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Rollup merge of #93313 - tmiasko:uninhabited, r=tmandry

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Check if call return type is visibly uninhabited when building MIR

The main motivation behind the change is to expose information about diverging
calls to the generator transform and match the precision of drop range tracking
which already understands that call expressions with visibly uninhabited types
diverges.

This change should also accept strictly more programs than before. That is
programs that were previously rejected due to errors raised by control-flow
sensitive checks in a code that is no longer considered reachable.

Fixes #93161.
This commit is contained in:
Dylan DPC 2022-04-20 18:26:01 +02:00 • committed by GitHub
commit 38e3f523c0
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19 changed files with 167 additions and 98 deletions
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13
compiler/rustc_mir_build/src/build/expr/into.rs
View file

@ -255,10 +255,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
func: fun,
args,
cleanup: None,
// FIXME(varkor): replace this with an uninhabitedness-based check.
// This requires getting access to the current module to call
// `tcx.is_ty_uninhabited_from`, which is currently tricky to do.
destination: if expr.ty.is_never() {
// The presence or absence of a return edge affects control-flow sensitive
// MIR checks and ultimately whether code is accepted or not. We can only
// omit the return edge if a return type is visibly uninhabited to a module
// that makes the call.
destination: if this.tcx.is_ty_uninhabited_from(
this.parent_module,
expr.ty,
this.param_env,
) {
None
} else {
Some((destination, success))

5
compiler/rustc_mir_build/src/build/mod.rs
View file

@ -350,6 +350,7 @@ struct Builder<'a, 'tcx> {
def_id: DefId,
hir_id: hir::HirId,
parent_module: DefId,
check_overflow: bool,
fn_span: Span,
arg_count: usize,
@ -807,15 +808,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
);
let lint_level = LintLevel::Explicit(hir_id);
let param_env = tcx.param_env(def.did);
let mut builder = Builder {
thir,
tcx,
infcx,
typeck_results: tcx.typeck_opt_const_arg(def),
region_scope_tree: tcx.region_scope_tree(def.did),
param_env: tcx.param_env(def.did),
param_env,
def_id: def.did.to_def_id(),
hir_id,
parent_module: tcx.parent_module(hir_id).to_def_id(),
check_overflow,
cfg: CFG { basic_blocks: IndexVec::new() },
fn_span: span,