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+ how rust compiles
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+
+
+ the rust compilation model has surprising effects
+ +introduction to me
+
+
+
+
+
+ Noratrieb (she/her)
+ contributing to the compiler since 2021
+ +
+ 
+
+
+ behind cargo build
+cargo vs rustc
+
+
+
+ $ cargo build
+ cargo
+
+
+ rustc (clap)
+ rustc (tokio)
+ rustc (tracing)
+ rustc (yourcrate)
+ so you want to compile a crate
+so you want to compile a crate
+source code:
+
+ #[no_mangle]
+ pub fn add(a: u8, b: u8) -> u8 {
+ a.wrapping_add(b)
+ }
+ so you want to compile a crate
+MIR
+
+ codegen units
+
+fn main() {}
+
+
+
+ %%{init: {'theme': 'dark', 'themeVariables': { 'darkMode': true, 'fontSize': '25px' }}}%%
+ flowchart LR
+ mainmir["main (MIR)"]
+
+ subgraph mycgu1[my CGU 1]
+ mainll["main (LLVM IR)"]
+ end
+
+ mycgu1 --> mycgu1.rcgu.o
+
+ mainmir --> mainll
+
+ mycgu1.rcgu.o --> my_binary
+ std["std (and others)"] --> my_binary
+
+ codegen units (but more)
+
+fn main() {}
+fn foo1() {}
+fn foo2() {}
+
+
+
+ %%{init: {'theme': 'dark', 'themeVariables': { 'darkMode': true, 'fontSize': '25px' }}}%%
+ flowchart LR
+ mainmir["main (MIR)"]
+ foo1mir["foo1 (MIR)"]
+ foo2mir["foo2 (MIR)"]
+
+ subgraph mycgu1[my CGU 1]
+ mainll["main (LLVM IR)"]
+ end
+ subgraph mycgu2[my CGU 2]
+ foo1ll["foo1 (LLVM IR)"]
+ foo2ll["foo2 (LLVM IR)"]
+ end
+
+ mycgu1 --> mycgu1.rcgu.o
+ mycgu2 --> mycgu2.rcgu.o
+
+ mainmir --> mainll
+ foo1mir --> foo1ll
+ foo2mir --> foo2ll
+
+ mycgu1.rcgu.o --> my_binary
+ mycgu2.rcgu.o --> my_binary
+ std["std (and others)"] --> my_binary
+
+ codegen units (cross-crate)
+
+
+
+fn add() {}
+
+fn main() { math::add() }
+
+
+
+ %%{init: {'theme': 'dark', 'themeVariables': { 'darkMode': true, 'fontSize': '25px' }}}%%
+ flowchart LR
+ subgraph crate math
+ addmir["add (MIR)"]
+
+ subgraph mathcgu1[math CGU 1]
+ addll["add (LLVM IR)"]
+ end
+
+ addmir --> addll
+
+ mathcgu1 --> mathcgu1.rcgu.o
+
+ mathcgu1.rcgu.o --> libmath.rlib
+ end
+
+ subgraph my crate
+ mainmir["main (MIR)"]
+
+ subgraph mycgu1[my CGU 1]
+ mainll["main (LLVM IR)"]
+ end
+
+ mycgu1 --> mycgu1.rcgu.o
+
+ mainmir --> mainll
+
+ mycgu1.rcgu.o --> my_binary
+ libmath.rlib --> my_binary
+ std["std (and others)"] --> my_binary
+ end
+
+ instantiating generics
+
+ fn add<T: Add>(a: T, b: T) -> T::Output { a + b }
+ fn main() {
+ add(0_u16, 0_u16);
+ add(0_u32, 0_u32);
+ }
+
+
+
+ %%{init: {'theme': 'dark', 'themeVariables': { 'darkMode': true, 'fontSize': '25px' }}}%%
+ flowchart LR
+ addmir["add (MIR)"]
+ useitmir["main (MIR)"]
+
+ subgraph mycgu1[my CGU 1]
+ addu16ll["add_u16 (LLVM IR)"]
+ addu32ll["add_u32 (LLVM IR)"]
+ useitll["main (LLVM IR)"]
+ end
+
+ mycgu1 --> mycgu1.rcgu.o
+
+ addmir -->|instantiate with T=u16| addu16ll
+ addmir -->|instantiate with T=u32| addu32ll
+ useitmir --> useitll
+
+ mycgu1.rcgu.o --> my_binary
+ std["std (and others)"] --> my_binary
+
+ generics (cross-crate)
+
+
+
+ pub fn add<T: Add>(a: T, b: T) -> T::Output {
+ a + b
+ }
+
+ fn main() {
+ add(0_u16, 0_u16);
+ add(0_u32, 0_u32);
+ }
+
+
+
+ %%{init: {'theme': 'dark', 'themeVariables': { 'darkMode': true, 'fontSize': '25px' }}}%%
+ flowchart LR
+ subgraph crate math
+ addmir["add (MIR)"]
+ end
+
+ subgraph my crate
+ mainmir["main (MIR)"]
+ end
+
+ subgraph my crate
+ subgraph mycgu1[my CGU 1]
+ addu16ll["add_u16 (LLVM IR)"]
+ addu32ll["add_u32 (LLVM IR)"]
+ mainll["main (LLVM IR)"]
+ end
+
+ mainmir --> mainll
+ addmir --> addu16ll
+ addmir --> addu32ll
+ mycgu1 --> mycgu1.rcgu.o
+ mycgu1.rcgu.o --> my_binary
+ std["std (and others)"] --> my_binary
+ end
+
+