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Optimize branches when the target is statically known to a jump

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This can happen in generic code
This commit is contained in:
bjorn3 2020-12-09 19:55:11 +01:00
parent 5f21ff20b3
commit 994b91ac73
2 changed files with 56 additions and 7 deletions
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24
src/base.rs
View File

@ -307,7 +307,9 @@ fn codegen_fn_content(fx: &mut FunctionCx<'_, '_, impl Module>) {
} => {
let discr = codegen_operand(fx, discr).load_scalar(fx);
if switch_ty.kind() == fx.tcx.types.bool.kind() {
let use_bool_opt = switch_ty.kind() == fx.tcx.types.bool.kind()
|| (targets.iter().count() == 1 && targets.iter().next().unwrap().0 == 0);
if use_bool_opt {
assert_eq!(targets.iter().count(), 1);
let (then_value, then_block) = targets.iter().next().unwrap();
let then_block = fx.get_block(then_block);
@ -325,12 +327,22 @@ fn codegen_fn_content(fx: &mut FunctionCx<'_, '_, impl Module>) {
let discr = crate::optimize::peephole::maybe_unwrap_bint(&mut fx.bcx, discr);
let discr =
crate::optimize::peephole::make_branchable_value(&mut fx.bcx, discr);
if test_zero {
fx.bcx.ins().brz(discr, then_block, &[]);
fx.bcx.ins().jump(else_block, &[]);
if let Some(taken) = crate::optimize::peephole::maybe_known_branch_taken(
&fx.bcx, discr, test_zero,
) {
if taken {
fx.bcx.ins().jump(then_block, &[]);
} else {
fx.bcx.ins().jump(else_block, &[]);
}
} else {
fx.bcx.ins().brnz(discr, then_block, &[]);
fx.bcx.ins().jump(else_block, &[]);
if test_zero {
fx.bcx.ins().brz(discr, then_block, &[]);
fx.bcx.ins().jump(else_block, &[]);
} else {
fx.bcx.ins().brnz(discr, then_block, &[]);
fx.bcx.ins().jump(else_block, &[]);
}
}
} else {
let mut switch = ::cranelift_frontend::Switch::new();

39
src/optimize/peephole.rs
View File

@ -73,7 +73,7 @@ pub(crate) fn make_branchable_value(bcx: &mut FunctionBuilder<'_>, arg: Value) -
})()
.unwrap_or_else(|| {
match bcx.func.dfg.value_type(arg) {
types::I8 | types::I32 => {
types::I8 | types::I16 => {
// WORKAROUND for brz.i8 and brnz.i8 not yet being implemented
bcx.ins().uextend(types::I32, arg)
}
@ -81,3 +81,40 @@ pub(crate) fn make_branchable_value(bcx: &mut FunctionBuilder<'_>, arg: Value) -
}
})
}
/// Returns whether the branch is statically known to be taken or `None` if it isn't statically known.
pub(crate) fn maybe_known_branch_taken(
bcx: &FunctionBuilder<'_>,
arg: Value,
test_zero: bool,
) -> Option<bool> {
let arg_inst = if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
arg_inst
} else {
return None;
};
match bcx.func.dfg[arg_inst] {
InstructionData::UnaryBool {
opcode: Opcode::Bconst,
imm,
} => {
if test_zero {
Some(!imm)
} else {
Some(imm)
}
}
InstructionData::UnaryImm {
opcode: Opcode::Iconst,
imm,
} => {
if test_zero {
Some(imm.bits() == 0)
} else {
Some(imm.bits() != 0)
}
}
_ => None,
}
}