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Add codegen test for removing trailing zeroes from NonZero #145393

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Add codegen test for removing trailing zeroes from NonZero #145393

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17 changes: 17 additions & 0 deletions tests/codegen-llvm/issues/issue-138497-nonzero-remove-trailing-zeroes.rs
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Original file line number Diff line number Diff line change
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//! This test checks that removing trailing zeroes from a `NonZero`,
//! then creating a new `NonZero` from the result does not panic.

//@ min-llvm-version: 21
//@ compile-flags: -O -Zmerge-functions=disabled
#![crate_type = "lib"]

use std::num::NonZero;

// CHECK-LABEL: @remove_trailing_zeros
#[no_mangle]
pub fn remove_trailing_zeros(x: NonZero<u8>) -> NonZero<u8> {
// CHECK-NOT: unwrap_failed
// CHECK-NOT: br
// CHECK ret i8
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Maybe check the exact instruction sequence?

  %0 = tail call range(i8 0, 9) i8 @llvm.cttz.i8(i8 %x, i1 true)
  %n = lshr exact i8 %x, %0
  ret i8 %n

It seems unlikely to change from cttz + lshr + ret, and that seems less brittle than checking for absence of particular words (br/unwrap).

NonZero::new(x.get() >> x.trailing_zeros()).unwrap()
}
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