ICC discarded qualifier warning for const pointer to array in generated C

[riftEmber]

Summary of Problem

Description: This issue documents a workaround in the compiler, of a known issue with const pointers in generated C code with ICC.

After https://github.com/chapel-lang/chapel/pull/24809 caused c_ptrConst to emit C const pointers in generated C, (only) Intel Compiler specific nightly tests using some parts of the Sort module began failing with the following error:

error #2332: a value of type "const void *" cannot be assigned to an entity of type "c_ptrConst__tuple_2_star_int64_t_chpl" (dropping qualifiers)

The offending line does a memcpy where the src is a c_ptrConst to an array element. When the c_ptrConst gets stored into a call tmp, the compiler warns of discarding the const qualifier. Technically we actually do discard a qualifier because the OS.POSIX.memcpy proc takes a const c_ptr, and I’m not sure why that isn’t warned elsewhere; however, changing that to a c_ptrConst does not make the problem go away. I dug into the generated C and found the call tmp has type c_ptrConst__tuple_2_star_int64_t_chpl (which implies we should be generating it as a const pointer). It’s defined by these chained typedefs:

• typedef const _tuple_2_star_int64_t_chpl *c_ptrConst__tuple_2_star_int64_t_chpl;
• typedef int64_t _tuple_2_star_int64_t_chpl[2]; My conclusion is that this doesn’t result in a const pointer to the Intel compiler (but does for GCC). My hunch is that’s due to first typedef in the chain getting decayed to a pointer immediately, which breaks as typedef const mutableptr constptr doesn’t give a const pointer but rather a pointer-to-const.

Manually changing to the following typedef works:

typedef const int64_t *c_ptrConst__tuple_2_star_int64_t_chpl

However I expect it would be pretty difficult to do programmatically. Additionally, changing the original offending line to use a mutable pointer instead also works, but we shouldn’t have to do that, and really it'd be losing information to do so.

We are going to work around this by adding a warning suppression flag to ICC for discarding qualifiers in generated C code, as the principled solution of changing the typedefs would be time consuming and specific to ICC. (PR https://github.com/chapel-lang/chapel/pull/24895)

Is this a blocking issue with no known work-arounds? Not blocking, this issue describes the workaround.

Steps to Reproduce

Source Code:

Test primer https://github.com/chapel-lang/chapel/blob/c5bc1fa172f934156c96624ed51fcfa751d1ed88/test/release/examples/primers/LinearAlgebralib.chpl

Compile command:

start_test test/release/examples/primers/LinearAlgebralib.chpl

Execution command: (also executed with start_test)

Associated Future Test(s): n/a

Configuration Information

• Output of chpl --version:

chpl version 2.1.0 pre-release (815d4be119)
Copyright 2020-2024 Hewlett Packard Enterprise Development LP
Copyright 2004-2019 Cray Inc.
(See LICENSE file for more details)

• Output of $CHPL_HOME/util/printchplenv --anonymize:

CHPL_TARGET_PLATFORM: cray-xc
CHPL_TARGET_COMPILER: cray-prgenv-intel
CHPL_TARGET_ARCH: x86_64
CHPL_TARGET_CPU: sandybridge
CHPL_LOCALE_MODEL: flat
CHPL_COMM: ugni
CHPL_TASKS: qthreads
CHPL_LAUNCHER: slurm-srun
CHPL_TIMERS: generic
CHPL_UNWIND: none
CHPL_MEM: jemalloc
CHPL_ATOMICS: intrinsics
  CHPL_NETWORK_ATOMICS: ugni
CHPL_GMP: bundled
CHPL_HWLOC: bundled
CHPL_RE2: bundled
CHPL_LLVM: none *
CHPL_AUX_FILESYS: none

• Back-end compiler and version, e.g. gcc --version or clang --version:

gcc (SUSE Linux) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

icc: remark #10441: The Intel(R) C++ Compiler Classic (ICC) is deprecated and will be removed from product release in the second half of 2023. The Intel(R) oneAPI DPC++/C++ Compiler (ICX) is the recommended compiler moving forward. Please transition to use this compiler. Use '-diag-disable=10441' to disable this message.
icc (ICC) 2021.7.0 20220726
Copyright (C) 1985-2022 Intel Corporation.  All rights reserved.

• (For Cray systems only) Output of module list:

Currently Loaded Modules:
  1) slurm/20.11.5-1                                3) craype/2.7.21.6   5) PrgEnv-intel/6.0.10      7) cray-libsci/22.05.1   9) craype-sandybridge
  2) Base-opts/2.4.142-7.0.4.0_43.5__g8f27585.ari   4) pmi/5.0.17.1      6) intel-classic/2022.2.0   8) craype-network-none  10) cray-fftw/3.3.8.13