated: 12 September 2017
+Last updated: 25 February 2018

configure.ac

@@ -142,6 +142,18 @@ AC_ARG_ENABLE(jit,
               AS_HELP_STRING([--enable-jit],
                              [enable Just-In-Time compiling support]),
               , enable_jit=no)
+              
+# This code enables JIT if the hardware supports it.
+if test "$enable_jit" = "auto"; then
+  AC_LANG(C)
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+  #define SLJIT_CONFIG_AUTO 1
+  #include "src/sljit/sljitConfigInternal.h"
+  #if (defined SLJIT_CONFIG_UNSUPPORTED && SLJIT_CONFIG_UNSUPPORTED)
+  #error unsupported
+  #endif]])], enable_jit=yes, enable_jit=no)
+  echo checking for JIT support on this hardware... $enable_jit
+fi
 
 # Handle --enable-jit-sealloc (disabled by default)
 AC_ARG_ENABLE(jit-sealloc,

doc/pcre2build.3

@@ -1,4 +1,4 @@
-.TH PCRE2BUILD 3 "18 July 2017" "PCRE2 10.30"
+.TH PCRE2BUILD 3 "25 February 2018" "PCRE2 10.32"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .
@@ -59,7 +59,8 @@ The following sections include descriptions of "on/off" options whose names
 begin with --enable or --disable. Because of the way that \fBconfigure\fP
 works, --enable and --disable always come in pairs, so the complementary option
 always exists as well, but as it specifies the default, it is not described.
-Options that specify values have names that start with --with.
+Options that specify values have names that start with --with. At the end of a 
+\fBconfigure\fP run, a summary of the configuration is output.
 .
 .
 .SH "BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES"
@@ -156,8 +157,15 @@ Just-in-time (JIT) compiler support is included in the build by specifying
   --enable-jit
 .sp
 This support is available only for certain hardware architectures. If this
-option is set for an unsupported architecture, a building error occurs. If you
-are running under SELinux you may also want to add
+option is set for an unsupported architecture, a building error occurs. 
+If in doubt, use 
+.sp
+  --enable-jit=auto
+.sp
+which enables JIT only if the current hardware is supported. You can check 
+if JIT is enabled in the configuration summary that is output at the end of a
+\fBconfigure\fP run. If you are enabling JIT under SELinux you may also want to
+add
 .sp
   --enable-jit-sealloc
 .sp
@@ -582,6 +590,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 18 July 2017
-Copyright (c) 1997-2017 University of Cambridge.
+Last updated: 25 February 2018
+Copyright (c) 1997-2018 University of Cambridge.
 .fi