[flang-commits] [flang] [flang][runtime] Fix finalization case in assignment (PR #113611)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/113611

There were two bugs in derived type array assignment processing that caused finalization to fail to occur for a test case. The first bug was an off-by-one error in address overlap testing that caused a false positive result for the test, whose left-hand side's allocatable's descriptor was immediately adjacent in memory to the right-hand side's array's data.
The second bug was that in such overlap cases (even when legitimate) finalization would fail due to the LHS's descriptor having been copied to a temporary for deferred deallocation and then nullified.

This patch corrects the overlap analysis for this test, and also properly finalizes the LHS when overlap does exist.  Some nearby dead code was removed to avoid future confusion.

Fixes https://github.com/llvm/llvm-project/issues/113375.

>From fbb11b79c9877ea6b59ac505c59dadb9062792d3 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Thu, 24 Oct 2024 12:13:03 -0700
Subject: [PATCH] [flang][runtime] Fix finalization case in assignment

There were two bugs in derived type array assignment processing
that caused finalization to fail to occur for a test case.
The first bug was an off-by-one error in address overlap testing
that caused a false positive result for the test, whose
left-hand side's allocatable's descriptor was immediately adjacent
in memory to the right-hand side's array's data.
The second bug was that in such overlap cases (even when legitimate)
finalization would fail due to the LHS's descriptor having been
copied to a temporary for deferred deallocation and then nullified.

This patch corrects the overlap analysis for this test, and also
properly finalizes the LHS when overlap does exist.  Some nearby
dead code was removed to avoid future confusion.

Fixes https://github.com/llvm/llvm-project/issues/113375.
---
 flang/runtime/assign.cpp | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/flang/runtime/assign.cpp b/flang/runtime/assign.cpp
index d558ada51cd21a..5c2ea2e4162834 100644
--- a/flang/runtime/assign.cpp
+++ b/flang/runtime/assign.cpp
@@ -155,9 +155,9 @@ static RT_API_ATTRS bool MayAlias(const Descriptor &x, const Descriptor &y) {
     return false; // not both allocated
   }
   const char *xDesc{reinterpret_cast<const char *>(&x)};
-  const char *xDescLast{xDesc + x.SizeInBytes()};
+  const char *xDescLast{xDesc + x.SizeInBytes() - 1};
   const char *yDesc{reinterpret_cast<const char *>(&y)};
-  const char *yDescLast{yDesc + y.SizeInBytes()};
+  const char *yDescLast{yDesc + y.SizeInBytes() - 1};
   std::int64_t xLeast, xMost, yLeast, yMost;
   MaximalByteOffsetRange(x, xLeast, xMost);
   MaximalByteOffsetRange(y, yLeast, yMost);
@@ -318,10 +318,8 @@ RT_API_ATTRS static void Assign(
     if (mustDeallocateLHS) {
       if (deferDeallocation) {
         if ((flags & NeedFinalization) && toDerived) {
-          Finalize(to, *toDerived, &terminator);
+          Finalize(*deferDeallocation, *toDerived, &terminator);
           flags &= ~NeedFinalization;
-        } else if (toDerived && !toDerived->noDestructionNeeded()) {
-          Destroy(to, /*finalize=*/false, *toDerived, &terminator);
         }
       } else {
         to.Destroy((flags & NeedFinalization) != 0, /*destroyPointers=*/false,