commit 2d7c83f52176a6ae1719fc43780e67499edd171d
author peter klausler <pklausler@nvidia.com> Tue Oct 12 10:17:02 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Tue Oct 12 16:05:30 2021 -0700
tree db57c3c584bf12d9e94bb0e82dbe0c1571fd9cfa
parent 878dc67767f64f47d79397fe80b6fdf4f9917a98

[flang][NFC] Document extension: scalars are trivially contiguous

The Fortran 2018 standard defines the concept of simple contiguity
in subclause 9.5.4 as a characteristic of arrays.  So that scalars
may also be used in contexts where simply contiguous arrays are
allowed, f18 treats them as single-element arrays that are trivially
contiguous.  This patch documents this semantic extension and
also adds comments to the predicate that implements the concept.

Differential Revision: https://reviews.llvm.org/D111679

GitOrigin-RevId: 6ee2aa126cf6bccb6a4af955a663ff3512aecc63

docs/Extensions.md

diff --git a/docs/Extensions.md b/docs/Extensions.md
index ac293ce..d4dacb7 100644
--- a/docs/Extensions.md
+++ b/docs/Extensions.md
@@ -175,6 +175,10 @@
 * OPEN(ACCESS='APPEND') is interpreted as OPEN(POSITION='APPEND')
   to ease porting from Sun Fortran.
 * Intrinsic subroutines EXIT([status]) and ABORT()
+* The definition of simple contiguity in 9.5.4 applies only to arrays;
+  we also treat scalars as being trivially contiguous, so that they
+  can be used in contexts like data targets in pointer assignments
+  with bounds remapping.
 
 ### Extensions supported when enabled by options
 

lib/Evaluate/check-expression.cpp

diff --git a/lib/Evaluate/check-expression.cpp b/lib/Evaluate/check-expression.cpp
index 2e0cc80..aaed4c3 100644
--- a/lib/Evaluate/check-expression.cpp
+++ b/lib/Evaluate/check-expression.cpp
@@ -626,8 +626,12 @@
 
   Result operator()(const semantics::Symbol &symbol) const {
     const auto &ultimate{symbol.GetUltimate()};
-    if (ultimate.attrs().test(semantics::Attr::CONTIGUOUS) ||
-        ultimate.Rank() == 0) {
+    if (ultimate.attrs().test(semantics::Attr::CONTIGUOUS)) {
+      return true;
+    } else if (ultimate.Rank() == 0) {
+      // Extension: accept scalars as a degenerate case of
+      // simple contiguity to allow their use in contexts like
+      // data targets in pointer assignments with remapping.
       return true;
     } else if (semantics::IsPointer(ultimate)) {
       return false;