rustc_codegen_ssa: use bitcasts instead of type punning for scalar transmutes. #79801
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Dec 9, 2020
| #[no_mangle] | ||
| pub unsafe fn byte_to_bool(byte: u8) -> bool { | ||
| std::mem::transmute(byte) | ||
| } |
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Can you add special test around the pointer special case? (ptr->ptr, ptr->int, ...) I don't anticipate this PR breaking it, but it would be good to have it to be sure.
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Good point, added ptr->ptr, ptr->int, int->ptr, and included comments with what they might become in the future.
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@bors r=nagisa |
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📌 Commit 5c1d2ce has been approved by |
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⌛ Testing commit 5c1d2ce with merge ed6739a8568aa29b8a1aa17d7af76b8e1859cc47... |
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💔 Test failed - checks-actions |
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Oops, guess the tests needs @bors r=nagisa |
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📌 Commit 718fba9 has been approved by |
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☀️ Test successful - checks-actions |
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This specifically helps with
f32<->u32(from_bits,to_bits) in Rust-GPU (rustc_codegen_spirv), where (AFAIK) we don't yet have enough infrastructure to turn type punning memory accesses into SSA bitcasts.(There may be more instances, but the one I've seen myself is
f32::signumfromnum-traitsinspecting e.g. the sign bit)Sadly I've had to make an exception for
transmutes between pointers and non-pointers, as LLVM disallows usingbitcastfor them.r? @nagisa cc @khyperia