[llvm] [AMDGPU] Skip terminators when forcing emit zero flag (PR #112116)

[Shilei Tian via llvm-commits]

shiltian wrote:

> Why do you say "non-first terminators" in the description?

Updated the description. The first version indeed only considered non-first terminators.

> In the test case, why does SIInsertWaitcnts want to put a wait between the two branch instructions?

Because we force emit zero via `amdgpu-waitcnt-forcezero`. That is a debug switch, but didn't work properly in some cases.

https://github.com/llvm/llvm-project/pull/112116