MIR: hide .rodata constants vs by-ref ABI clash in trans. #45996
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kennytm
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LGTM, I'll let @arielb1 have a look first though |
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r? @arielb1 |
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@bors r+ |
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kennytm
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@bors r=arielb1 |
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☔ The latest upstream changes (presumably #45825) made this pull request unmergeable. Please resolve the merge conflicts. |
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@bors r=arielb1 |
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MIR: hide .rodata constants vs by-ref ABI clash in trans. Back in #45380, constants were copied into locals during MIR creation to ensure that arguments ' memory can be used by the callee, if the constant is placed in `.rodata` and the ABI passes it by-ref. However, there are several drawbacks (see #45380 (comment)), most importantly the complication of constant propagation (UB if a constant ends up in `Call` arguments) and inconveniencing analyses. Instead, I've modified the `rustc_trans` implementation of calls to copy an `Operand::Constant` argument locally if it's not immediate, and added a test that segfaults without the copy. cc @dotdash @arielb1
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Back in #45380, constants were copied into locals during MIR creation to ensure that arguments ' memory can be used by the callee, if the constant is placed in
.rodataand the ABI passes it by-ref.However, there are several drawbacks (see #45380 (comment)), most importantly the complication of constant propagation (UB if a constant ends up in
Callarguments) and inconveniencing analyses.Instead, I've modified the
rustc_transimplementation of calls to copy anOperand::Constantargument locally if it's not immediate, and added a test that segfaults without the copy.cc @dotdash @arielb1