Avoid a bitcast FFI call in transmuting #142768
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For things that only change the valid ranges, we can just skip the `LLVMBuildBitCast` call. I tried to tweak this a bit more and broke stuff, so I also added some extra tests for that as we apparently didn't have coverage.
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rustbot has assigned @WaffleLapkin. Use |
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@bors r+ rollup |
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did not mean to clone PR... |
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…=WaffleLapkin Avoid a bitcast FFI call in transmuting For things that only change the valid ranges, we can just return the input, rather than making the `LLVMBuildBitCast` call and having *it* then do nothing. I tried to tweak this a bit more and broke stuff, so I also added some extra tests for that as we apparently didn't have coverage.
This was referenced Jun 25, 2025
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Rollup of 15 pull requests Successful merges: - #135731 (Implement parsing of pinned borrows) - #138780 (Add `#[loop_match]` for improved DFA codegen) - #142453 (Windows: make `read_dir` stop iterating after the first error is encountered) - #142633 (Error on invalid signatures for interrupt ABIs) - #142768 (Avoid a bitcast FFI call in transmuting) - #142825 (Port `#[track_caller]` to the new attribute system) - #142844 (Enable short-ice for Windows) - #142934 (Tweak `-Zmacro-stats` measurement.) - #142955 (Couple of test suite fixes for cg_clif) - #142977 (rustdoc: Don't mark `#[target_feature]` functions as ⚠) - #142980 (Reduce mismatched-lifetime-syntaxes suggestions to MaybeIncorrect) - #142982 (Corrected spelling mistake in c_str.rs) - #142983 (Taint body on invalid call ABI) - #142988 (Update wasm-component-ld to 0.5.14) - #142993 (Update cargo) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of #142768 - scottmcm:avoid-unneeded-bitcast, r=WaffleLapkin Avoid a bitcast FFI call in transmuting For things that only change the valid ranges, we can just return the input, rather than making the `LLVMBuildBitCast` call and having *it* then do nothing. I tried to tweak this a bit more and broke stuff, so I also added some extra tests for that as we apparently didn't have coverage.
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Huh, I wasn't expecting anything material from this, but something in #142997 was, so out of curiosity |
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Finished benchmarking commit (4e95f4a): comparison URL. Overall result: ✅ improvements - no action neededBenchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf. @bors rollup=never Instruction countOur most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.
Max RSS (memory usage)Results (primary -1.3%, secondary -1.2%)A less reliable metric. May be of interest, but not used to determine the overall result above.
CyclesResults (secondary -5.0%)A less reliable metric. May be of interest, but not used to determine the overall result above.
Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 689.044s -> 689.011s (-0.00%) |
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Rollup of 15 pull requests Successful merges: - rust-lang/rust#135731 (Implement parsing of pinned borrows) - rust-lang/rust#138780 (Add `#[loop_match]` for improved DFA codegen) - rust-lang/rust#142453 (Windows: make `read_dir` stop iterating after the first error is encountered) - rust-lang/rust#142633 (Error on invalid signatures for interrupt ABIs) - rust-lang/rust#142768 (Avoid a bitcast FFI call in transmuting) - rust-lang/rust#142825 (Port `#[track_caller]` to the new attribute system) - rust-lang/rust#142844 (Enable short-ice for Windows) - rust-lang/rust#142934 (Tweak `-Zmacro-stats` measurement.) - rust-lang/rust#142955 (Couple of test suite fixes for cg_clif) - rust-lang/rust#142977 (rustdoc: Don't mark `#[target_feature]` functions as ⚠) - rust-lang/rust#142980 (Reduce mismatched-lifetime-syntaxes suggestions to MaybeIncorrect) - rust-lang/rust#142982 (Corrected spelling mistake in c_str.rs) - rust-lang/rust#142983 (Taint body on invalid call ABI) - rust-lang/rust#142988 (Update wasm-component-ld to 0.5.14) - rust-lang/rust#142993 (Update cargo) r? `@ghost` `@rustbot` modify labels: rollup
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Idk how, but this is creating miscompilations when casting from Which brings up the question, are these transmutes even valid? Because they are used quite a bit in stdarch (mainly in ARM, which has 1-element SIMD types) |
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For things that only change the valid ranges, we can just return the input, rather than making the
LLVMBuildBitCastcall and having it then do nothing.I tried to tweak this a bit more and broke stuff, so I also added some extra tests for that as we apparently didn't have coverage.