[gcc r12-2554] Bind(c): Fix bugs in CFI_section

[gcc r12-2554] Bind(c): Fix bugs in CFI_section

[Sandra Loosemore]

https://gcc.gnu.org/g:b4a9bc7856ee1d3ff98b04402334a362540af2cf

commit r12-2554-gb4a9bc7856ee1d3ff98b04402334a362540af2cf
Author: Sandra Loosemore <sandra@codesourcery.com>
Date:   Sat Jul 17 16:12:18 2021 -0700

    Bind(c): Fix bugs in CFI_section
    
    CFI_section was incorrectly adjusting the base pointer for the result
    array twice in different ways.  It was also overwriting the array
    dimension info in the result descriptor before computing the base
    address offset from the source descriptor, which caused problems if
    the two descriptors are the same.  This patch fixes both problems and
    makes the code simpler, too.
    
    A consequence of this patch is that the result array is now 0-based in
    all dimensions instead of starting at the numbering to match the first
    element of the source array.  The Fortran standard only specifies the
    shape of the result array, not its lower bounds, so this is permitted
    and probably less confusing for users as well as implementors.
    
    2021-07-17  Sandra Loosemore  <sandra@codesourcery.com>
    
            PR libfortran/101310
    
    libgfortran/
            * runtime/ISO_Fortran_binding.c (CFI_section): Fix the base
            address computation and simplify the code.
    
    gcc/testsuite/
            * gfortran.dg/ISO_Fortran_binding_1.c (section_c): Remove
            incorrect assertions.

Diff:
---
 gcc/testsuite/gfortran.dg/ISO_Fortran_binding_1.c | 10 +++++----
 libgfortran/runtime/ISO_Fortran_binding.c         | 27 +++++++++--------------
 2 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/gcc/testsuite/gfortran.dg/ISO_Fortran_binding_1.c b/gcc/testsuite/gfortran.dg/ISO_Fortran_binding_1.c
index 9da5d858806..bb56ca0e04b 100644
--- a/gcc/testsuite/gfortran.dg/ISO_Fortran_binding_1.c
+++ b/gcc/testsuite/gfortran.dg/ISO_Fortran_binding_1.c
@@ -142,11 +142,12 @@ float section_c(int *std_case, CFI_cdesc_t * source, int *low, int *str)
 			  CFI_type_float, 0, 1, NULL);
       if (ind) return -1.0;
       ind = CFI_section((CFI_cdesc_t *)&section, source, lower, NULL, strides);
-      assert (section.dim[0].lower_bound == lower[0]);
       if (ind) return -2.0;
 
       /* Sum over the section  */
-      for (idx[0] = lower[0]; idx[0] < section.dim[0].extent + lower[0]; idx[0]++)
+      for (idx[0] = section.dim[0].lower_bound;
+	   idx[0] < section.dim[0].extent + section.dim[0].lower_bound;
+	   idx[0]++)
         ans += *(float*)CFI_address ((CFI_cdesc_t*)&section, idx);
       return ans;
     }
@@ -164,11 +165,12 @@ float section_c(int *std_case, CFI_cdesc_t * source, int *low, int *str)
       ind = CFI_section((CFI_cdesc_t *)&section, source,
 			lower, upper, strides);
       assert (section.rank == 1);
-      assert (section.dim[0].lower_bound == lower[0]);
       if (ind) return -2.0;
 
       /* Sum over the section  */
-      for (idx[0] = lower[0]; idx[0] < section.dim[0].extent + lower[0]; idx[0]++)
+      for (idx[0] = section.dim[0].lower_bound;
+	   idx[0] < section.dim[0].extent + section.dim[0].lower_bound;
+	   idx[0]++)
         ans += *(float*)CFI_address ((CFI_cdesc_t*)&section, idx);
       return ans;
     }
diff --git a/libgfortran/runtime/ISO_Fortran_binding.c b/libgfortran/runtime/ISO_Fortran_binding.c
index b1e51612e2b..2830c4575fe 100644
--- a/libgfortran/runtime/ISO_Fortran_binding.c
+++ b/libgfortran/runtime/ISO_Fortran_binding.c
@@ -689,29 +689,22 @@ int CFI_section (CFI_cdesc_t *result, const CFI_cdesc_t *source,
 	}
     }
 
+  /* Set the base address.  We have to compute this first in the case
+     where source == result, before we overwrite the dimension data.  */
+  result->base_addr = CFI_address (source, lower);
+
   /* Set the appropriate dimension information that gives us access to the
    * data. */
-  int aux = 0;
-  for (int i = 0; i < source->rank; i++)
+  for (int i = 0, o = 0; i < source->rank; i++)
     {
       if (stride[i] == 0)
-	{
-	  aux++;
-	  /* Adjust 'lower' for the base address offset.  */
-	  lower[i] = lower[i] - source->dim[i].lower_bound;
-	  continue;
-	}
-      int idx = i - aux;
-      result->dim[idx].lower_bound = lower[i];
-      result->dim[idx].extent = 1 + (upper[i] - lower[i])/stride[i];
-      result->dim[idx].sm = stride[i] * source->dim[i].sm;
-      /* Adjust 'lower' for the base address offset.  */
-      lower[idx] = lower[idx] - source->dim[i].lower_bound;
+	continue;
+      result->dim[o].lower_bound = 0;
+      result->dim[o].extent = 1 + (upper[i] - lower[i])/stride[i];
+      result->dim[o].sm = stride[i] * source->dim[i].sm;
+      o++;
     }
 
-  /* Set the base address. */
-  result->base_addr = CFI_address (source, lower);
-
   return CFI_SUCCESS;
 }