RISCV backport request for 10.0.1

[asb]

Bugzilla Link	46378
Resolution	FIXED
Resolved on	Jun 25, 2020 23:33
Version	10.0
OS	Linux
Blocks	#44654
CC	@tstellar
Fixed by commit(s)	616289e

Extended Description

I'd like to please request the following fixes be applied to 10.0.1. I've cherry-picked them locally on a 10.x branch, built, and tested it:

1. 616289e Correctly sign-extend comparison for ATOMIC_CMP_XCHG
2. 7ee479a Fix passing two floating-point values in complex separately by two GPRs on RV64
3. e31ccee Provide muldi3 builtin assembly implementation
4. 64f4172 Fix incorrect FP base CFI offset for variable argument functions
5. 91f7f0d Fix sysroot tests without GCC on RISC-V hosts with GCC (this was necessary to fix clang/test/Driver/riscv{32,64}-toolchain-extra.c failures for me)

1. and 2) in the above are highest priority from my perspective, though I think there's value in picking all of these.

[asb]

In addition, I'd like to request (if possible):
6. 7622ea5: [RISCV64] Emit correct lib call for fp(float/double) to ui/si

This is a useful non-invasive bugfix.

[tstellar]

Can you push that branch somewhere public? That will save me some time.

[asb]

Of course - see https://github.com/asb/llvm-project/tree/riscv-10.0.1

Alternatively, the following works with no intervention needed on the current release/10.x branch:

git cherry-pick -x 91f7f0d
git cherry-pick -x 616289e
git cherry-pick -x 7ee479a
git cherry-pick -x 7622ea5
git cherry-pick -x e31ccee
git cherry-pick -x 64f4172

[asb]

Apologies for missing that one of the patches changes (the ATOMIC_CMP_XCHG fix) modified the libLLVM.so ABI. I've pushed a version of the patch in tstellar#194 that fixes the codegen bug without adding the hook.

[tstellar]

I've merged these.