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Auto merge of #101963 - scottmcm:from-ptr-range-optimization, r=Mark-…
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…Simulacrum

Add a codegen test for `slice::from_ptr_range`

I noticed back in #95579 that this didn't optimize as well as it should.

It's better now, after #95837 changed the code in `from_ptr_range` and llvm/llvm-project#54824 was fixed in LLVM 15.

So here's a test to keep it generating the good version.
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bors committed Sep 18, 2022
2 parents 4c2e500 + 3356902 commit a29f341
Showing 1 changed file with 23 additions and 0 deletions.
23 changes: 23 additions & 0 deletions src/test/codegen/slice_as_from_ptr_range.rs
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// compile-flags: -O
// only-64bit (because we're using [ui]size)
// ignore-debug (because the assertions get in the way)
// min-llvm-version: 15.0 (because this is a relatively new instcombine)

#![crate_type = "lib"]
#![feature(slice_from_ptr_range)]

// This is intentionally using a non-power-of-two array length,
// as that's where the optimization differences show up

// CHECK-LABEL: @flatten_via_ptr_range
#[no_mangle]
pub fn flatten_via_ptr_range(slice_of_arrays: &[[i32; 13]]) -> &[i32] {
// CHECK-NOT: lshr
// CHECK-NOT: udiv
// CHECK: mul nuw nsw i64 %{{.+}}, 13
// CHECK-NOT: lshr
// CHECK-NOT: udiv
let r = slice_of_arrays.as_ptr_range();
let r = r.start.cast()..r.end.cast();
unsafe { core::slice::from_ptr_range(r) }
}

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