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Update and improve rustc_codegen_{llvm,ssa} docs #80323

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Jan 1, 2021
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Update and improve rustc_codegen_{llvm,ssa} docs #80323

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18 changes: 8 additions & 10 deletions compiler/rustc_codegen_llvm/src/base.rs
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Original file line number Diff line number Diff line change
@@ -1,17 +1,15 @@
//! Codegen the completed AST to the LLVM IR.
//!
//! Some functions here, such as codegen_block and codegen_expr, return a value --
//! the result of the codegen to LLVM -- while others, such as codegen_fn
//! and mono_item, are called only for the side effect of adding a
//! particular definition to the LLVM IR output we're producing.
//! Codegen the MIR to the LLVM IR.
//!
//! Hopefully useful general knowledge about codegen:
//!
//! * There's no way to find out the `Ty` type of a Value. Doing so
//! * There's no way to find out the [`Ty`] type of a [`Value`]. Doing so
//! would be "trying to get the eggs out of an omelette" (credit:
//! pcwalton). You can, instead, find out its `llvm::Type` by calling `val_ty`,
//! but one `llvm::Type` corresponds to many `Ty`s; for instance, `tup(int, int,
//! int)` and `rec(x=int, y=int, z=int)` will have the same `llvm::Type`.
//! pcwalton). You can, instead, find out its [`llvm::Type`] by calling [`val_ty`],
//! but one [`llvm::Type`] corresponds to many [`Ty`]s; for instance, `tup(int, int,
//! int)` and `rec(x=int, y=int, z=int)` will have the same [`llvm::Type`].
//!
//! [`Ty`]: rustc_middle::ty::Ty
//! [`val_ty`]: common::val_ty

use super::ModuleLlvm;

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1 change: 1 addition & 0 deletions compiler/rustc_codegen_llvm/src/common.rs
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Expand Up @@ -314,6 +314,7 @@ impl ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
}
}

/// Get the [LLVM type][Type] of a [`Value`].
pub fn val_ty(v: &Value) -> &Type {
unsafe { llvm::LLVMTypeOf(v) }
}
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15 changes: 0 additions & 15 deletions compiler/rustc_codegen_ssa/src/base.rs
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@@ -1,18 +1,3 @@
//! Codegen the completed AST to the LLVM IR.
//!
//! Some functions here, such as `codegen_block` and `codegen_expr`, return a value --
//! the result of the codegen to LLVM -- while others, such as `codegen_fn`
//! and `mono_item`, are called only for the side effect of adding a
//! particular definition to the LLVM IR output we're producing.
//!
//! Hopefully useful general knowledge about codegen:
//!
//! * There's no way to find out the `Ty` type of a `Value`. Doing so
//! would be "trying to get the eggs out of an omelette" (credit:
//! pcwalton). You can, instead, find out its `llvm::Type` by calling `val_ty`,
//! but one `llvm::Type` corresponds to many `Ty`s; for instance, `tup(int, int,
//! int)` and `rec(x=int, y=int, z=int)` will have the same `llvm::Type`.
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Wow, I was just looking through what rustc looked like many years ago, and noticed that this comment was originally introduced 10 years ago (!!) in dba9cae as:

//   * There's no way to find out the ty::t type of a ValueRef.  Doing so
//     would be "trying to get the eggs out of an omelette" (credit:
//     pcwalton).  You can, instead, find out its TypeRef by calling val_ty,
//     but many TypeRefs correspond to one ty::t; for instance, tup(int, int,
//     int) and rec(x=int, y=int, z=int) will have the same TypeRef.

Quite some software archaeology there!


use crate::back::write::{
compute_per_cgu_lto_type, start_async_codegen, submit_codegened_module_to_llvm,
submit_post_lto_module_to_llvm, submit_pre_lto_module_to_llvm, ComputedLtoType, OngoingCodegen,
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