nan-boxing: use GCC pragmas to disable aliasing warnings.

* arith.c (flo): The line of code which triggers the
aliasing diagnostic is wrapped with GNU-C-specific
pramgas that disable the diagnostic just for that line.

* lib.h (c_f): Likewise.

* configure: Drop the test which adds -Wno-strict-aliasing
to the DIAG_FLAGS;

3 files changed, 14 insertions, 18 deletions

diff --git a/arith.c b/arith.c
index 30847a4a..d135e2a4 100644
--- a/arith.c
+++ b/arith.c
@@ -4274,7 +4274,14 @@ val flo(double n)
     uw_throw(numeric_error_s, lit("out-of-range floating-point result"));
   } else {
 #if CONFIG_NAN_BOXING
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
+#endif
     ucnum u = *(ucnum *) &n + NAN_FLNUM_DELTA;
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
     return coerce(val, u);
 #else
     val obj = make_obj();
diff --git a/configure b/configure
index 01ac4531..51c11fa8 100755
--- a/configure
+++ b/configure
@@ -1603,24 +1603,6 @@ if [ -n "$nan_boxing" ] ; then
   fi
 fi
 
-if [ -n "$nan_boxing" ] ; then
-  printf "Checking how to disable strict aliasing warnings ... "
-
-  cat > conftest.c <<!
-int main(void)
-{
-  return 0;
-}
-!
-
-  if conftest EXTRA_FLAGS=-Wno-strict-aliasing ; then
-    printf -- "-Wno-strict-aliasing\n"
-    diag_flags="$diag_flags -Wno-strict-aliasing"
-  else
-    printf "unknown\n"
-  fi
-fi
-
 printf "Checking for intmax_t  ... "
 cat > conftest.c <<!
 #include <inttypes.h>
diff --git a/lib.h b/lib.h
index 35a237fa..c2f42408 100644
--- a/lib.h
+++ b/lib.h
@@ -625,7 +625,14 @@ INLINE double c_f(val num)
 {
 #if CONFIG_NAN_BOXING
   ucnum u = coerce(ucnum, num) - NAN_FLNUM_DELTA;
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
+#endif
   return *coerce(double *, &u);
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
 #else
   return num->fl.n;
 #endif