Re: lib/eal/arm/include/rte_vect.h fails to compile with clang14 for 32bit ARM

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

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+Arm folks.

From: Roger Melton (rmelton) <rmelton@cisco.com>
Date: Tuesday, December 3, 2024 at 3:39 AM
To: dev@dpdk.org <dev@dpdk.org>, Ruifeng Wang <Ruifeng.Wang@arm.com>
Subject: lib/eal/arm/include/rte_vect.h fails to compile with clang14 for 32bit ARM

Hey folks,
We are building DPDK with clang14 for a 32bit armv8-a based CPU and ran into a compile error with the following from lib/eal/arm/include/rte_vect.h:



#if (defined(RTE_ARCH_ARM) && defined(RTE_ARCH_32)) || \

(defined(RTE_ARCH_ARM64) && RTE_CC_IS_GNU<https://elixir.bootlin.com/dpdk/v24.11/C/ident/RTE_CC_IS_GNU> && (GCC_VERSION<https://elixir.bootlin.com/dpdk/v24.11/C/ident/GCC_VERSION> < 70000))

/* NEON intrinsic vcopyq_laneq_u32() is not supported in ARMv7-A(AArch32)

 * On AArch64, this intrinsic is supported since GCC version 7.

 */

static inline uint32x4_t

vcopyq_laneq_u32<https://elixir.bootlin.com/dpdk/v24.11/C/ident/vcopyq_laneq_u32>(uint32x4_t a, const int lane_a,

          uint32x4_t b, const int lane_b)

{

  return vsetq_lane_u32(vgetq_lane_u32(b, lane_b), a, lane_a);

}

#endif

clang14 compile fails as follows:

In file included from ../../../../../../cisco-dpdk-upstream-arm-clang-fixes.git/lib/eal/common/eal_common_options.c:36:
../../../../../../cisco-dpdk-upstream-arm-clang-fixes.git/lib/eal/arm/include/rte_vect.h:80:24: error: argument to '__builtin_neon_vgetq_lane_i32' must be a constant integer
return vsetq_lane_u32(vgetq_lane_u32(b, lane_b), a, lane_a);
^ ~~~~~~
/auto/binos-tools/llvm14/llvm-14.0-p24/lib/clang/14.0.5/include/arm_neon.h:7697:22: note: expanded from macro 'vgetq_lane_u32'
__ret = (uint32_t) __builtin_neon_vgetq_lane_i32((int32x4_t)__s0, __p1); \
^ ~~~~
/auto/binos-tools/llvm14/llvm-14.0-p24/lib/clang/14.0.5/include/arm_neon.h:24148:19: note: expanded from macro 'vsetq_lane_u32'
uint32_t __s0 = __p0; \
^~~~
In file included from ../../../../../../cisco-dpdk-upstream-arm-clang-fixes.git/lib/eal/common/eal_common_options.c:36:
../../../../../../cisco-dpdk-upstream-arm-clang-fixes.git/lib/eal/arm/include/rte_vect.h:80:9: error: argument to '__builtin_neon_vsetq_lane_i32' must be a constant integer
return vsetq_lane_u32(vgetq_lane_u32(b, lane_b), a, lane_a);
^ ~~~~~~
/auto/binos-tools/llvm14/llvm-14.0-p24/lib/clang/14.0.5/include/arm_neon.h:24150:24: note: expanded from macro 'vsetq_lane_u32'
__ret = (uint32x4_t) __builtin_neon_vsetq_lane_i32(__s0, (int32x4_t)__s1, __p2); \
^ ~~~~
2 errors generated.



clang14 does appear to support the vcopyq_laneq_u32() intrinsic, s0 we want to skip the conditional implementation.

Two approaches I have tested to resolve the error are:

1) skip if building with clang:

#if !defined(__clang__) && ((defined(RTE_ARCH_ARM) && defined(RTE_ARCH_32)) || \
72 (defined(RTE_ARCH_ARM64) && RTE_CC_IS_GNU && (GCC_VERSION < 70000)))


2) skip if not building for ARMv7:


#if (defined(RTE_ARCH_ARMv7) && defined(RTE_ARCH_32)) || \
(defined(RTE_ARCH_ARM64) && RTE_CC_IS_GNU && (GCC_VERSION < 70000))


Both address our immediate problem, but may not be a appropriate for all cases.

Can anyone suggest the proper way to address this?  I'll be submitting an patch once I have a solution that is acceptable to the community.
Regards,
Roger











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