Register allocation panic in Wasmtime v0.35.2

[ulan]

After upgrading to version 0.35.2 we are seeing register allocation panics in our integration tests:

thread '<unnamed>' panicked at 'register allocation: Analysis(EntryLiveinValues([v430V]))',
cranelift-codegen-0.82.2/src/machinst/compile.rs:98:10

The panic seems to be fixed on the main branch.

The regression bisects to #3682 and the fix bisects to #3934, which looks related because v430V appears in ucomiss instructions:

  Inst 893:   cmovnzq %v588J, %v429J; cmovpq  %v588J, %v429J
  Inst 894:   xorps   %v585V, %v585V
  Inst 895:   ucomiss %v585V, %v430V
  Inst 896:   setp    %v586Jb

I can share the complete output of VCode_ShowWithRRU if that would help.

I don't have a standalone Wasm file that reproduces this panic, but I can try to extract it from the integration test if that would help.

[ulan]

@abrown @cfallin: Should #3934 be cherry-picked to v0.35?

[cfallin]

@ulan thanks for this report; it certainly looks like the bug that we fixed in #3934. I'm trying to work out now what happened, and it looks like at the time we made the fix, we missed that the original bug was old enough to have gone out in the 0.35 release. I will go ahead with the patch-release process and prepare 0.35.3 with the fix.

[ulan]

Thanks for the fast response and cherry-pick @cfallin!

[cfallin]

@ulan this workflow is running now to publish new crates for 0.35.3; please let us know if there are any other issues! I'll go ahead and close this issue now.