Raising: fold null-guarded pointer selects - #2992
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Staging helpers (mfem's Read/Write) return null for empty buffers, so a captured device pointer reaches the kernel as select(size > 0, ptr, null) and the raising fails on the select. When the pointer's value is only ever consumed as the address of a memory access, the null arm can only fault, so the select collapses to the real pointer. Pointers whose value is observed directly (compared, cast to int, stored as data, passed to a call) are left alone. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016zErYp7upmqr4NHfhod9UD
This was referenced Aug 27, 2026
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mfem's staging helpers (
Read()/Write()in device.hpp) return null for empty buffers, so a captured device pointer reaches the kernel asselect(size > 0, ptr, null), and raising fails on the select (hit byEABilinearFormExtension::GetElementMatricesand other assembly paths in the MFEM CUDA campaign, #2968).When the pointer's value is only ever consumed as the address of a memory access (through geps, casts, further selects, or
pointer2memrefviews feeding loads/stores/atomics), the null arm can only fault, so the select collapses to the real pointer. Pointers whose value is observed directly — compared, cast to int, stored as data, passed to a call — are left alone.Includes a lit test where the folded kernel then raises end-to-end.
🤖 Generated with Claude Code
https://claude.ai/code/session_016zErYp7upmqr4NHfhod9UD