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Reimplement simplify_cfg for SwitchInt

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First example of optimisation that applies to many more cases than originally.
This commit is contained in:
Simonas Kazlauskas 2017-02-02 08:41:01 +02:00
parent 92c56f607b
commit 64182a587c
1 changed files with 18 additions and 14 deletions
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32
src/librustc_mir/transform/simplify_branches.rs
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@ -30,26 +30,30 @@ impl<'l, 'tcx> MirPass<'tcx> for SimplifyBranches<'l> {
for block in mir.basic_blocks_mut() {
let terminator = block.terminator_mut();
terminator.kind = match terminator.kind {
// TerminatorKind::If { ref targets, cond: Operand::Constant(Constant {
// literal: Literal::Value {
// value: ConstVal::Bool(cond)
// }, ..
// }) } => {
// if cond {
// TerminatorKind::Goto { target: targets.0 }
// } else {
// TerminatorKind::Goto { target: targets.1 }
// }
// }
TerminatorKind::SwitchInt { discr: Operand::Constant(Constant {
literal: Literal::Value { ref value }, ..
}), ref values, ref targets, .. } => {
if let Some(ref constint) = value.to_const_int() {
let (otherwise, targets) = targets.split_last().unwrap();
let mut ret = TerminatorKind::Goto { target: *otherwise };
for (v, t) in values.iter().zip(targets.iter()) {
if v == constint {
ret = TerminatorKind::Goto { target: *t };
break;
}
}
ret
} else {
continue
}
},
TerminatorKind::Assert { target, cond: Operand::Constant(Constant {
literal: Literal::Value {
value: ConstVal::Bool(cond)
}, ..
}), expected, .. } if cond == expected => {
TerminatorKind::Goto { target: target }
}
},
_ => continue
};
}