Second argument to signed Neon vtbl functions should be unsigned

[llvmbot]

Bugzilla Link	23324
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DavidSpickett

Extended Description

The ARM C Language Extensions document (ACLE) specifies that the second (index) parameter to the vtbl and vtbx family of functions should be unsigned, even when the other parameters are signed:

Aarch32: T vtblN_ST(TxN a, UT b); T vtbxN_ST(T a, TxN b, UT c);

Aarch64: T vqtblNQ_ST (T2xN t, UT idx); T vqtbxNQ_ST (T a, T2xN t, UT idx);

E.g., int8x8_t vqtbl1_s8 (int8x16_t a, uint8x8_t b)

Clang declares them to be signed, instead.

GCC has had these correct for Aarch64 since GCC 4.9, though for ARM (Aarch32) it still has the second value signed.

[DavidSpickett]

This has been fixed, though by what I couldn't find.

The attached test.cpp file using function pointers with types the ACLE expects compiles without error with trunk clang.

(types from here) https://developer.arm.com/architectures/instruction-sets/simd-isas/neon/intrinsics?search=vcls

$ ./clang -target aarch64-arm-none-eabi -march=armv8-a+simd -c -o /dev/null /tmp/test.cpp

[DavidSpickett]

test file