Re: [PATCH] PR fortran/77505 -- Treat negative character length as LEN=0

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Wed, Nov 30, 2016 at 05:13:28AM +0000, Punnoose, Elizebeth wrote:
> Please excuse the messy formatting in my initial mail.  Resending
> with proper formatting.
> 
> This patch checks for negative character length in the array
> constructor, and treats it as LEN=0. 
> 
> A warning message is also printed if bounds checking is enabled.
> 
> Bootstrapped and regression tested the patch on x86_64-linux-gnu
> and aarch64-linux-gnu.
> 

Thanks.  After regression testing on x86_64-*-freebsd, I committed
the attached patch.  Not sure if the whitespace got messed up by 
my email agent, but I needed to reformat your testcases.  I took the
opportunity to rename and improve the testcases.  The improvements
check that in fact len=0 and that a warning is issued. 

Hopefully, you're inclined to submit additional patches in the future.
A few recommendations are to include the text of your ChangeLog 
entry in body of the email, for example,

2016-12-01  Elizebeth Punnoose  <elizebeth.punnoose@hpe.com>

	PR fortran/77505
	* trans-array.c (trans_array_constructor): Treat negative character
	length as LEN = 0.

2016-12-01  Elizebeth Punnoose  <elizebeth.punnoose@hpe.com>

	PR fortran/77505
	* gfortran.dg/char_length_20.f90: New test.
	* gfortran.dg/char_length_21.f90: Ditto.

(Note, 2 spaces before and after your name.)  Then attach the 
patch to the email.  This hopefully will prevent formatting
issues with various email clients/servers. 

-- 
Steve

Index: gcc/fortran/trans-array.c
===================================================================
--- gcc/fortran/trans-array.c	(revision 243134)
+++ gcc/fortran/trans-array.c	(working copy)
@@ -2226,6 +2226,8 @@ trans_array_constructor (gfc_ss * ss, lo
   gfc_ss_info *ss_info;
   gfc_expr *expr;
   gfc_ss *s;
+  tree neg_len;
+  char *msg;
 
   /* Save the old values for nested checking.  */
   old_first_len = first_len;
@@ -2271,6 +2273,29 @@ trans_array_constructor (gfc_ss * ss, lo
 	  gfc_conv_expr_type (&length_se, expr->ts.u.cl->length,
 			      gfc_charlen_type_node);
 	  ss_info->string_length = length_se.expr;
+
+	  /* Check if the character length is negative.  If it is, then
+	     set LEN = 0.  */
+	  neg_len = fold_build2_loc (input_location, LT_EXPR,
+				     boolean_type_node, ss_info->string_length,
+				     build_int_cst (gfc_charlen_type_node, 0));
+	  /* Print a warning if bounds checking is enabled.  */
+	  if (gfc_option.rtcheck & GFC_RTCHECK_BOUNDS)
+	    {
+	      msg = xasprintf ("Negative character length treated as LEN = 0");
+	      gfc_trans_runtime_check (false, true, neg_len, &length_se.pre,
+				       where, msg);
+	      free (msg);
+	    }
+
+	  ss_info->string_length
+	    = fold_build3_loc (input_location, COND_EXPR,
+			       gfc_charlen_type_node, neg_len,
+			       build_int_cst (gfc_charlen_type_node, 0),
+			       ss_info->string_length);
+	  ss_info->string_length = gfc_evaluate_now (ss_info->string_length,
+						     &length_se.pre);
+
 	  gfc_add_block_to_block (&outer_loop->pre, &length_se.pre);
 	  gfc_add_block_to_block (&outer_loop->post, &length_se.post);
 	}
Index: gcc/testsuite/gfortran.dg/char_length_20.f90
===================================================================
--- gcc/testsuite/gfortran.dg/char_length_20.f90	(nonexistent)
+++ gcc/testsuite/gfortran.dg/char_length_20.f90	(working copy)
@@ -0,0 +1,13 @@
+! { dg-do run }
+! { dg-options "-fcheck=bounds" }
+program rabbithole
+   implicit none
+   character(len=:), allocatable :: text_block(:)
+   integer i, ii
+   character(len=10) :: cten='abcdefghij'
+   character(len=20) :: ctwenty='abcdefghijabcdefghij'
+   ii = -6
+   text_block=[ character(len=ii) :: cten, ctwenty ]
+   if (any(len_trim(text_block) /= 0)) call abort
+end program rabbithole
+! { dg-output "At line 10 of file .*char_length_20.f90.*Fortran runtime warning: Negative character length treated as LEN = 0" }
Index: gcc/testsuite/gfortran.dg/char_length_21.f90
===================================================================
--- gcc/testsuite/gfortran.dg/char_length_21.f90	(nonexistent)
+++ gcc/testsuite/gfortran.dg/char_length_21.f90	(working copy)
@@ -0,0 +1,11 @@
+! { dg-do run }
+program rabbithole
+   implicit none
+   character(len=:), allocatable :: text_block(:)
+   integer i, ii
+   character(len=10) :: cten='abcdefghij'
+   character(len=20) :: ctwenty='abcdefghijabcdefghij'
+   ii = -6
+   text_block = [character(len=ii) :: cten, ctwenty]
+   if (any(len_trim(text_block) /= 0)) call abort
+end program rabbithole