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Add comments to branch folding and reordering functions in simple_preopt.

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This commit is contained in:
Tyler McMullen
2019-01-03 11:56:36 -08:00
committed by Benjamin Bouvier
parent fd6940baaf
commit 402d0d9c83
1 changed files with 10 additions and 0 deletions
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10
cranelift/codegen/src/simple_preopt.rs
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@@ -555,6 +555,11 @@ enum BranchOptKind {
NotEqualZero,
}
/// Fold comparisons into branch operations when possible.
///
/// This matches against operations which compare against zero, then use the
/// result in a `brz` or `brnz` branch. It folds those two operations into a
/// single `brz` or `brnz`.
fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
let info = match pos.func.dfg[inst] {
InstructionData::Branch {
@@ -648,6 +653,11 @@ enum BranchOrderKind {
InvertIcmpCond(IntCC, Value, Value),
}
/// Reorder branches to encourage fallthroughs.
///
/// When an ebb ends with a conditional branch followed by an unconditional
/// branch, this will reorder them if one of them is branching to the next Ebb
/// layout-wise. The unconditional jump can then become a fallthrough.
fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, ebb: Ebb, inst: Inst) {
let info = match pos.func.dfg[inst] {
InstructionData::Jump {