[PATCH] Fix DCE REG_LIBCALL note moving from noop move insns (PR rtl-optimization/33644)
Paolo Bonzini
paolo.bonzini@lu.unisi.ch
Fri Oct 19 17:23:00 GMT 2007
> Adding REG_EQUAL note was all that was needed for CSEing it, but dce.c still
> won't delete it, because it punts on all UNSPECs. The UNSPECs are really
> necessary for the __tls_get_addr call, as the call_insn has mandatory insn
> sequence that needs to be output there (to make TLS transitions possible).
>
> Say speculative moves use UNSPEC_LDS{,A}, but they certainly should be dced.
I would say that all non-trapping UNSPECs (not UNSPEC_VOLATILEs) should
be DCEd. Maxim Kuvyrkov recently added a target hook to mark some
unspecs as non-trapping, and speculative moves are exactly the once he
needed the hook for.
Paolo
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