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Try normalizing types without RevealAll in ParamEnv in mir validation

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Before, the MIR validator used RevealAll in its ParamEnv for type
checking. This could cause false negatives in some cases due to
RevealAll ParamEnvs not always use all predicates as expected here.

Since some MIR passes like inlining use RevealAll as well, keep using
it in the MIR validator too, but when it fails usign RevealAll, also
try the check without it, to stop false negatives.
This commit is contained in:
Nilstrieb 2022-08-03 22:24:47 +02:00 • committed by nils
parent b96fa1a25c
commit 81a583c21e
2 changed files with 46 additions and 9 deletions
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30
compiler/rustc_const_eval/src/transform/validate.rs
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@ -181,16 +181,28 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
if (src, dest).has_opaque_types() {
return true;
}
// Normalize projections and things like that.
let param_env = self.param_env.with_reveal_all_normalized(self.tcx);
let src = self.tcx.normalize_erasing_regions(param_env, src);
let dest = self.tcx.normalize_erasing_regions(param_env, dest);
// Type-changing assignments can happen when subtyping is used. While
// all normal lifetimes are erased, higher-ranked types with their
// late-bound lifetimes are still around and can lead to type
// differences. So we compare ignoring lifetimes.
equal_up_to_regions(self.tcx, param_env, src, dest)
let try_equal_with_param_env = |param_env| {
let src = self.tcx.normalize_erasing_regions(param_env, src);
let dest = self.tcx.normalize_erasing_regions(param_env, dest);
// Type-changing assignments can happen when subtyping is used. While
// all normal lifetimes are erased, higher-ranked types with their
// late-bound lifetimes are still around and can lead to type
// differences. So we compare ignoring lifetimes.
equal_up_to_regions(self.tcx, param_env, src, dest)
};
// Normalize projections and things like that.
// First, try with reveal_all. This might not work in some cases, as the predicates
// can be cleared in reveal_all mode. We try the reveal first anyways as it is used
// by some other passes like inlining as well.
let param_env = self.param_env.with_reveal_all_normalized(self.tcx);
if try_equal_with_param_env(param_env) {
true
} else {
// If this fails, we can try it without the reveal.
try_equal_with_param_env(self.param_env)
}
}
}