[llvm-dev] isHardwareLoopProfitable() called with empty assumption cache in hwloops pass

[Janek Van Oirschot via llvm-dev]

Hey all,

It seems that when HardwareLoops calls the isHardwareLoopProfitable TTI hook, it never has a populated AssumptionCache. Some debugging revealed that HardwareLoops runs during the PreISel phase for ARM and PPC. However, the CodeGenPrepare pass runs before PreISel and removes all assumes meaning that the AssumptionCache in HardwareLoops will end up empty.

From what I gather (and let me know if I'm wrong), only PPC uses the AssumptionCache in isHardwareLoopProfitable but only to aid in some cost analysis. I was wondering whether it's intended behaviour to have an empty AssumptionCache during HardwareLoops? I ask because I was looking into using assumes to persuade HardwareLoops into emitting hardware intrinsics for our (downstream) target.

Kind regards,
Janek van Oirschot

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