Block SIMD in transmute_immediate; delete OperandValueKind
#143410
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r? @SparrowLii rustbot has assigned @SparrowLii. Use |
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Some changes occurred in compiler/rustc_codegen_ssa |
scottmcm
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Jul 4, 2025
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| let in_a_ibty = bx.scalar_pair_element_backend_type(operand.layout, 0, false); | ||
| let in_b_ibty = bx.scalar_pair_element_backend_type(operand.layout, 1, false); | ||
| let out_a_ibty = bx.scalar_pair_element_backend_type(cast, 0, false); | ||
| let out_b_ibty = bx.scalar_pair_element_backend_type(cast, 1, false); |
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These just disappear entirely because transmute_immediate no longer needs them as arguments 🎉
RalfJung
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Jul 4, 2025
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At this point I am happy with the codegen changes, but I have a hard time interpreting the test changes. Wouldn't mind someone else to take a look at those :) |
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Vectors have been causing me problems for years in this code, for example #110021 (comment) and #143194
See conversation in https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Is.20transmuting.20a.20.60T.60.20to.20.60Tx1.60.20.28one-element.20SIMD.20vector.29.20UB.3F/near/526262799.
By blocking SIMD in
transmute_immediateit can be simplified to just take theScalars involved -- the backend types can be gotten from thoseScalars, rather than needing to be passed. And there's an assert added to ICE it if it does get hit.Accordingly, this changes
rvalue_creates_operandto not send SIMD transmutes through the operand path, but to always go through memory instead, like they did back before #108442.And thanks to those changes, I could also remove the
OperandValueKindtype that I added back then which @RalfJung rightly considers pretty sketchy.cc @folkertdev @workingjubilee from the zulip conversation too