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-Zmir-enable-passes: document that this may enable unsound passes #116595

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Oct 10, 2023
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-Zmir-enable-passes: document that this may enable unsound passes #116595

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-Zmir-enable-passes: document that this may enable unsound passes
RalfJung Oct 10, 2023
d805b26
add some comments explaining why MIR opts are marked as unsound
RalfJung Oct 10, 2023
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1 change: 1 addition & 0 deletions compiler/rustc_mir_transform/src/early_otherwise_branch.rs
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Expand Up @@ -95,6 +95,7 @@ pub struct EarlyOtherwiseBranch;

impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
// unsound: https://github.com/rust-lang/rust/issues/95162
sess.mir_opt_level() >= 3 && sess.opts.unstable_opts.unsound_mir_opts
}

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3 changes: 3 additions & 0 deletions compiler/rustc_mir_transform/src/large_enums.rs
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Expand Up @@ -30,6 +30,9 @@ pub struct EnumSizeOpt {

impl<'tcx> MirPass<'tcx> for EnumSizeOpt {
fn is_enabled(&self, sess: &Session) -> bool {
// There are some differences in behavior on wasm and ARM that are not properly
// understood, so we conservatively treat this optimization as unsound:
// https://github.com/rust-lang/rust/pull/85158#issuecomment-1101836457
sess.opts.unstable_opts.unsound_mir_opts || sess.mir_opt_level() >= 3
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
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2 changes: 1 addition & 1 deletion compiler/rustc_mir_transform/src/nrvo.rs
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Expand Up @@ -34,7 +34,7 @@ pub struct RenameReturnPlace;

impl<'tcx> MirPass<'tcx> for RenameReturnPlace {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
// #111005
// unsound: #111005
sess.mir_opt_level() > 0 && sess.opts.unstable_opts.unsound_mir_opts
}

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7 changes: 4 additions & 3 deletions compiler/rustc_session/src/options.rs
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Expand Up @@ -1610,9 +1610,10 @@ options! {
"emit Retagging MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
(default: no)"),
mir_enable_passes: Vec<(String, bool)> = (Vec::new(), parse_list_with_polarity, [TRACKED],
"use like `-Zmir-enable-passes=+DestinationPropagation,-InstSimplify`. Forces the specified passes to be \
enabled, overriding all other checks. Passes that are not specified are enabled or \
disabled by other flags as usual."),
"use like `-Zmir-enable-passes=+DestinationPropagation,-InstSimplify`. Forces the \
specified passes to be enabled, overriding all other checks. In particular, this will \
enable unsound (known-buggy and hence usually disabled) passes without further warning! \
Passes that are not specified are enabled or disabled by other flags as usual."),
mir_include_spans: bool = (false, parse_bool, [UNTRACKED],
"use line numbers relative to the function in mir pretty printing"),
mir_keep_place_mention: bool = (false, parse_bool, [TRACKED],
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