cmd/internal/obj/ppc64: T/S bit is being flipped when using extended mnemonics in VSX instructions #30112
Description
What version of Go are you using (go version)?
go1.12
Does this issue reproduce with the latest release?
Yes.
What operating system and processor architecture are you using (go env)?
go env Output
linux/ppc64le linux/ppc64
What did you do?
CL160429 uncovered a bug in the assembler, where bit 31 of XX1-form instructions is flipped when using extended mnemonics (FP/VMX registers as arguments, instead of VSX).
What did you expect to see?
F0-F31 must map into VS0-VS13 and V0-V31 must map into VS32-VS63.
What did you see instead?
The problem makes FP register arguments become VMX registers (or, in VSX terms, VS0-VS31 into VS32-VS63). This doesn't cause an illegal instruction, but may cause register clobbering.