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Iteratively simplify const conditions #107702

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Iteratively simplify const conditions #107702

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56 changes: 35 additions & 21 deletions compiler/rustc_mir_transform/src/simplify_branches.rs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
use crate::dataflow_const_prop::DataflowConstProp;
use crate::MirPass;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
Expand All @@ -19,29 +20,42 @@ impl<'tcx> MirPass<'tcx> for SimplifyConstCondition {
}

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let param_env = tcx.param_env(body.source.def_id());
for block in body.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
TerminatorKind::SwitchInt {
discr: Operand::Constant(ref c), ref targets, ..
} => {
let constant = c.literal.try_eval_bits(tcx, param_env, c.ty());
if let Some(constant) = constant {
let target = targets.target_for_value(constant);
TerminatorKind::Goto { target }
} else {
continue;
loop {
let mut changed = false;
let param_env = tcx.param_env(body.source.def_id());
for block in body.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
TerminatorKind::SwitchInt {
discr: Operand::Constant(ref c),
ref targets,
..
} => {
let constant = c.literal.try_eval_bits(tcx, param_env, c.ty());
if let Some(constant) = constant {
changed = true;
let target = targets.target_for_value(constant);
TerminatorKind::Goto { target }
} else {
continue;
}
}
}
TerminatorKind::Assert {
target, cond: Operand::Constant(ref c), expected, ..
} => match c.literal.try_eval_bool(tcx, param_env) {
Some(v) if v == expected => TerminatorKind::Goto { target },
TerminatorKind::Assert {
target,
cond: Operand::Constant(ref c),
expected,
..
} => match c.literal.try_eval_bool(tcx, param_env) {
Some(v) if v == expected => {
changed = true;
TerminatorKind::Goto { target }
}
_ => continue,
},
_ => continue,
},
_ => continue,
};
};
}
if !changed { break } else { DataflowConstProp.run_pass(tcx, body) }
}
}
}