Rework profiled to nop guard upgrades in VP - #6752
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October 5, 2022 15:40
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This change looks good to me. |
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Jenkins build all |
For all profiled guards (VFT test or method test), when the guard is not folded, replace it with a noppable guard if possible. Replacing a VFT test with a noppable guard is possible when there is a type bound C for the receiver, and C is the type expected by the VFT test, and C has not been extended. It's as though C is final (which would allow folding via a fixed-type constraint), but only until further notice. Replacing a method test with a noppable guard is possible when there is a type bound C for the receiver, and C has the expected method, and the expected method is not overridden. It's as though the expected method is final (which would allow folding), but only until further notice. By default such upgrades are performed only outside of the VM startup phase, since during startup the VM is still loading classes pretty frequently, so the non-extended or nonoverridden state is not as significant. To enable the transformation during startup, set the environment variable TR_upgradeToNopGuardDuringStartup. A new query VMEnv::isVMInStartupPhase(TR::Compilation*) is defined to detect this startup phase. It is intended for downstream projects to override. The default implementation arbitrarily returns false. There was pre-existing code that attempted to change profiled guards into nop guards, but it worked only for VFT tests, and only when the cold call was a virtual call (although part of the code appeared to be trying to handle interface calls). The new implementation also works for method tests and for interface calls, and in the case of method test, the logic that triggers the transformation is largely shared with other recent improvements to the handling of method test. As such, this commit deletes the prior implementation of this concept.
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Build break @jdmpapin |
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Updated to remove a J9-ism |
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Jenkins build all |
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I know @jdmpapin is doing some more personal testing, and so I will await what he gets from that before I merge this. |
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My testing has passed - this is good to go |
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For all profiled guards (VFT test or method test), when the guard is not folded, replace it with a noppable guard if possible.
Replacing a VFT test with a noppable guard is possible when there is a type bound C for the receiver, and C is the type expected by the VFT test, and C has not been extended. It's as though C is final (which would allow folding via a fixed-type constraint), but only until further notice.
Replacing a method test with a noppable guard is possible when there is a type bound C for the receiver, and C has the expected method, and the expected method is not overridden. It's as though the expected method is final (which would allow folding), but only until further notice.
By default such upgrades are performed only outside of the VM startup phase, since during startup the VM is still loading classes pretty frequently, so the non-extended or nonoverridden state is not as significant. To enable the transformation during startup, set the environment variable
TR_upgradeToNopGuardDuringStartup.A new query
VMEnv::isVMInStartupPhase(TR::Compilation*)is defined to detect this startup phase. It is intended for downstream projects to override. The default implementation arbitrarily returns false.There was pre-existing code that attempted to change profiled guards into nop guards, but it worked only for VFT tests, and only when the cold call was a virtual call (although part of the code appeared to be trying to handle interface calls). The new implementation also works for method tests and for interface calls, and in the case of method test, the logic that triggers the transformation is largely shared with other recent improvements to the handling of method test. As such, this commit deletes the prior implementation of this concept.