[llvm-branch-commits] [llvm] backport: [RISCV] Sources of vmerge shouldn't overlap V0 (#170070) (PR #170604)

[Pengcheng Wang via llvm-branch-commits]

wangpc-pp wrote:

> LGTM. FWIW this fixes a miscompile, and the test diffs are largely due to permutations in register allocation if that's of any context. But I'll leave it to @wangpc-pp to comment about the urgency of the backport

Thanks! @lukel97 

@dyung I think this should be included in the 21.x release because this fixes a miscompile (https://github.com/llvm/llvm-project/issues/169905) which existed since LLVM 20.x. If we don't fix it in 21.x, we will have two releases that have this problem. The diffs look large because the candidate registers of `vmerge` instructions have changed, which results in different register allocation results. We have tested llvm-testsuite with this PR and there is no correctness issue.

https://github.com/llvm/llvm-project/pull/170604