[llvm] [flang-rt] Optimise ShallowCopy and use it in CopyInAssign (PR #140569)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64-flang-aix` running on `ppc64-flang-aix-test` while building `flang-rt` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/201/builds/4736

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (build-unified-tree) failure: build (failure)
...
      |           ^~~~
1 warning generated.
4.554 [2/82/89] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/array-constructor.cpp.o
4.555 [2/81/90] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_environment.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
4.556 [2/80/91] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_utility.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
4.579 [2/79/92] Generating /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/build/compile_commands.json
4.611 [2/78/93] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/derived-api.cpp.o
4.672 [2/77/94] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/assign.cpp.o
FAILED: flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/assign.cpp.o 
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/build/./bin/clang++ --target=powerpc64-ibm-aix -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LARGE_FILE_API -D_XOPEN_SOURCE=700 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/flang-rt/include -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/flang-rt/../flang/include -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/build/runtimes/runtimes-bins/flang-rt -mcmodel=large -fPIC -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wno-unnecessary-virtual-specifier -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=gnu++17 -UNDEBUG -fno-lto -fno-exceptions -fno-rtti -funwind-tables -fno-asynchronous-unwind-tables -U_GLIBCXX_ASSERTIONS -U_LIBCPP_ENABLE_ASSERTIONS -MD -MT flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/assign.cpp.o -MF flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/assign.cpp.o.d -o flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/assign.cpp.o -c /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/flang-rt/lib/runtime/assign.cpp
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/flang-rt/lib/runtime/assign.cpp:594:17: error: use of undeclared identifier 'kNoAsyncId'
  594 |   temp.Allocate(kNoAsyncId);
      |                 ^~~~~~~~~~
1 error generated.
4.722 [2/76/95] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/memory.cpp.o
4.723 [2/75/96] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_error.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
4.857 [2/74/97] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/support.cpp.o
4.937 [2/73/98] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/ISO_Fortran_binding.cpp.o
5.032 [2/72/99] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_wait_release.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
5.248 [2/71/100] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_threadprivate.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
5.457 [2/70/101] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/connection.cpp.o
5.488 [2/69/102] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/copy.cpp.o
5.505 [2/68/103] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_str.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
5.519 [2/67/104] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_sched.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
5.616 [2/66/105] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_ftn_extra.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
In file included from /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/openmp/runtime/src/kmp_ftn_extra.cpp:14:
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/openmp/runtime/src/kmp_affinity.h:447:11: warning: unused variable 'gtid' [-Wunused-variable]
  447 |       int gtid = __kmp_entry_gtid();
      |           ^~~~
1 warning generated.
5.646 [2/65/106] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_ftn_cdecl.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
In file included from /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/openmp/runtime/src/kmp_ftn_cdecl.cpp:14:
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/openmp/runtime/src/kmp_affinity.h:447:11: warning: unused variable 'gtid' [-Wunused-variable]
  447 |       int gtid = __kmp_entry_gtid();
      |           ^~~~
1 warning generated.
6.138 [2/64/107] Building CXX object openmp/runtime/src/CMakeFiles/omp.dir/kmp_taskdeps.cpp.o
clang++: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
6.346 [2/63/108] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/misc-intrinsic.cpp.o
6.348 [2/62/109] Building CXX object flang-rt/lib/runtime/CMakeFiles/flang_rt.runtime.static.dir/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/flang/lib/Decimal/decimal-to-binary.cpp.o

```

</details>

https://github.com/llvm/llvm-project/pull/140569