038706986f
Don't re-`assume` in `transmute`s that don't change niches I noticed in nightly 2025-02-21 that `transmute` is emitting way more `assume`s than necessary for newtypes. For example, the three transmutes in <https://rust.godbolt.org/z/fW1KaTc4o> emits ```rust define noundef range(i32 1, 0) i32 `@repeatedly_transparent_transmute(i32` noundef range(i32 1, 0) %_1) unnamed_addr { start: %0 = sub i32 %_1, 1 %1 = icmp ule i32 %0, -2 call void `@llvm.assume(i1` %1) %2 = sub i32 %_1, 1 %3 = icmp ule i32 %2, -2 call void `@llvm.assume(i1` %3) %4 = sub i32 %_1, 1 %5 = icmp ule i32 %4, -2 call void `@llvm.assume(i1` %5) %6 = sub i32 %_1, 1 %7 = icmp ule i32 %6, -2 call void `@llvm.assume(i1` %7) %8 = sub i32 %_1, 1 %9 = icmp ule i32 %8, -2 call void `@llvm.assume(i1` %9) %10 = sub i32 %_1, 1 %11 = icmp ule i32 %10, -2 call void `@llvm.assume(i1` %11) ret i32 %_1 } ``` But those are all just newtypes that don't change size or niches, so none of it's needed. After this PR it's down to just ```rust define noundef range(i32 1, 0) i32 `@repeatedly_transparent_transmute(i32` noundef range(i32 1, 0) %_1) unnamed_addr { start: ret i32 %_1 } ``` because none of those `assume`s in the original actually did anything. (Transmuting to something with a difference niche, though, still has the assumes -- the other tests continue to pass checking that.)
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