[Clang][Driver] Handle LoongArch multiarch tuples

[xen0n]

Summary

This follows v1.00 of the LoongArch Toolchain Conventions.

Only loongarch64 is implemented in Linux::getMultiarchTriple
because support for LA32 and ILP32* ABIs are incomplete right now.

[SixWeining]

clang/lib/Driver/ToolChains/Linux.cpp

41

Missing test. Perhaps add some in clang/test/Driver/linux-ld.c and clang/test/Driver/linux-header-search.cpp? Or postpone this change until loongarch is upstreamed to Debian?

93

Should only check {GNU|GNUF32|GNUF64}?

95

Should only check Triple::Musl?

[MaskRay]

clang/lib/Driver/ToolChains/Linux.cpp

116

return (... + ...).str(); if an operand of + is a Twine

[xen0n]

rebase

[xen0n]

clang/lib/Driver/ToolChains/Linux.cpp

41

Thanks, I'll try adding the tests in the next revision.

But given the recent reversal of upstream dpkg support (apparently due to miscommunication) it may be prudent to wait until a consensus is reached Debian-side.

93

While technically only gnu{,sf,f32,f64} are permitted by the LoongArch Toolchain Conventions (with the bare -gnu being somewhat de-facto standard but not officially so), I believe the user's intent to specify a GNU environment still holds even in cases of "errors" like applying "gnuabi64" or "gnueabi" to LoongArch. Same applies for the musl case.

95

Explained above in the GNU case.

116

Thanks, will change in next revision.

[SixWeining]

clang/lib/Driver/ToolChains/Arch/LoongArch.cpp

66

Better to be f? (Probably most 32-bit hardwares do not support double-float? But I'm not sure about this.)

clang/lib/Driver/ToolChains/Linux.cpp

41

The multiarch tuples have been upstreamed to dpkg. I think we can amend the change and move on now.

[xry111]

clang/lib/Driver/ToolChains/Arch/LoongArch.cpp

66

The ISA manual says 64-bit float support is not limited by 32-bit basic ISA support (except the moving instructions accessing 64-bit GPR).