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Auto merge of #81327 - RalfJung:codegen-no-const-fail, r=oli-obk

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codegen: assume constants cannot fail to evaluate

https://github.com/rust-lang/rust/pull/80579 landed, so we can finally remove this old hack from codegen and instead assume that consts never fail to evaluate. :)

r? `@oli-obk`
This commit is contained in:
bors 2021-01-31 07:03:09 +00:00
commit 9b32429822
4 changed files with 21 additions and 21 deletions
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5
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -626,6 +626,11 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
total_codegen_time += start_time.elapsed();
module
};
// This will unwind if there are errors, which triggers our `AbortCodegenOnDrop`
// guard. Unfortunately, just skipping the `submit_codegened_module_to_llvm` makes
// compilation hang on post-monomorphization errors.
tcx.sess.abort_if_errors();
submit_codegened_module_to_llvm(
&backend,
&ongoing_codegen.coordinator_send,

8
compiler/rustc_codegen_ssa/src/mir/mod.rs
View File

@ -188,8 +188,11 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut bx);
// Evaluate all required consts; codegen later assumes that CTFE will never fail.
let mut all_consts_ok = true;
for const_ in &mir.required_consts {
if let Err(err) = fx.eval_mir_constant(const_) {
all_consts_ok = false;
match err {
// errored or at least linted
ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
@ -199,6 +202,11 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}
}
}
if !all_consts_ok {
// We leave the IR in some half-built state here, and rely on this code not even being
// submitted to LLVM once an error was raised.
return;
}
let memory_locals = analyze::non_ssa_locals(&fx);

25
compiler/rustc_codegen_ssa/src/mir/operand.rs
View File

@ -6,9 +6,8 @@ use crate::glue;
use crate::traits::*;
use crate::MemFlags;
use rustc_errors::ErrorReported;
use rustc_middle::mir;
use rustc_middle::mir::interpret::{ConstValue, ErrorHandled, Pointer, Scalar};
use rustc_middle::mir::interpret::{ConstValue, Pointer, Scalar};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::Ty;
use rustc_target::abi::{Abi, Align, LayoutOf, Size};
@ -439,25 +438,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
mir::Operand::Constant(ref constant) => {
self.eval_mir_constant_to_operand(bx, constant).unwrap_or_else(|err| {
match err {
// errored or at least linted
ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {}
ErrorHandled::TooGeneric => {
bug!("codegen encountered polymorphic constant")
}
}
// Allow RalfJ to sleep soundly knowing that even refactorings that remove
// the above error (or silence it under some conditions) will not cause UB.
bx.abort();
// We still have to return an operand but it doesn't matter,
// this code is unreachable.
let ty = self.monomorphize(constant.literal.ty);
let layout = bx.cx().layout_of(ty);
bx.load_operand(PlaceRef::new_sized(
bx.cx().const_undef(bx.cx().type_ptr_to(bx.cx().backend_type(layout))),
layout,
))
// This cannot fail because we checked all required_consts in advance.
self.eval_mir_constant_to_operand(bx, constant).unwrap_or_else(|_err| {
span_bug!(constant.span, "erroneous constant not captured by required_consts")
})
}
}

4
compiler/rustc_mir/src/interpret/operand.rs
View File

@ -511,6 +511,10 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
Constant(ref constant) => {
let val =
self.subst_from_current_frame_and_normalize_erasing_regions(constant.literal);
// This can still fail:
// * During ConstProp, with `TooGeneric` or since the `requried_consts` were not all
// checked yet.
// * During CTFE, since promoteds in `const`/`static` initializer bodies can fail.
self.const_to_op(val, layout)?
}
};