[llvm-dev] Lowering Select to Two Predicated Movs
Friedman, Eli via llvm-dev
llvm-dev at lists.llvm.org
Fri Jul 7 14:32:12 PDT 2017
On 7/7/2017 1:34 PM, Dilan Manatunga wrote:
> Ohh, that makes sense. And is the reason the first instruction doesn't
> get deleted because the ExpandPseudoInstructions pass occurs after
> Register Allocation and machine dead code elimination?
That's how it works right now, yes, but it's a bug, not the intended
design. (Post-RA scheduling runs after ExpandPseudoInstructions, so we
need accurate dependencies; I'm surprised we haven't seen any miscompiles.)
The correct way to represent the dependency is with an implicit use.
See UpdatePredRedefs in IfConversion.cpp for an example.
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