GCC-specific optimization hints not guarded against Clang and partially not guarded against IAR, causing compiler warnings

[Symanyshyn-IFX]

Several source files in CMSIS-NN use GCC-specific optimization hints that are not properly guarded against non-GCC compilers. Building with Clang/LLVM Embedded Toolchain for Arm produces warnings, and one case also affects IAR.

Case 1 - attribute((optimize(...))) missing Clang and IAR guards

CMSIS-NN/Source/ConvolutionFunctions/arm_depthwise_conv_s8.c

Line 43 in 22080c6

#if !defined(__ARMCC_VERSION)

Problem:
The guard only excludes Arm Compiler (__ARMCC_VERSION). Clang
(clang) and IAR (ICCARM) are not excluded, so both compilers
receive the GCC-specific attribute.

Compilers affected:

• Clang/LLVM Embedded Toolchain for Arm 19.1.5 - warning:

  warning: unknown attribute 'optimize' ignored [-Wunknown-attributes]
  

• IAR C/C++ Compiler for Arm 9.70.1 - warning:

  Warning[Pe1097]: unknown attribute 'optimize'
  

Suggested fix:

#if !defined(__ARMCC_VERSION) && !defined(__ICCARM__) && !defined(__clang__)
__attribute__((optimize("no-unroll-loops")))
#endif

Case 2 - #pragma GCC optimize(...) missing Clang guard

Files:

CMSIS-NN/Source/NNSupportFunctions/arm_nn_vec_mat_mult_t_s8.c

Line 55 in 22080c6

#if !defined(ARM_MATH_MVEI) && defined(ARM_MATH_DSP) && !defined(__ARMCC_VERSION) && !defined(__ICCARM__)

CMSIS-NN/Source/NNSupportFunctions/arm_nn_vec_mat_mult_t_per_ch_s8.c

Line 55 in 22080c6

#if !defined(ARM_MATH_MVEI) && defined(ARM_MATH_DSP) && !defined(__ARMCC_VERSION) && !defined(__ICCARM__)

Problem:
The guard correctly excludes ARMCC and IAR, but does not exclude Clang,
which does not implement #pragma GCC optimize.

Compilers affected:

• Clang/LLVM Embedded Toolchain for Arm 19.1.5 - warning:

  warning: unknown pragma ignored [-Wunknown-pragmas]
  

Suggested fix:

#if !defined(ARM_MATH_MVEI) && defined(ARM_MATH_DSP) && !defined(__ARMCC_VERSION) && !defined(__ICCARM__) && !defined(__clang__)
    #pragma GCC optimize("unroll-loops")
#endif

Environment

• Toolchain: LLVM Embedded Toolchain for Arm 19.1.5, IAR C/C++ Compiler for Arm: 9.70.1
• Target: Cortex-M33, Cortex-M55

[mansnils]

Thanks you @Symanyshyn-IFX
Note that currently, CMSIS-NN only claims official support for armclang (Arm Compiler) and GCC: https://github.com/ARM-software/CMSIS-NN/blob/22080c68d040c98139e6cb1549473e3149735f4d/Include/Internal/arm_nn_compiler.h
That being said, your fix suggestions look good.