Index: gcc/fortran/trans-array.c
===================================================================
--- gcc/fortran/trans-array.c	(révision 117568)
+++ gcc/fortran/trans-array.c	(copie de travail)
@@ -3540,6 +3540,14 @@
             gfc_add_modify_expr (pblock, stride, tmp);
           else
             stride = gfc_evaluate_now (tmp, pblock);
+
+	  /* Make sure that negative size arrays are translated
+	     to being zero size.  */
+	  tmp = build2 (GE_EXPR, boolean_type_node,
+			stride, gfc_index_zero_node);
+	  tmp = build3 (COND_EXPR, gfc_array_index_type, tmp,
+			stride, gfc_index_zero_node);
+	  gfc_add_modify_expr (pblock, stride, tmp);
         }
 
       size = stride;
Index: gcc/fortran/ChangeLog
===================================================================
--- gcc/fortran/ChangeLog	(révision 117568)
+++ gcc/fortran/ChangeLog	(copie de travail)
@@ -1,3 +1,9 @@
+2006-10-16  Paul Thomas <pault@gcc.gnu.org>
+
+	PR fortran/20541
+	* trans-array.c (gfc_trans_array_bounds): Test for and set
+	negative stride of a non-constant bound array to zero.
+
 2006-10-08  Erik Edelmann <edelmann@gcc.gnu.org>
 	    Paul Thomas <pault@gcc.gnu.org>
 
Index: gcc/testsuite/ChangeLog
===================================================================
--- gcc/testsuite/ChangeLog	(révision 117568)
+++ gcc/testsuite/ChangeLog	(copie de travail)
@@ -1,3 +1,8 @@
+2006-10-16  Paul Thomas <pault@gcc.gnu.org>
+
+	PR fortran/20541
+	* gfortran.dg/negative_automatic_size.f90: New test.
+
 2006-10-08  Erik Edelmann  <edelmann@gcc.gnu.org>
 	    Paul Thomas  <pault@gcc.gnu.org>
 
Index: gcc/testsuite/gfortran.dg/negative_automatic_size.f90
===================================================================
--- gcc/testsuite/gfortran.dg/negative_automatic_size.f90	(révision 0)
+++ gcc/testsuite/gfortran.dg/negative_automatic_size.f90	(révision 0)
@@ -0,0 +1,28 @@
+! { dg-do run }
+! { dg-options "-O2" }
+! Tests the fix PR29451, in which the negative size of the
+! automatic array 'jello' was not detected and the
+! runtime error: Attempt to allocate a negative amount of memory
+! resulted.
+!
+! Contributed by Philip Mason  <pmason@ricardo.com> 
+!
+program fred
+  call jackal (1, 0)
+  call jackal (2, 1)
+  call jackal (3, 0)
+end
+
+subroutine jackal (b, c)
+  integer :: b, c
+  integer :: jello(b:c), cake(1:2, b:c), soda(b:c, 1:2)
+  if (lbound (jello, 1) <= ubound (jello, 1)) call abort ()
+  if (size (jello) /= 0) call abort ()
+
+  if (.not.any(lbound (cake) <= ubound (cake))) call abort ()
+  if (size (cake) /= 0) call abort ()
+
+  if (.not.any(lbound (soda) <= ubound (soda))) call abort ()
+  if (size (soda) /= 0) call abort ()
+
+end subroutine jackal