[CIR] Use cir.get_vptr to initialize vptr members #1784
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andykaylor
requested review from
xlauko,
bcardosolopes,
mmha,
erichkeane and
lanza
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@tommymcm As previously discussed |
andykaylor
commented
Aug 8, 2025
| // CIR: %{{[0-9]+}} = cir.load align(8) %{{[0-9]+}} : !cir.ptr<!cir.ptr<!void>>, !cir.ptr<!void> | ||
| // CIR: %{{[0-9]+}} = cir.cast(bitcast, %{{[0-9]+}} : !cir.ptr<!rec_B>), !cir.ptr<!cir.ptr<!void>> | ||
| // CIR: cir.store{{.*}} %{{[0-9]+}}, %{{[0-9]+}} : !cir.ptr<!void>, !cir.ptr<!cir.ptr<!void>> | ||
| // CIR: %{{[0-9]+}} = cir.cast(bitcast, %{{[0-9]+}} : !cir.ptr<!cir.ptr<!void>>), !cir.ptr<!cir.vptr> |
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Ideally, cir.vtt.address_point would return !cir.ptr<!cir.vptr> but that introduces a problem with creating the argument list for constructors that require a VTT parameter. We're using QualType extensively in the argument list handling, and there is no QualType that corresponds to !cir.vptr. We use 'pointer-to-pointer-to-void', which is a close equivalent.
I think I can update cir.vtt.address_point and just insert bitcasts when it's used as an argument, but until then, it's 'pointer-to-pointer-to-void'.
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Sorry for the rebase churn, this PR needs updating! |
Previously, following classic codegen, we were using a bitcast to get the address of the vptr member when initializing the vptr in a constructor. This change updates the handling to use cir.get_vptr instead. This is functionally equivalent because the vptr is always at offset zero for the CXXABIs we currently support, but using cir.get_vptr makes what we are doing more explicit.
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Previously, following classic codegen, we were using a bitcast to get the address of the vptr member when initializing the vptr in a constructor. This change updates the handling to use cir.get_vptr instead.
This is functionally equivalent because the vptr is always at offset zero for the CXXABIs we currently support, but using cir.get_vptr makes what we are doing more explicit.