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Add branch order optimization to simple_preopt to encourage fallthroughs.

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This commit is contained in:
Tyler McMullen
2018-12-20 16:36:49 -08:00
committed by Benjamin Bouvier
parent 57f087c9da
commit 947130be81
2 changed files with 191 additions and 4 deletions
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2
cranelift/codegen/src/context.rs
View File

@@ -225,7 +225,7 @@ impl Context {
/// Perform pre-legalization rewrites on the function. /// Perform pre-legalization rewrites on the function.
pub fn preopt(&mut self, isa: &TargetIsa) -> CodegenResult<()> { pub fn preopt(&mut self, isa: &TargetIsa) -> CodegenResult<()> {
do_preopt(&mut self.func); do_preopt(&mut self.func, &mut self.cfg);
self.verify_if(isa)?; self.verify_if(isa)?;
Ok(()) Ok(())
} }

193
cranelift/codegen/src/simple_preopt.rs
View File

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