* inline.h (scm_double_cell): prevent reordering of statements

with any following code (for GCC 3 strict-aliasing).
	* numbers.c (scm_make_real), num2float.i.c (FLOAT2NUM): removed
	the earlier version of the reordering prevention.

libguile/ChangeLog

@@ -1,3 +1,10 @@
+2002-09-24  Gary Houston  <ghouston@arglist.com>
+
+	* inline.h (scm_double_cell): prevent reordering of statements
+	with any following code (for GCC 3 strict-aliasing).
+	* numbers.c (scm_make_real), num2float.i.c (FLOAT2NUM): removed
+	the earlier version of the reordering prevention.
+
 2002-09-19  Han-Wen Nienhuys  <hanwen@cs.uu.nl>
 
 	* inline.h (scm_double_cell): move SET_GCMARK set out of if body. 

libguile/inline.h

@@ -213,6 +213,26 @@ scm_double_cell (scm_t_bits car, scm_t_bits cbr,
   /* see above. */
   SCM_SET_GC_MARK (z);
 
+#endif
+
+  /* When this function is inlined, it's possible that the last
+     SCM_GC_SET_CELL_WORD above will be adjacent to a following
+     initialization of z.  E.g., it occurred in scm_make_real.  GCC
+     from around version 3 (e.g., certainly 3.2) began taking
+     advantage of strict C aliasing rules which say that it's OK to
+     interchange the initialization above and the one below when the
+     pointer types appear to differ sufficiently.  We don't want that,
+     of course.  GCC allows this behaviour to be disabled with the
+     -fno-strict-aliasing option, but would also need to be supplied
+     by Guile users.  Instead, the following statements prevent the
+     reordering.
+   */
+#ifdef __GNUC__
+  asm volatile ("" : : : "memory");
+#else
+  /* portable version, just in case any other compiler does the same
+     thing.  */
+  scm_remember_upto_here_1 (z);
 #endif
 
   return z;

libguile/num2float.i.c

@@ -31,12 +31,8 @@ NUM2FLOAT (SCM num, unsigned long int pos, const char *s_caller)
 SCM
 FLOAT2NUM (FTYPE n)
 {
-  SCM z;
+  SCM z = scm_double_cell (scm_tc16_real, 0, 0, 0);
-  z = scm_double_cell (scm_tc16_real, 0, 0, 0);
+
-  /*
-    See scm_make_real().
-   */
-  scm_remember_upto_here_1 (z);
   SCM_REAL_VALUE (z) = n;
   return z;
 }

libguile/numbers.c

@@ -3013,15 +3013,8 @@ SCM_DEFINE (scm_string_to_number, "string->number", 1, 1, 0,
 SCM
 scm_make_real (double x)
 {
-  SCM z;
+  SCM z = scm_double_cell (scm_tc16_real, 0, 0, 0);
-  z = scm_double_cell (scm_tc16_real, 0, 0, 0);
 
-  /*
-    scm_double_cell is inlined. strict C aliasing rules say that it's
-    OK to interchange the initialization above and the one below. We
-    don't want that, of course.
-   */
-  scm_remember_upto_here_1 (z);
   SCM_REAL_VALUE (z) = x;
   return z;
 }