[flang][hlfir] Lower Cray pointee references. #65563
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A Cray pointee reference must be done using the characteristics (bounds, type params) of the original pointee declaration, but using the actual address value of the associated Cray pointer. There might be multiple Cray pointees associated with the same Cray pointer. The proposed solution is to lower each Cray pointee into a POINTER variable with a descriptor. The descriptor is initialized at the point of declaration of the pointee, though its base_addr is set to null. Before each reference of the Cray pointee its descriptor's base_addr is updated to the current value of the Cray pointer. The update of the base_addr is done using PointerAssociateScalar runtime call, which just updates the base_addr of the descriptor. This is a temporary solution just to make Cray pointers work to the same extent they work with FIR lowering.
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| mlir::Value boxAlloc = | ||
| fir::factory::genNullBoxStorage(builder, loc, ptrBoxType); |
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This code allocates and initialize the pointer storage, I think the initialization is not needed/confusing in the generated IR given it is done again with the actual shape info below.
Maybe you can just use builder.createTemporary(loc, ptrBoxType) to get the temp and move the initialization code you have below before the hlfir.declare. That way, at the point of the hlfir.declare, the pointer contains the right shape/length info.
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Yes, createTemporary should be cleaner, and I will fix it. Thank you!
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I am not sure if moving the initialization code before hlfir.declare is necessary. Do you have an example when this may matter?
Right now the IR looks like we have a regular local pointer with the missing initialization of the pointer into an unassociated status. Since the following initialization happens before any possible use, I would say it does not matter whether it happens before or after hlfir.declare, but I may be missing something.
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It is not necessary, this was a (very minor) personal opinion regarding the readability of the generated IR. I am also fine with the way it is.
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Oh, okay. Thank you for the clarification!
| ! CHECK: %[[VAL_25:.*]] = fir.zero_bits !fir.ptr<!fir.array<?x!fir.char<1,11>>> | ||
| ! CHECK: %[[VAL_26:.*]] = arith.constant 0 : index | ||
| ! CHECK: %[[VAL_27:.*]] = fir.shape %[[VAL_26]] : (index) -> !fir.shape<1> | ||
| ! CHECK: %[[VAL_28:.*]] = fir.embox %[[VAL_25]](%[[VAL_27]]) : (!fir.ptr<!fir.array<?x!fir.char<1,11>>>, !fir.shape<1>) -> !fir.box<!fir.ptr<!fir.array<?x!fir.char<1,11>>>> | ||
| ! CHECK: fir.store %[[VAL_28]] to %[[VAL_2]] : !fir.ref<!fir.box<!fir.ptr<!fir.array<?x!fir.char<1,11>>>>> |
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This is the part that I find confusing given it is set again after the hlfir.declare with the "correct" information,
A Cray pointee reference must be done using the characteristics
(bounds, type params) of the original pointee declaration, but
using the actual address value of the associated Cray pointer.
There might be multiple Cray pointees associated with the same
Cray pointer.
The proposed solution is to lower each Cray pointee into a POINTER
variable with a descriptor. The descriptor is initialized at the point
of declaration of the pointee, though its base_addr is set to null.
Before each reference of the Cray pointee its descriptor's base_addr
is updated to the current value of the Cray pointer.
The update of the base_addr is done using PointerAssociateScalar
runtime call, which just updates the base_addr of the descriptor.
This is a temporary solution just to make Cray pointers work
to the same extent they work with FIR lowering.