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[flang][cuda] Update condition in descriptor data transfer #148306

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Jul 11, 2025
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[flang][cuda] Update condition in descriptor data transfer #148306

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6 changes: 2 additions & 4 deletions flang-rt/lib/cuda/memory.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -110,14 +110,12 @@ void RTDECL(CUFDataTransferDescDesc)(Descriptor *dstDesc, Descriptor *srcDesc,
dstDesc->ApplyMold(*srcDesc, dstDesc->rank());
dstDesc->Allocate(/*asyncObject=*/nullptr);
}
if ((srcDesc->rank() > 0) && (dstDesc->Elements() < srcDesc->Elements())) {
if ((srcDesc->rank() > 0) && (dstDesc->Elements() <= srcDesc->Elements()) &&
srcDesc->IsContiguous() && dstDesc->IsContiguous()) {
// Special case when rhs is bigger than lhs and both are contiguous arrays.
// In this case we do a simple ptr to ptr transfer with the size of lhs.
// This is be allowed in the reference compiler and it avoids error
// triggered in the Assign runtime function used for the main case below.
if (!srcDesc->IsContiguous() || !dstDesc->IsContiguous())
terminator.Crash("Unsupported data transfer: mismatching element counts "
"with non-contiguous arrays");
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Is my understanding correct that both new and old version achieve the same goal of only allowing contiguous arrays for the data transfer, but the old version gives an error message about unsupported data transfer?

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Ah! I see there is a difference between <= and <. Didn't notice it.

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Yeah and the new version fall back on the runtime assign function instead of giving an error.

RTNAME(CUFDataTransferPtrPtr)(dstDesc->raw().base_addr,
srcDesc->raw().base_addr, dstDesc->Elements() * dstDesc->ElementBytes(),
mode, sourceFile, sourceLine);
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