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use crate::{
constant::{Constant, ConstantValue},
context::Context,
error::IrError,
function::Function,
instruction::Instruction,
value::ValueDatum,
AnalysisResults, BranchToWithArgs, Pass, PassMutability, Predicate, ScopedPass,
};
pub const CONSTCOMBINE_NAME: &str = "constcombine";
pub fn create_const_combine_pass() -> Pass {
Pass {
name: CONSTCOMBINE_NAME,
descr: "constant folding.",
deps: vec![],
runner: ScopedPass::FunctionPass(PassMutability::Transform(combine_constants)),
}
}
pub fn combine_constants(
context: &mut Context,
_: &AnalysisResults,
function: Function,
) -> Result<bool, IrError> {
let mut modified = false;
loop {
if combine_cmp(context, &function) {
modified = true;
continue;
}
if combine_cbr(context, &function)? {
modified = true;
continue;
}
break;
}
Ok(modified)
}
fn combine_cbr(context: &mut Context, function: &Function) -> Result<bool, IrError> {
let candidate = function
.instruction_iter(context)
.find_map(
|(in_block, inst_val)| match &context.values[inst_val.0].value {
ValueDatum::Instruction(Instruction::ConditionalBranch {
cond_value,
true_block,
false_block,
}) if cond_value.is_constant(context) => {
match &cond_value.get_constant(context).unwrap().value {
ConstantValue::Bool(true) => Some(Ok((
inst_val,
in_block,
true_block.clone(),
false_block.clone(),
))),
ConstantValue::Bool(false) => Some(Ok((
inst_val,
in_block,
false_block.clone(),
true_block.clone(),
))),
_ => Some(Err(IrError::VerifyConditionExprNotABool)),
}
}
_ => None,
},
)
.transpose()?;
candidate.map_or(
Ok(false),
|(
cbr,
from_block,
dest,
BranchToWithArgs {
block: no_more_dest,
..
},
)| {
no_more_dest.remove_pred(context, &from_block);
cbr.replace(context, ValueDatum::Instruction(Instruction::Branch(dest)));
Ok(true)
},
)
}
fn combine_cmp(context: &mut Context, function: &Function) -> bool {
let candidate = function
.instruction_iter(context)
.find_map(
|(block, inst_val)| match &context.values[inst_val.0].value {
ValueDatum::Instruction(Instruction::Cmp(pred, val1, val2))
if val1.is_constant(context) && val2.is_constant(context) =>
{
let val1 = val1.get_constant(context).unwrap();
let val2 = val2.get_constant(context).unwrap();
match pred {
Predicate::Equal => {
Some((inst_val, block, val1.eq(context, val2)))
}
Predicate::GreaterThan => {
let (ConstantValue::Uint(val1), ConstantValue::Uint(val2)) = (&val1.value, &val2.value)
else {
unreachable!("Type checker allowed non integer value for GreaterThan")
};
Some((inst_val, block, val1 > val2))
}
Predicate::LessThan => {
let (ConstantValue::Uint(val1), ConstantValue::Uint(val2)) = (&val1.value, &val2.value)
else {
unreachable!("Type checker allowed non integer value for LessThan")
};
Some((inst_val, block, val1 < val2))
}
}
}
_ => None,
},
);
candidate.map_or(false, |(inst_val, block, cn_replace)| {
inst_val.replace(
context,
ValueDatum::Constant(Constant::new_bool(context, cn_replace)),
);
block.remove_instruction(context, inst_val);
true
})
}