mirror of https://github.com/rust-lang/rust
34 lines
1.4 KiB
Rust
34 lines
1.4 KiB
Rust
// This test ensures that `mem::replace::<T>` only ever calls `@llvm.memcpy`
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// with `size_of::<T>()` as the size, and never goes through any wrapper that
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// may e.g. multiply `size_of::<T>()` with a variable "count" (which is only
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// known to be `1` after inlining).
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//@ compile-flags: -C no-prepopulate-passes -Zinline-mir=no
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//@ ignore-debug: precondition checks in ptr::read make them a bad candidate for MIR inlining
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#![crate_type = "lib"]
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#[repr(C, align(8))]
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pub struct Big([u64; 7]);
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pub fn replace_big(dst: &mut Big, src: Big) -> Big {
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// Back in 1.68, this emitted six `memcpy`s.
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// `read_via_copy` in 1.69 got that down to three.
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// `write_via_move` and nvro get this down to the essential two.
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std::mem::replace(dst, src)
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}
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// NOTE(eddyb) the `CHECK-NOT`s ensure that the only calls of `@llvm.memcpy` in
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// the entire output, are the direct calls we want, from `ptr::replace`.
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// CHECK-NOT: call void @llvm.memcpy
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// For a large type, we expect exactly three `memcpy`s
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// CHECK-LABEL: define internal void @{{.+}}mem{{.+}}replace{{.+}}sret([56 x i8])
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}(ptr align 8 %result, ptr align 8 %dest, i{{.*}} 56, i1 false)
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}(ptr align 8 %dest, ptr align 8 %src, i{{.*}} 56, i1 false)
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK-NOT: call void @llvm.memcpy
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