[flang-commits] [flang] bef3e8e - [flang][runtime] Fix another IsContiguous edge case (#69199)

[via flang-commits]

Author: jeanPerier
Date: 2023-10-17T08:49:43+02:00
New Revision: bef3e8ea6d241a7e249410e85cff36cddfa98720

URL: https://github.com/llvm/llvm-project/commit/bef3e8ea6d241a7e249410e85cff36cddfa98720
DIFF: https://github.com/llvm/llvm-project/commit/bef3e8ea6d241a7e249410e85cff36cddfa98720.diff

LOG: [flang][runtime] Fix another IsContiguous edge case (#69199)

A recent PR addressed zero and one element edge cases but did not cover
another case where the descriptors of arrays with more than two elements
may have byte strides that are not perfect multiples, like when creating
a descriptor for A(:, 1:1:2).

In general, the byte stride in a dimension is only meaningful if that
dimension has more than one element. Update IsContiguous and
CFI_is_contiguous to reflect that.

Added: 
    

Modified: 
    flang/include/flang/Runtime/descriptor.h
    flang/runtime/ISO_Fortran_binding.cpp
    flang/unittests/Evaluate/ISO-Fortran-binding.cpp

Removed: 
    


################################################################################
diff  --git a/flang/include/flang/Runtime/descriptor.h b/flang/include/flang/Runtime/descriptor.h
index c69bb336dd29e7d..85240353e8ae9e0 100644
--- a/flang/include/flang/Runtime/descriptor.h
+++ b/flang/include/flang/Runtime/descriptor.h
@@ -393,13 +393,17 @@ class Descriptor {
     bool stridesAreContiguous{true};
     for (int j{0}; j < leadingDimensions; ++j) {
       const Dimension &dim{GetDimension(j)};
-      stridesAreContiguous &= bytes == dim.ByteStride();
+      stridesAreContiguous &= (bytes == dim.ByteStride()) | (dim.Extent() == 1);
       bytes *= dim.Extent();
     }
     // One and zero element arrays are contiguous even if the descriptor
     // byte strides are not perfect multiples.
-    return stridesAreContiguous || bytes == 0 ||
-        bytes == static_cast<SubscriptValue>(ElementBytes());
+    // Arrays with more than 2 elements may also be contiguous even if a
+    // byte stride in one dimension is not a perfect multiple, as long as
+    // this is the last dimension, or if the dimension has one extent and
+    // the following dimension have either one extents or contiguous byte
+    // strides.
+    return stridesAreContiguous || bytes == 0;
   }
 
   // Establishes a pointer to a section or element.

diff  --git a/flang/runtime/ISO_Fortran_binding.cpp b/flang/runtime/ISO_Fortran_binding.cpp
index 103413cb7140aaa..c2e82758ae08aef 100644
--- a/flang/runtime/ISO_Fortran_binding.cpp
+++ b/flang/runtime/ISO_Fortran_binding.cpp
@@ -125,16 +125,15 @@ RT_API_ATTRS int CFI_establish(CFI_cdesc_t *descriptor, void *base_addr,
 }
 
 RT_API_ATTRS int CFI_is_contiguous(const CFI_cdesc_t *descriptor) {
+  // See Descriptor::IsContiguous for the rationale.
   bool stridesAreContiguous{true};
   CFI_index_t bytes = descriptor->elem_len;
   for (int j{0}; j < descriptor->rank; ++j) {
-    stridesAreContiguous &= bytes == descriptor->dim[j].sm;
+    stridesAreContiguous &=
+        (bytes == descriptor->dim[j].sm) | (descriptor->dim[j].extent == 1);
     bytes *= descriptor->dim[j].extent;
   }
-  // One and zero element arrays are contiguous even if the descriptor
-  // byte strides are not perfect multiples.
-  if (stridesAreContiguous || bytes == 0 ||
-      bytes == static_cast<CFI_index_t>(descriptor->elem_len)) {
+  if (stridesAreContiguous || bytes == 0) {
     return 1;
   }
   return 0;

diff  --git a/flang/unittests/Evaluate/ISO-Fortran-binding.cpp b/flang/unittests/Evaluate/ISO-Fortran-binding.cpp
index d1f0a31454056bf..3c98363f9004664 100644
--- a/flang/unittests/Evaluate/ISO-Fortran-binding.cpp
+++ b/flang/unittests/Evaluate/ISO-Fortran-binding.cpp
@@ -736,6 +736,38 @@ static void run_CFI_is_contiguous_tests() {
   MATCH(true, retCode == CFI_SUCCESS);
   MATCH(true, CFI_is_contiguous(section) == 0);
   MATCH(false, sectionDesc->IsContiguous());
+
+  // Test section B = A(0:3:1,0:0:2) is contiguous.
+  lb[0] = 0;
+  lb[1] = 0;
+  ub[0] = 3;
+  ub[1] = 0;
+  strides[0] = 1;
+  strides[1] = 2;
+  retCode = CFI_section(section, dv, lb, ub, strides);
+  MATCH(true, retCode == CFI_SUCCESS);
+  MATCH(true, CFI_is_contiguous(section) == 1);
+  MATCH(true, sectionDesc->IsContiguous());
+
+  // INTEGER :: C(0:0, 0:3)
+  CFI_index_t c_extents[rank] = {1, 4};
+  CFI_CDESC_T(rank) c_dv_storage;
+  CFI_cdesc_t *cdv{&c_dv_storage};
+  retCode = CFI_establish(cdv, base_addr, CFI_attribute_other, CFI_type_int,
+      /*elem_len=*/0, rank, c_extents);
+  MATCH(retCode == CFI_SUCCESS, true);
+
+  // Test section B = C(0:0:2, 0:3:1) is contiguous.
+  lb[0] = 0;
+  lb[1] = 0;
+  ub[0] = 0;
+  ub[1] = 3;
+  strides[0] = 2;
+  strides[1] = 1;
+  retCode = CFI_section(section, cdv, lb, ub, strides);
+  MATCH(true, retCode == CFI_SUCCESS);
+  MATCH(true, CFI_is_contiguous(section) == 1);
+  MATCH(true, sectionDesc->IsContiguous());
 }
 
 int main() {