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4e886d6876
Avoid using the `copy_nonoverlapping` wrapper through `mem::replace`. This is a much simpler way to achieve the pre-#86003 behavior of `mem::replace` not needing dynamically-sized `memcpy`s (at least before inlining), than re-doing #81238 (which needs #86699 or something similar). I didn't notice it until recently, but `ptr::write` already explicitly avoided using the wrapper, while `ptr::read` just called the wrapper (and was the reason for us observing any behavior change from #86003 in Rust-GPU). <hr/> The codegen test I've added fails without the change to `core::ptr::read` like this (ignore the `v0` mangling, I was using a worktree with it turned on by default, for this): ```llvm 13: ; core::intrinsics::copy_nonoverlapping::<u8> 14: ; Function Attrs: inlinehint nonlazybind uwtable 15: define internal void `@_RINvNtCscK5tvALCJol_4core10intrinsics19copy_nonoverlappinghECsaS4X3EinRE8_25mem_replace_direct_memcpy(i8*` %src, i8* %dst, i64 %count) unnamed_addr #0 { 16: start: 17: %0 = mul i64 %count, 1 18: call void `@llvm.memcpy.p0i8.p0i8.i64(i8*` align 1 %dst, i8* align 1 %src, i64 %0, i1 false) not:17 !~~~~~~~~~~~~~~~~~~~~~ error: no match expected 19: ret void 20: } ``` With the `core::ptr::read` change, `core::intrinsics::copy_nonoverlapping` doesn't get instantiated and the test passes. <hr/> r? `@m-ou-se` cc `@nagisa` (codegen test) `@oli-obk` / `@RalfJung` (miri diagnostic changes) |
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