mirror of https://github.com/rust-lang/rust
91 lines
2.9 KiB
Rust
91 lines
2.9 KiB
Rust
//@ compile-flags: -O
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//@ only-x86_64
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#![crate_type = "lib"]
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use std::mem::swap;
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use std::ptr::{read, copy_nonoverlapping, write};
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type KeccakBuffer = [[u64; 5]; 5];
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// A basic read+copy+write swap implementation ends up copying one of the values
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// to stack for large types, which is completely unnecessary as the lack of
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// overlap means we can just do whatever fits in registers at a time.
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// CHECK-LABEL: @swap_basic
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#[no_mangle]
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pub fn swap_basic(x: &mut KeccakBuffer, y: &mut KeccakBuffer) {
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// CHECK: alloca [200 x i8]
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// SAFETY: exclusive references are always valid to read/write,
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// are non-overlapping, and nothing here panics so it's drop-safe.
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unsafe {
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let z = read(x);
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copy_nonoverlapping(y, x, 1);
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write(y, z);
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}
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}
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// This test verifies that the library does something smarter, and thus
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// doesn't need any scratch space on the stack.
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// CHECK-LABEL: @swap_std
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#[no_mangle]
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pub fn swap_std(x: &mut KeccakBuffer, y: &mut KeccakBuffer) {
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// CHECK-NOT: alloca
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// CHECK: load <{{[0-9]+}} x i64>
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// CHECK: store <{{[0-9]+}} x i64>
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swap(x, y)
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}
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// Verify that types with usize alignment are swapped via vectored usizes,
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// not falling back to byte-level code.
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// CHECK-LABEL: @swap_slice
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#[no_mangle]
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pub fn swap_slice(x: &mut [KeccakBuffer], y: &mut [KeccakBuffer]) {
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// CHECK-NOT: alloca
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// CHECK: load <{{[0-9]+}} x i64>
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// CHECK: store <{{[0-9]+}} x i64>
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if x.len() == y.len() {
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x.swap_with_slice(y);
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}
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}
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// But for a large align-1 type, vectorized byte copying is what we want.
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type OneKilobyteBuffer = [u8; 1024];
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// CHECK-LABEL: @swap_1kb_slices
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#[no_mangle]
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pub fn swap_1kb_slices(x: &mut [OneKilobyteBuffer], y: &mut [OneKilobyteBuffer]) {
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// CHECK-NOT: alloca
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// CHECK: load <{{[0-9]+}} x i8>
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// CHECK: store <{{[0-9]+}} x i8>
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if x.len() == y.len() {
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x.swap_with_slice(y);
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}
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}
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// This verifies that the 2×read + 2×write optimizes to just 3 memcpys
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// for an unusual type like this. It's not clear whether we should do anything
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// smarter in Rust for these, so for now it's fine to leave these up to the backend.
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// That's not as bad as it might seem, as for example, LLVM will lower the
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// memcpys below to VMOVAPS on YMMs if one enables the AVX target feature.
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// Eventually we'll be able to pass `align_of::<T>` to a const generic and
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// thus pick a smarter chunk size ourselves without huge code duplication.
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#[repr(align(64))]
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pub struct BigButHighlyAligned([u8; 64 * 3]);
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// CHECK-LABEL: @swap_big_aligned
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#[no_mangle]
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pub fn swap_big_aligned(x: &mut BigButHighlyAligned, y: &mut BigButHighlyAligned) {
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}(ptr noundef nonnull align 64 dereferenceable(192)
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// CHECK: call void @llvm.memcpy.{{.+}}(ptr noundef nonnull align 64 dereferenceable(192)
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// CHECK: call void @llvm.memcpy.{{.+}}(ptr noundef nonnull align 64 dereferenceable(192)
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// CHECK-NOT: call void @llvm.memcpy
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swap(x, y)
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}
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