testing: within a B.Loop loop, assigning function result to _ allows body to be optimized away (1.26 regression) [1.26 backport]

[gopherbot]

@cherrymui requested issue #77654 to be considered for backport to the next 1.26 minor release.

@gopherbot please backport this to Go 1.26. This is a regression from 1.25. Thanks

[cagedmantis]

Approved. This is a regression.

[dmitshur]

@JunyangShao This backport issue is approved, and it needs a backport CL to be created as the next step here. Since you authored the original CL, mind doing that? Note that there is a merge conflict that needs resolution. Thanks.

[prattmic]

It looks like the conflicts are due to https://go.dev/cl/728961 refactoring a bunch of this package, but that mostly just deduplicates code, so I think it should be possible to do the backport manually without also backporting https://go.dev/cl/728961.

[gopherbot]

Change https://go.dev/cl/772122 mentions this issue: [release-branch.go1.26] cmd/compile: keep blank nodes alive in b.loop

[gopherbot]

Closed by merging CL 772122 (commit 722b68c) to release-branch.go1.26.