tree cc5c0683ff3a6b569e6d4d2ce5115062641bb8dd
parent c75b449af658351186d2832909a8a28800600312
author Alex Bradbury <asb@lowrisc.org> 1537354462 +0000
committer Alex Bradbury <asb@lowrisc.org> 1537354462 +0000

[RISCV] Codegen for i8, i16, and i32 atomicrmw with RV32A

Introduce a new RISCVExpandPseudoInsts pass to expand atomic 
pseudo-instructions after register allocation. This is necessary in order to 
ensure that register spills aren't introduced between LL and SC, thus breaking 
the forward progress guarantee for the operation. AArch64 does something 
similar for CmpXchg (though only at O0), and Mips is moving towards this 
approach (see D31287). See also [this mailing list 
post](http://lists.llvm.org/pipermail/llvm-dev/2016-May/099490.html) from 
James Knight, which summarises the issues with lowering to ll/sc in IR or 
pre-RA.

See the [accompanying RFC 
thread](http://lists.llvm.org/pipermail/llvm-dev/2018-June/123993.html) for an 
overview of the lowering strategy.

Differential Revision: https://reviews.llvm.org/D47882


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342534 91177308-0d34-0410-b5e6-96231b3b80d8