[NEON] Wrong result of NEON intrinsic vld2q_dup_p16 with the -march=armv7-a flag in CLANG-15.

[yyctw]

According to the ARM documentation https://developer.arm.com/architectures/instruction-sets/intrinsics/vld2q_dup_p16, vld2q_dup_p16 loads a 2-element structure from memory and replicates the structure to all the lanes of the two SIMD&FP registers.
The expected result should be as follows:

poly16_t a[2] = {1, 3};
poly16x8x2_t r = vld2q_dup_p16(a);
// The value of r {1, 1, 1, 1, 1, 1, 1, 1,
//                 3, 3, 3, 3, 3, 3, 3, 3}

However, the result of vld2q_dup_p8 with the flags -march=armv7-a and -mfpu=neon in CLANG-15 is as follows:

poly16_t a[2] = {1, 3};
poly16x8x2_t r = vld2q_dup_p16(a);
// The value of r {3, 3, 3, 3, 1, 1, 1, 1,
//                 0, 0, 0, 0, 3, 3, 3, 3}

This issue also occurs in vld2q_dup_p8.

Reproduce problem: https://godbolt.org/z/6ETT3rjKo
CLANG version:

Debian clang version 15.0.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Thank you for your reading.

[llvmbot]

@llvm/issue-subscribers-backend-arm

Author: Yi-Yen Chung (yyctw)

According to the ARM documentation https://developer.arm.com/architectures/instruction-sets/intrinsics/vld2q_dup_p16, `vld2q_dup_p16` loads a 2-element structure from memory and replicates the structure to all the lanes of the two SIMD&FP registers. The expected result should be as follows: ``` poly16_t a[2] = {1, 3}; poly16x8x2_t r = vld2q_dup_p16(a); // The value of r {1, 1, 1, 1, 1, 1, 1, 1, // 3, 3, 3, 3, 3, 3, 3, 3} ``` However, the result of `vld2q_dup_p8` with the flags `-march=armv7-a` and `-mfpu=neon` in CLANG-15 is as follows: ``` poly16_t a[2] = {1, 3}; poly16x8x2_t r = vld2q_dup_p16(a); // The value of r {3, 3, 3, 3, 1, 1, 1, 1, // 0, 0, 0, 0, 3, 3, 3, 3} ``` This issue also occurs in `vld2q_dup_p8`.

Reproduce problem: https://godbolt.org/z/6ETT3rjKo
CLANG version:

Debian clang version 15.0.7
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

Thank you for your reading.

[EugeneZelenko]

@yyctw: Please always try to test latest release (only supported) and main.

[yyctw]

@yyctw: Please always try to test latest release (only supported) and main.

Thank you for the reminder. This is the result after the change: https://godbolt.org/z/bP4d18YMh

[davemgreen]

I think this is an example of it going wrong: https://godbolt.org/z/hevqGKfqj

The VLD2DUPq16EvenPseudo/VLD2DUPq16OddPseudo pseudos don't look well defined, there is no register dependency between them.

[AlfieRichardsArm]

Fix proposed: #79287

[AlfieRichardsArm]

@yyctw This should now be fixed in llvm main, and should be included in the next release. Thank you for the bug report.