[llvm] [VPlan] Fix header phi VPInstruction verification. NFC (PR #151472)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Maybe just do a prefix-matching?

I wish I could, but doesn't look like there's a GTEST macro for prefixes unfortunately. I've just copied what the other tests have done and pushed a fix in 3e579d93ab50952628a51bda05f3a39f6a5a631c



https://github.com/llvm/llvm-project/pull/151472