Add configure test to see if the C compiler has gcc-style computed gotos.

We'll need this for the upcoming patch to speed up expression evaluation.
Might as well push it now to see if it behaves sanely in the buildfarm.

Andres Freund

Discussion: https://postgr.es/m/20170320062511.hp5qeurtxrwsvfxr@alap3.anarazel.de

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index 7d901e1f1aa20e15e24da00d6db5b8ebaa4c88a1..3321f226f3e4abd68d679e9a03b0b4fc18fe88e9 100644 (file)
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -273,6 +273,30 @@ fi])# PGAC_C_BUILTIN_UNREACHABLE
 
 
 
+# PGAC_C_COMPUTED_GOTO
+# -----------------------
+# Check if the C compiler knows computed gotos (gcc extension, also
+# available in at least clang).  If so, define HAVE_COMPUTED_GOTO.
+#
+# Checking whether computed gotos are supported syntax-wise ought to
+# be enough, as the syntax is otherwise illegal.
+AC_DEFUN([PGAC_C_COMPUTED_GOTO],
+[AC_CACHE_CHECK(for computed goto support, pgac_cv_computed_goto,
+[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([],
+[[void *labeladdrs[] = {&&my_label};
+  goto *labeladdrs[0];
+  my_label:
+  return 1;
+]])],
+[pgac_cv_computed_goto=yes],
+[pgac_cv_computed_goto=no])])
+if test x"$pgac_cv_computed_goto" = xyes ; then
+AC_DEFINE(HAVE_COMPUTED_GOTO, 1,
+          [Define to 1 if your compiler handles computed gotos.])
+fi])# PGAC_C_COMPUTED_GOTO
+
+
+
 # PGAC_C_VA_ARGS
 # --------------
 # Check if the C compiler understands C99-style variadic macros,

diff --git a/configure b/configure
index b5cdebb510b24dff22cc168a298cdf0a5db4f257..9528622421ed863e897e51f68ba9c212adc8cb41 100755 (executable)
--- a/configure
+++ b/configure
@@ -11531,6 +11531,40 @@ if test x"$pgac_cv__builtin_unreachable" = xyes ; then
 
 $as_echo "#define HAVE__BUILTIN_UNREACHABLE 1" >>confdefs.h
 
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for computed goto support" >&5
+$as_echo_n "checking for computed goto support... " >&6; }
+if ${pgac_cv_computed_goto+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+void *labeladdrs[] = {&&my_label};
+  goto *labeladdrs[0];
+  my_label:
+  return 1;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_computed_goto=yes
+else
+  pgac_cv_computed_goto=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_computed_goto" >&5
+$as_echo "$pgac_cv_computed_goto" >&6; }
+if test x"$pgac_cv_computed_goto" = xyes ; then
+
+$as_echo "#define HAVE_COMPUTED_GOTO 1" >>confdefs.h
+
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __VA_ARGS__" >&5
 $as_echo_n "checking for __VA_ARGS__... " >&6; }

diff --git a/configure.in b/configure.in
index 1d99cda1d8e502506ee934a922169c0f5817cbc5..7f234f543dae53ab975297e88cef077b8f99907f 100644 (file)
--- a/configure.in
+++ b/configure.in
@@ -1322,6 +1322,7 @@ PGAC_C_BUILTIN_BSWAP32
 PGAC_C_BUILTIN_BSWAP64
 PGAC_C_BUILTIN_CONSTANT_P
 PGAC_C_BUILTIN_UNREACHABLE
+PGAC_C_COMPUTED_GOTO
 PGAC_C_VA_ARGS
 PGAC_STRUCT_TIMEZONE
 PGAC_UNION_SEMUN

diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 5bcd8a1160fe580d10207ad3e6e93424b0e31fed..6a8176b323e38150a9598a453cd3a4179fef3420 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -108,6 +108,9 @@
 /* Define to 1 if you have the `clock_gettime' function. */
 #undef HAVE_CLOCK_GETTIME
 
+/* Define to 1 if your compiler handles computed gotos. */
+#undef HAVE_COMPUTED_GOTO
+
 /* Define to 1 if you have the <crtdefs.h> header file. */
 #undef HAVE_CRTDEFS_H
 

diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index 3e4132cd82406c3fbcfb7a7c52b00aa6795e9df6..5af8369202ca8e923e05ccd7d93abf7df7acd01d 100644 (file)
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -78,6 +78,9 @@
 /* Define to 1 if you have the `clock_gettime' function. */
 /* #undef HAVE_CLOCK_GETTIME */
 
+/* Define to 1 if your compiler handles computed gotos. */
+/* #undef HAVE_COMPUTED_GOTO */
+
 /* Define to 1 if you have the `crypt' function. */
 /* #undef HAVE_CRYPT */