b2c717fa33
I was looking into `array::IntoIter` optimization, and noticed that it wasn't annotating the loads with `noundef` for simple things like `array::IntoIter<i32, N>`. Turned out to be a more general problem as `MaybeUninit::assume_init_read` isn't marking the load as initialized (<https://rust.godbolt.org/z/Mxd8TPTnv>), which is unfortunate since that's basically its reason to exist. This PR lowers `ptr::read(p)` to `copy *p` in MIR, which fortuitiously also improves the IR we give to LLVM for things like `mem::replace`.
55 lines
2.2 KiB
Rust
55 lines
2.2 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: the debug assertions get in the way
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#![crate_type = "lib"]
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pub fn replace_byte(dst: &mut u8, src: u8) -> u8 {
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std::mem::replace(dst, src)
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}
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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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// Before the `read_via_copy` intrinsic, this emitted six `memcpy`s.
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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(%Big)
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// CHECK-NOT: alloca
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// CHECK: alloca %Big
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// CHECK-NOT: alloca
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false)
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, i{{.*}} 56, i1 false)
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 8 %{{.*}}, {{i8\*|ptr}} align 8 %{{.*}}, 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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// For a small type, we expect one each of `load`/`store`/`memcpy` instead
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// CHECK-LABEL: define internal noundef i8 @{{.+}}mem{{.+}}replace
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// CHECK-NOT: alloca
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// CHECK: alloca i8
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// CHECK-NOT: alloca
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: load i8
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: store i8
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// CHECK-NOT: call void @llvm.memcpy
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// CHECK: call void @llvm.memcpy.{{.+}}({{i8\*|ptr}} align 1 %{{.*}}, {{i8\*|ptr}} align 1 %{{.*}}, i{{.*}} 1, 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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