Solaris2 trunk failure w/C_alloca in gencodes

["Kaveh R. Ghazi" <ghazi at caip dot rutgers dot edu>]

 > 2001-06-16  Daniel Berlin  <dan@cgsoftware.com>
 > 
 >      * bitmap.h: Add dump_bitmap, bitmap_zero, bitmap_union_of_diffs,
 >      bitmap_a_or_b, bitmap_a_and_b, bitmap_first_set_bit,
 >      bitmap_last_set_bit. All for compatibility with sbitmap's.
 > 
 >      *bitmap.c (bitmap_zero): New function.
 >      (bitmap_union_of_diffs): New function.
 >      (bitmap_first_set_bit): New function.
 >      (bitmap_last_set_bit): New function.

The above patch breaks the trunk on solaris2 (and probably others)
when using cc for stage1.  (E.g. David noted it on irix6.5.)  Here's
the failure:

 > cc -DIN_GCC -g -DHAVE_CONFIG_H -DGENERATOR_FILE -o gencodes \
 >  gencodes.o rtl.o bitmap.o ggc-none.o gensupport.o hashtab.o
 >  safe-ctype.o print-rtl.o errors.o ` case "obstack.o" in ?*) echo
 >  obstack.o ;; esac ` ` case "" in ?*) echo ;; esac ` ` case "" in ?*)
 >  echo ;; esac ` ` case "" in ?*) echo ;; esac `
 > ild: (undefined symbol) C_alloca -- referenced in the text segment of
 >      bitmap.o
 > make.solaris2[2]: *** [gencodes] Error 5

There are two problems.

First, the patch uses alloca in bitmap.c.  Any file like bitmap.c
which is used on both host and build platforms cannot use alloca since
we don't link against libiberty for "build" programs to obtain
C_alloca().  That's the cause of the failure above.

The second, more insidious, problem is this definition from bitmap.h:

 > /* Allocate a bitmap with alloca.  */
 > #define BITMAP_ALLOCA()                                         \
 >   bitmap_initialize ((bitmap) alloca (sizeof (bitmap_head)))

IIRC, passing alloca as an argument of a function is not guaranteed to
work in all cases on all platforms, even when only using gcc.  Mixing
in other stage1 compiler's alloca implementations is only worse.

(Side note: I wish gcc would warn whenever someone does this.  Maybe
something for the "projects" list.)

Anyway, I don't think the definition of BITMAP_ALLOCA came from Dan's
patch, but using it did.  We should change bitmap_union_of_diff() so
that it doesn't use alloca, *and* we should change BITMAP_ALLOCA so
that it doesn't pass alloca as a function argument.  Note Dan's usage
of BITMAP_ALLOCA was the only one appearing in gcc sources at the
moment.


Here's an untested patch which does this.  Unfortunately solaris2
doesn't bootstrap on the trunk for other reasons at the moment noted
here: http://gcc.gnu.org/ml/gcc-bugs/2001-06/msg00842.html

Also I'll be away for a week starting Monday, so I won't be able to
test and/or checkin this patch until the following weekend at the
earliest (if the other solaris2 problem is fixed by then.)  If someone
else (Dan?) could spin this on something other than solaris2 and check
it in when approved I'd appreciate it.

		Thanks,
		--Kaveh


2001-06-17  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>

	* bitmap.c (bitmap_union_of_diff): Don't use BITMAP_ALLOCA.

	* bitmap.h (BITMAP_ALLOCA): Don't pass alloca as an argument to a
	function.

diff -rup orig/egcs-CVS20010617/gcc/bitmap.c egcs-CVS20010617/gcc/bitmap.c
--- orig/egcs-CVS20010617/gcc/bitmap.c	Sat Jun 16 16:30:14 2001
+++ egcs-CVS20010617/gcc/bitmap.c	Sun Jun 17 22:11:56 2001
@@ -687,9 +687,11 @@ bitmap_union_of_diff (dst, a, b, c)
      bitmap c;
 {
   int changed = 0;
-  bitmap temp = BITMAP_ALLOCA ();
+  bitmap temp = BITMAP_XMALLOC ();
+  
   bitmap_operation (temp, b, c, BITMAP_AND_COMPL);
   changed = bitmap_operation (dst, temp, a, BITMAP_IOR);
+  BITMAP_XFREE (temp);
   return changed;
 }
 
diff -rup orig/egcs-CVS20010617/gcc/bitmap.h egcs-CVS20010617/gcc/bitmap.h
--- orig/egcs-CVS20010617/gcc/bitmap.h	Sat Jun 16 16:30:14 2001
+++ egcs-CVS20010617/gcc/bitmap.h	Sun Jun 17 22:09:50 2001
@@ -119,10 +119,17 @@ extern int bitmap_last_set_bit PARAMS((b
 #define BITMAP_OBSTACK_ALLOC(OBSTACK)				\
   bitmap_initialize ((bitmap) obstack_alloc (OBSTACK, sizeof (bitmap_head)))
 
-/* Allocate a bitmap with alloca.  */
-#define BITMAP_ALLOCA()						\
-  bitmap_initialize ((bitmap) alloca (sizeof (bitmap_head)))
-
+/* Allocate a bitmap with alloca.  Note alloca cannot be passed as an
+   argument to a function, so we set a temporary variable to the value
+   returned by alloca and pass that variable to bitmap_initialize().
+   PTR is then set to the value returned from bitmap_initialize() to
+   avoid having it appear more than once in case it has side effects.  */
+#define BITMAP_ALLOCA(PTR) \
+do { \
+  bitmap temp_bitmap_ = (bitmap) alloca (sizeof (bitmap_head)); \
+  (PTR) = bitmap_initialize (temp_bitmap_); \
+} while (0)
+  
 /* Allocate a bitmap with xmalloc.  */
 #define BITMAP_XMALLOC()                                        \
   bitmap_initialize ((bitmap) xmalloc (sizeof (bitmap_head)))