79 lines
2.8 KiB
Rust
79 lines
2.8 KiB
Rust
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// compile-flags: -O
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// min-llvm-version: 15.0 (because we're using opaque pointers)
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// ignore-debug (debug assertions in `slice::from_raw_parts` block optimizations)
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#![crate_type = "lib"]
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// CHECK-LABEL: @align8
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#[no_mangle]
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pub fn align8(p: *const u8) -> bool {
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// CHECK: ret i1 true
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p.align_offset(8) < 8
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}
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#[repr(align(4))]
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pub struct Align4([u8; 4]);
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// CHECK-LABEL: @align_to4
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#[no_mangle]
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pub fn align_to4(x: &[u8]) -> bool {
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// CHECK: ret i1 true
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let (prefix, _middle, suffix) = unsafe { x.align_to::<Align4>() };
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prefix.len() < 4 && suffix.len() < 4
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}
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// CHECK-LABEL: @align_offset_byte_ptr(ptr{{.+}}%ptr)
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#[no_mangle]
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pub fn align_offset_byte_ptr(ptr: *const u8) -> usize {
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// CHECK: %[[ADDR:.+]] = ptrtoint ptr %ptr to [[USIZE:i[0-9]+]]
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// CHECK: %[[UP:.+]] = add [[USIZE]] %[[ADDR]], 31
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// CHECK: %[[ALIGNED:.+]] = and [[USIZE]] %[[UP]], -32
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// CHECK: %[[OFFSET:.+]] = sub [[USIZE]] %[[ALIGNED]], %[[ADDR]]
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// Since we're offsetting a byte pointer, there's no further fixups
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// CHECK-NOT: shr
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// CHECK-NOT: div
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// CHECK-NOT: select
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// CHECK: ret [[USIZE]] %[[OFFSET]]
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ptr.align_offset(32)
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}
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// CHECK-LABEL: @align_offset_word_slice(ptr{{.+}}align 4{{.+}}%slice.0
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#[no_mangle]
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pub fn align_offset_word_slice(slice: &[Align4]) -> usize {
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// CHECK: %[[ADDR:.+]] = ptrtoint ptr %slice.0 to [[USIZE]]
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// CHECK: %[[UP:.+]] = add [[USIZE]] %[[ADDR]], 31
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// CHECK: %[[ALIGNED:.+]] = and [[USIZE]] %[[UP]], -32
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// CHECK: %[[BOFFSET:.+]] = sub [[USIZE]] %[[ALIGNED]], %[[ADDR]]
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// CHECK: %[[OFFSET:.+]] = lshr exact [[USIZE]] %[[BOFFSET]], 2
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// Slices are known to be aligned, so we don't need the "maybe -1" path
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// CHECK-NOT: select
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// CHECK: ret [[USIZE]] %[[OFFSET]]
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slice.as_ptr().align_offset(32)
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}
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// CHECK-LABEL: @align_offset_word_ptr(ptr{{.+}}%ptr
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#[no_mangle]
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pub fn align_offset_word_ptr(ptr: *const Align4) -> usize {
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// CHECK: %[[ADDR:.+]] = ptrtoint ptr %ptr to [[USIZE]]
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// CHECK: %[[UP:.+]] = add [[USIZE]] %[[ADDR]], 31
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// CHECK: %[[ALIGNED:.+]] = and [[USIZE]] %[[UP]], -32
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// CHECK: %[[BOFFSET:.+]] = sub [[USIZE]] %[[ALIGNED]], %[[ADDR]]
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// While we can always get a *byte* offset that will work, if the original
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// pointer is unaligned it might be impossible to return an *element* offset
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// that will make it aligned. We want it to be a `select`, not a `br`, so
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// that the assembly will be branchless.
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// CHECK: %[[LOW:.+]] = and [[USIZE]] %[[ADDR]], 3
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// CHECK: %[[ORIGINAL_ALIGNED:.+]] = icmp eq [[USIZE]] %[[LOW]], 0
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// CHECK: %[[OFFSET:.+]] = lshr exact [[USIZE]] %[[BOFFSET]], 2
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// CHECK: %[[R:.+]] = select i1 %[[ORIGINAL_ALIGNED]], [[USIZE]] %[[OFFSET]], [[USIZE]] -1
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// CHECK: ret [[USIZE]] %[[R]]
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ptr.align_offset(32)
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}
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