60 lines
2.3 KiB
Rust
60 lines
2.3 KiB
Rust
//! A pass that simplifies branches when their condition is known.
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use rustc::ty::TyCtxt;
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use rustc::mir::*;
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use crate::transform::{MirPass, MirSource};
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use std::borrow::Cow;
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pub struct SimplifyBranches { label: String }
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impl SimplifyBranches {
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pub fn new(label: &str) -> Self {
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SimplifyBranches { label: format!("SimplifyBranches-{}", label) }
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}
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}
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impl<'tcx> MirPass<'tcx> for SimplifyBranches {
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fn name(&self) -> Cow<'_, str> {
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Cow::Borrowed(&self.label)
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}
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fn run_pass(&self, tcx: TyCtxt<'tcx>, src: MirSource<'tcx>, body: &mut Body<'tcx>) {
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let param_env = tcx.param_env(src.def_id());
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for block in body.basic_blocks_mut() {
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let terminator = block.terminator_mut();
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terminator.kind = match terminator.kind {
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TerminatorKind::SwitchInt {
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discr: Operand::Constant(ref c), switch_ty, ref values, ref targets, ..
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} => {
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let constant = c.literal.try_eval_bits(tcx, param_env, switch_ty);
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if let Some(constant) = constant {
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let (otherwise, targets) = targets.split_last().unwrap();
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let mut ret = TerminatorKind::Goto { target: *otherwise };
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for (&v, t) in values.iter().zip(targets.iter()) {
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if v == constant {
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ret = TerminatorKind::Goto { target: *t };
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break;
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}
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}
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ret
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} else {
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continue
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}
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},
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TerminatorKind::Assert {
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target, cond: Operand::Constant(ref c), expected, ..
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} if (c.literal.try_eval_bool(tcx, param_env) == Some(true)) == expected =>
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TerminatorKind::Goto { target },
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TerminatorKind::FalseEdges { real_target, .. } => {
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TerminatorKind::Goto { target: real_target }
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},
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TerminatorKind::FalseUnwind { real_target, .. } => {
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TerminatorKind::Goto { target: real_target }
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},
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_ => continue
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};
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}
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}
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}
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