[llvm] DAG: Use phi to create vregs instead of the constant input (PR #129464)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> This commit looks to be the source of a miscompile. [129464-reproducer.zip]

Having not looked at the test at all, does https://github.com/llvm/llvm-project/pull/130776 help?

https://github.com/llvm/llvm-project/pull/129464