[LLVMdev] Fix the aggressive anti-dep breaker's subregister definition handling

[Daniil Troshkov]

Oops! I'm sorry. Misprint:


KillIndices[*SubR] > KillIndices[*AI]

On Sat, Jan 24, 2015 at 8:05 PM, Daniil Troshkov <troshkovdanil at gmail.com>
wrote:

> Hello Hal!
>
> r 202294
> Fix the aggressive anti-dep breaker's subregister definition handling
>
> There is a problem.
>
> For example:
> r0.64 = {r0.32, r1.32}
> r2.64 = {r2.32, r3.32)
>
> def1(r0.32)
> def2(r1.32)
> def3(r0.32)
> use(r0.64)
>
> Try to rename def1(r0.32). According current algo we get smth like:
>
> def1(r2.32)
> def2(r1.32)
> def3(r0.32)
> use(r2.64)
>
> Because r0.64 was still not defined.
>
> Patch to fix it:
>
> Index: lib/CodeGen/AggressiveAntiDepBreaker.cpp
> ===================================================================
> --- lib/CodeGen/AggressiveAntiDepBreaker.cpp (revision 227005)
> +++ lib/CodeGen/AggressiveAntiDepBreaker.cpp (working copy)
> @@ -326,6 +326,7 @@
>  void AggressiveAntiDepBreaker::PrescanInstruction(MachineInstr *MI,
>                                                    unsigned Count,
>                                               std::set<unsigned>&
> PassthruRegs) {
> +  std::vector<unsigned> &KillIndices = State->GetKillIndices();
>    std::vector<unsigned> &DefIndices = State->GetDefIndices();
>    std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
>      RegRefs = State->GetRegRefs();
> @@ -396,7 +397,7 @@
>
>      // Update def for Reg and aliases.
>      for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
> -      // We need to be careful here not to define already-live super
> registers.
> +      // We need to be careful here to define already-live super
> registers.
>        // If the super register is already live, then this definition is
> not
>        // a definition of the whole super register (just a partial
> insertion
>        // into it). Earlier subregister definitions (which we've not yet
> visited
> @@ -403,7 +404,16 @@
>        // because we're iterating bottom-up) need to be linked to the same
> group
>        // as this definition.
>        if (TRI->isSuperRegister(Reg, *AI) && State->IsLive(*AI))
> -        continue;
> +        for (MCSubRegIterator SubR(*AI, TRI, false); SubR.isValid();
> ++SubR)
> +          if (!TRI->isSubRegister(*SubR, Reg) &&
> +              // We get only not defined *SubR.
> +              // If *SubR was defined then *AI is not live but it is.
> +              // So we can use IsLive check for *SubR.
> +              (!State->IsLive(*SubR) ||
> +               KillIndices[*SubR] < KillIndices[*AI])) {
> +            KillIndices[*SubR] = KillIndices[*AI];
> +            DefIndices[*SubR] = DefIndices[*AI];
> +          }
>
>        DefIndices[*AI] = Count;
>      }
>
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