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Auto merge of #123886 - scottmcm:more-rvalue-operands, r=matthewjasper
Avoid `alloca`s in codegen for simple `mir::Aggregate` statements
The core idea here is to remove the abstraction penalty of simple newtypes in codegen.
Even something simple like constructing a
```rust
#[repr(transparent)] struct Foo(u32);
```
forces an `alloca` to be generated in nightly right now.
Certainly LLVM can optimize that away, but it would be nice if it didn't have to.
Quick example:
```rust
#[repr(transparent)]
pub struct Transparent32(u32);
#[no_mangle]
pub fn make_transparent(x: u32) -> Transparent32 {
let a = Transparent32(x);
a
}
```
on nightly we produce <https://rust.godbolt.org/z/zcvoM79ae>
```llvm
define noundef i32 `@make_transparent(i32` noundef %x) unnamed_addr #0 {
%a = alloca i32, align 4
store i32 %x, ptr %a, align 4
%0 = load i32, ptr %a, align 4, !noundef !3
ret i32 %0
}
```
but after this PR we produce
```llvm
define noundef i32 `@make_transparent(i32` noundef %x) unnamed_addr #0 {
start:
ret i32 %x
}
```
(even before the optimizer runs).- Loading branch information
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,123 @@ | ||
| //@ compile-flags: -O -C no-prepopulate-passes -Z randomize-layout=no | ||
|
|
||
| #![crate_type = "lib"] | ||
|
|
||
| #[repr(transparent)] | ||
| pub struct Transparent32(u32); | ||
|
|
||
| // CHECK: i32 @make_transparent(i32 noundef %x) | ||
| #[no_mangle] | ||
| pub fn make_transparent(x: u32) -> Transparent32 { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: ret i32 %x | ||
| let a = Transparent32(x); | ||
| a | ||
| } | ||
|
|
||
| // CHECK: i32 @make_closure(i32 noundef %x) | ||
| #[no_mangle] | ||
| pub fn make_closure(x: i32) -> impl Fn(i32) -> i32 { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: ret i32 %x | ||
| move |y| x + y | ||
| } | ||
|
|
||
| #[repr(transparent)] | ||
| pub struct TransparentPair((), (u16, u16), ()); | ||
|
|
||
| // CHECK: { i16, i16 } @make_transparent_pair(i16 noundef %x.0, i16 noundef %x.1) | ||
| #[no_mangle] | ||
| pub fn make_transparent_pair(x: (u16, u16)) -> TransparentPair { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i16, i16 } poison, i16 %x.0, 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i16, i16 } %[[TEMP0]], i16 %x.1, 1 | ||
| // CHECK: ret { i16, i16 } %[[TEMP1]] | ||
| let a = TransparentPair((), x, ()); | ||
| a | ||
| } | ||
|
|
||
| // CHECK-LABEL: { i32, i32 } @make_2_tuple(i32 noundef %x) | ||
| #[no_mangle] | ||
| pub fn make_2_tuple(x: u32) -> (u32, u32) { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i32, i32 } poison, i32 %x, 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i32, i32 } %[[TEMP0]], i32 %x, 1 | ||
| // CHECK: ret { i32, i32 } %[[TEMP1]] | ||
| let pair = (x, x); | ||
| pair | ||
| } | ||
|
|
||
| // CHECK-LABEL: i8 @make_cell_of_bool(i1 noundef zeroext %b) | ||
| #[no_mangle] | ||
| pub fn make_cell_of_bool(b: bool) -> std::cell::Cell<bool> { | ||
| // CHECK: %[[BYTE:.+]] = zext i1 %b to i8 | ||
| // CHECK: ret i8 %[[BYTE]] | ||
| std::cell::Cell::new(b) | ||
| } | ||
|
|
||
| // CHECK-LABLE: { i8, i16 } @make_cell_of_bool_and_short(i1 noundef zeroext %b, i16 noundef %s) | ||
| #[no_mangle] | ||
| pub fn make_cell_of_bool_and_short(b: bool, s: u16) -> std::cell::Cell<(bool, u16)> { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[BYTE:.+]] = zext i1 %b to i8 | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i8, i16 } poison, i8 %[[BYTE]], 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i8, i16 } %[[TEMP0]], i16 %s, 1 | ||
| // CHECK: ret { i8, i16 } %[[TEMP1]] | ||
| std::cell::Cell::new((b, s)) | ||
| } | ||
|
|
||
| // CHECK-LABEL: { i1, i1 } @make_tuple_of_bools(i1 noundef zeroext %a, i1 noundef zeroext %b) | ||
| #[no_mangle] | ||
| pub fn make_tuple_of_bools(a: bool, b: bool) -> (bool, bool) { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i1, i1 } poison, i1 %a, 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i1, i1 } %[[TEMP0]], i1 %b, 1 | ||
| // CHECK: ret { i1, i1 } %[[TEMP1]] | ||
| (a, b) | ||
| } | ||
|
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||
| pub struct Struct0(); | ||
|
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||
| // CHECK-LABEL: void @make_struct_0() | ||
| #[no_mangle] | ||
| pub fn make_struct_0() -> Struct0 { | ||
| // CHECK: ret void | ||
| let s = Struct0(); | ||
| s | ||
| } | ||
|
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||
| pub struct Struct1(i32); | ||
|
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| // CHECK-LABEL: i32 @make_struct_1(i32 noundef %a) | ||
| #[no_mangle] | ||
| pub fn make_struct_1(a: i32) -> Struct1 { | ||
| // CHECK: ret i32 %a | ||
| let s = Struct1(a); | ||
| s | ||
| } | ||
|
|
||
| pub struct Struct2Asc(i16, i64); | ||
|
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| // CHECK-LABEL: { i64, i16 } @make_struct_2_asc(i16 noundef %a, i64 noundef %b) | ||
| #[no_mangle] | ||
| pub fn make_struct_2_asc(a: i16, b: i64) -> Struct2Asc { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i64, i16 } poison, i64 %b, 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i64, i16 } %[[TEMP0]], i16 %a, 1 | ||
| // CHECK: ret { i64, i16 } %[[TEMP1]] | ||
| let s = Struct2Asc(a, b); | ||
| s | ||
| } | ||
|
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||
| pub struct Struct2Desc(i64, i16); | ||
|
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| // CHECK-LABEL: { i64, i16 } @make_struct_2_desc(i64 noundef %a, i16 noundef %b) | ||
| #[no_mangle] | ||
| pub fn make_struct_2_desc(a: i64, b: i16) -> Struct2Desc { | ||
| // CHECK-NOT: alloca | ||
| // CHECK: %[[TEMP0:.+]] = insertvalue { i64, i16 } poison, i64 %a, 0 | ||
| // CHECK: %[[TEMP1:.+]] = insertvalue { i64, i16 } %[[TEMP0]], i16 %b, 1 | ||
| // CHECK: ret { i64, i16 } %[[TEMP1]] | ||
| let s = Struct2Desc(a, b); | ||
| s | ||
| } |