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Rollup merge of #58324 - RalfJung:fn-ptr-eq, r=oli-obk

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miri: give non-generic functions a stable address

This makes Miri correctly handle format string parameters despite https://github.com/rust-lang/rust/issues/58320.

Matching Miri PR: https://github.com/solson/miri/pull/626

r? @oli-obk
This commit is contained in:
Guillaume Gomez 2019-02-10 21:45:20 +01:00 committed by GitHub
commit a09aa0fde1
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1 changed files with 23 additions and 8 deletions
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31
src/librustc/mir/interpret/mod.rs
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@ -27,7 +27,7 @@ pub use self::pointer::{Pointer, PointerArithmetic};
use std::fmt;
use crate::mir;
use crate::hir::def_id::DefId;
use crate::ty::{self, TyCtxt, Instance};
use crate::ty::{self, TyCtxt, Instance, subst::UnpackedKind};
use crate::ty::layout::{self, Size};
use std::io;
use crate::rustc_serialize::{Encoder, Decodable, Encodable};
@ -318,14 +318,29 @@ impl<'tcx> AllocMap<'tcx> {
id
}
/// Functions cannot be identified by pointers, as asm-equal functions can get deduplicated
/// by the linker and functions can be duplicated across crates.
/// We thus generate a new `AllocId` for every mention of a function. This means that
/// `main as fn() == main as fn()` is false, while `let x = main as fn(); x == x` is true.
pub fn create_fn_alloc(&mut self, instance: Instance<'tcx>) -> AllocId {
let id = self.reserve();
self.id_to_kind.insert(id, AllocKind::Function(instance));
id
// Functions cannot be identified by pointers, as asm-equal functions can get deduplicated
// by the linker (we set the "unnamed_addr" attribute for LLVM) and functions can be
// duplicated across crates.
// We thus generate a new `AllocId` for every mention of a function. This means that
// `main as fn() == main as fn()` is false, while `let x = main as fn(); x == x` is true.
// However, formatting code relies on function identity (see #58320), so we only do
// this for generic functions. Lifetime parameters are ignored.
let is_generic = instance.substs.into_iter().any(|kind| {
match kind.unpack() {
UnpackedKind::Lifetime(_) => false,
_ => true,
}
});
if is_generic {
// Get a fresh ID
let id = self.reserve();
self.id_to_kind.insert(id, AllocKind::Function(instance));
id
} else {
// Deduplicate
self.intern(AllocKind::Function(instance))
}
}
/// Returns `None` in case the `AllocId` is dangling. An `EvalContext` can still have a