29 lines
946 B
Rust
29 lines
946 B
Rust
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// This test case checks that LLVM is aware that computing the size of a slice cannot wrap.
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// The possibility of wrapping results in an additional branch when dropping boxed slices
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// in some situations, see https://github.com/rust-lang/rust/issues/96497#issuecomment-1112865218
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// compile-flags: -O
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#![crate_type="lib"]
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// CHECK-LABEL: @simple_size_of_nowrap
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#[no_mangle]
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pub fn simple_size_of_nowrap(x: &[u32]) -> usize {
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// Make sure the shift used to compute the size has a nowrap flag.
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// CHECK: [[A:%.*]] = shl nsw {{.*}}, 2
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// CHECK-NEXT: ret {{.*}} [[A]]
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core::mem::size_of_val(x)
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}
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// CHECK-LABEL: @drop_write
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#[no_mangle]
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pub fn drop_write(mut x: Box<[u32]>) {
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// Check that this write is optimized out.
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// This depends on the size calculation not wrapping,
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// since otherwise LLVM can't tell that the memory is always deallocated if the slice len > 0.
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// CHECK-NOT: store i32 42
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x[1] = 42;
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}
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