Add branch order optimization to simple_preopt to encourage fallthroughs.
This commit is contained in:
Tyler McMullen
committed by
Benjamin Bouvier
Benjamin Bouvier
parent
57f087c9da
commit
947130be81
@@ -9,7 +9,7 @@
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use crate::cursor::{Cursor, FuncCursor};
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use crate::divconst_magic_numbers::{magic_s32, magic_s64, magic_u32, magic_u64};
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use crate::divconst_magic_numbers::{MS32, MS64, MU32, MU64};
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use crate::ir::condcodes::IntCC;
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use crate::ir::condcodes::{CondCode, FloatCC, IntCC};
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use crate::ir::dfg::ValueDef;
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use crate::ir::instructions::{Opcode, ValueList};
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use crate::ir::types::{I32, I64};
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@@ -623,11 +623,197 @@ fn branch_opt(pos: &mut FuncCursor, inst: Inst) {
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}
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}
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struct BranchOrderInfo {
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term_inst: Inst,
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term_inst_args: ValueList,
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term_dest: Ebb,
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cond_inst: Inst,
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cond_arg: Value,
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cond_inst_args: ValueList,
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cond_dest: Ebb,
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kind: BranchOrderKind,
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}
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enum BranchOrderKind {
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BrzToBrnz,
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BrnzToBrz,
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InvertIntCond(IntCC),
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InvertFloatCond(FloatCC),
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}
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fn branch_order(pos: &mut FuncCursor, cfg: &mut ControlFlowGraph, ebb: Ebb, inst: Inst) {
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let info = match pos.func.dfg[inst] {
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InstructionData::Jump {
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opcode: Opcode::Jump,
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destination,
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ref args,
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} => {
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if let Some(next_ebb) = pos.func.layout.next_ebb(ebb) {
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if destination == next_ebb {
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return;
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}
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if let Some(prev_inst) = pos.func.layout.prev_inst(inst) {
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let prev_inst_data = &pos.func.dfg[prev_inst];
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if !prev_inst_data.opcode().is_branch() {
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return;
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}
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if let Some(prev_dest) = prev_inst_data.branch_destination() {
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if prev_dest != next_ebb {
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return;
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}
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match prev_inst_data {
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InstructionData::Branch {
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opcode,
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args: ref prev_args,
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destination: cond_dest,
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..
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} => {
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let cond_arg = {
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let args = pos.func.dfg.inst_args(prev_inst);
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args[0]
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};
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match opcode {
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Opcode::Brz => BranchOrderInfo {
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term_inst: inst,
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term_inst_args: args.clone(),
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term_dest: destination,
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cond_inst: prev_inst,
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cond_arg: cond_arg,
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cond_inst_args: prev_args.clone(),
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cond_dest: *cond_dest,
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kind: BranchOrderKind::BrzToBrnz,
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},
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Opcode::Brnz => BranchOrderInfo {
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term_inst: inst,
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term_inst_args: args.clone(),
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term_dest: destination,
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cond_inst: prev_inst,
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cond_arg: cond_arg,
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cond_inst_args: prev_args.clone(),
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cond_dest: *cond_dest,
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kind: BranchOrderKind::BrnzToBrz,
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},
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_ => panic!("unexpected opcode"),
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}
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}
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InstructionData::BranchInt {
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opcode: Opcode::Brif,
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args: ref prev_args,
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cond,
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destination: cond_dest,
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..
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} => {
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let cond_arg = {
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let args = pos.func.dfg.inst_args(prev_inst);
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args[0]
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};
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BranchOrderInfo {
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term_inst: inst,
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term_inst_args: args.clone(),
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term_dest: destination,
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cond_inst: prev_inst,
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cond_arg: cond_arg,
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cond_inst_args: prev_args.clone(),
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cond_dest: *cond_dest,
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kind: BranchOrderKind::InvertIntCond(*cond),
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}
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}
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InstructionData::BranchFloat {
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opcode: Opcode::Brff,
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args: ref prev_args,
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cond,
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destination: cond_dest,
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..
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} => {
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let cond_arg = {
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let args = pos.func.dfg.inst_args(prev_inst);
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args[0]
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};
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BranchOrderInfo {
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term_inst: inst,
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term_inst_args: args.clone(),
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term_dest: destination,
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cond_inst: prev_inst,
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cond_arg: cond_arg,
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cond_inst_args: prev_args.clone(),
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cond_dest: *cond_dest,
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kind: BranchOrderKind::InvertFloatCond(*cond),
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}
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}
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_ => return,
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}
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} else {
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return;
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}
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} else {
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return;
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}
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} else {
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return;
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}
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}
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_ => return,
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};
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let cond_args = {
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info.cond_inst_args
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.as_slice(&pos.func.dfg.value_lists)
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.to_vec()
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};
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let term_args = {
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info.term_inst_args
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.as_slice(&pos.func.dfg.value_lists)
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.to_vec()
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};
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pos.func
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.dfg
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.replace(info.term_inst)
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.fallthrough(info.cond_dest, &cond_args[1..]);
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match info.kind {
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BranchOrderKind::BrnzToBrz => {
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pos.func
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.dfg
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.replace(info.cond_inst)
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.brz(info.cond_arg, info.term_dest, &term_args);
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}
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BranchOrderKind::BrzToBrnz => {
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pos.func
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.dfg
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.replace(info.cond_inst)
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.brnz(info.cond_arg, info.term_dest, &term_args);
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}
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BranchOrderKind::InvertIntCond(cond) => {
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pos.func.dfg.replace(info.cond_inst).brif(
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cond.inverse(),
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info.cond_arg,
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info.term_dest,
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&term_args,
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);
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}
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BranchOrderKind::InvertFloatCond(cond) => {
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pos.func.dfg.replace(info.cond_inst).brff(
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cond.inverse(),
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info.cond_arg,
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info.term_dest,
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&term_args,
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);
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}
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}
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cfg.recompute_ebb(pos.func, ebb);
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}
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/// The main pre-opt pass.
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pub fn do_preopt(func: &mut Function) {
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pub fn do_preopt(func: &mut Function, cfg: &mut ControlFlowGraph) {
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let _tt = timing::preopt();
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let mut pos = FuncCursor::new(func);
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while let Some(_ebb) = pos.next_ebb() {
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while let Some(ebb) = pos.next_ebb() {
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while let Some(inst) = pos.next_inst() {
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// Apply basic simplifications.
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simplify(&mut pos, inst);
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@@ -643,6 +829,7 @@ pub fn do_preopt(func: &mut Function) {
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//-- END -- division by constants ------------------
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branch_opt(&mut pos, inst);
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branch_order(&mut pos, cfg, ebb, inst);
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}
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}
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}
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