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BE-270: HashQL: Optimize empty tuples to unit constants in MIR #8237

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Merged
indietyp merged 2 commits into from
Jan 19, 2026
Merged

BE-270: HashQL: Optimize empty tuples to unit constants in MIR #8237

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82bb150
feat: inst simplify
indietyp Jan 3, 2026
50abe89
test: simplification
indietyp Jan 3, 2026
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6 changes: 6 additions & 0 deletions libs/@local/hashql/mir/src/body/operand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,12 @@ impl<'heap> Operand<'heap> {
}
}

impl From<!> for Operand<'_> {
fn from(value: !) -> Self {
value
}
}

impl From<Local> for Operand<'_> {
fn from(local: Local) -> Self {
Operand::Place(Place::local(local))
Expand Down
5 changes: 4 additions & 1 deletion libs/@local/hashql/mir/src/builder/body.rs
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Expand Up @@ -311,7 +311,10 @@ macro_rules! body {
(@type $types:ident; Int) => {
$types.integer()
};
(@type $types:ident; ($($sub:tt),*)) => {
(@type $types:ident; ()) => {
$types.tuple([] as [hashql_core::r#type::TypeId; 0])
};
(@type $types:ident; ($($sub:tt),+)) => {
$types.tuple([$($crate::builder::body!(@type $types; $sub)),*])
};
(@type $types:ident; ($($name:ident: $sub:tt),*)) => {
Expand Down
5 changes: 5 additions & 0 deletions libs/@local/hashql/mir/src/builder/rvalue.rs
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Expand Up @@ -224,6 +224,11 @@ macro_rules! rvalue {
rv.closure($def, $env)
}; $payload; $($rest)*)
};
($resume:path; $payload:tt; tuple; $($rest:tt)*) => {
$resume!(@rvalue |rv| {
rv.tuple([] as [!; 0])
}; $payload; $($rest)*)
};
($resume:path; $payload:tt; tuple $($members:tt),+; $($rest:tt)*) => {
$resume!(@rvalue |rv| {
let members = [$($crate::builder::_private::operand!(rv; $members)),*];
Expand Down
7 changes: 3 additions & 4 deletions libs/@local/hashql/mir/src/lib.rs
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Expand Up @@ -14,16 +14,15 @@
// Library Features
allocator_api,
assert_matches,
binary_heap_drain_sorted,
const_type_name,
iter_array_chunks,
iter_collect_into,
iter_intersperse,
maybe_uninit_fill,
step_trait,
string_from_utf8_lossy_owned,
try_trait_v2,
step_trait,
maybe_uninit_fill,
binary_heap_into_iter_sorted,
binary_heap_drain_sorted,
)]
#![expect(clippy::indexing_slicing)]
extern crate alloc;
Expand Down
15 changes: 14 additions & 1 deletion libs/@local/hashql/mir/src/pass/transform/inst_simplify/mod.rs
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Expand Up @@ -107,7 +107,7 @@ use crate::{
location::Location,
operand::Operand,
place::Place,
rvalue::{BinOp, Binary, RValue, Unary},
rvalue::{Aggregate, AggregateKind, BinOp, Binary, RValue, Unary},
statement::Assign,
},
context::MirContext,
Expand Down Expand Up @@ -503,6 +503,19 @@ impl<'heap, A: Allocator> VisitorMut<'heap> for InstSimplifyVisitor<'_, 'heap, A
Ok(())
}

fn visit_rvalue_aggregate(
&mut self,
_: Location,
aggregate: &mut Aggregate<'heap>,
) -> Self::Result<()> {
// Specialize into a unit if it's an empty tuple
if aggregate.kind == AggregateKind::Tuple && aggregate.operands.is_empty() {
self.trampoline = Some(RValue::Load(Operand::Constant(Constant::Unit)));
}

Ok(())
}

fn visit_statement_assign(
&mut self,
location: Location,
Expand Down
73 changes: 50 additions & 23 deletions libs/@local/hashql/mir/src/pass/transform/inst_simplify/tests.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
#![expect(clippy::min_ident_chars, reason = "tests")]
use std::{io::Write as _, path::PathBuf};
use std::{assert_matches::assert_matches, io::Write as _, path::PathBuf};

use bstr::ByteVec as _;
use hashql_core::{
Expand All @@ -12,8 +12,20 @@ use insta::{Settings, assert_snapshot};

use super::InstSimplify;
use crate::{
body::Body, builder::body, context::MirContext, def::DefIdSlice, intern::Interner,
pass::TransformPass as _, pretty::TextFormat,
body::{
Body,
basic_block::BasicBlockId,
constant::Constant,
operand::Operand,
rvalue::RValue,
statement::{Assign, StatementKind},
},
builder::body,
context::MirContext,
def::DefIdSlice,
intern::Interner,
pass::{Changed, TransformPass as _},
pretty::TextFormat,
};

#[track_caller]
Expand Down Expand Up @@ -64,10 +76,6 @@ fn assert_inst_simplify_pass<'heap>(
assert_snapshot!(name, value);
}

// =============================================================================
// Constant Folding (Bitwise on integers, Unary - not in source language)
// =============================================================================

/// Tests constant folding for bitwise AND on integers.
#[test]
fn const_fold_bit_and() {
Expand Down Expand Up @@ -180,10 +188,6 @@ fn const_fold_unary_neg() {
);
}

// =============================================================================
// Bitwise Identity on Integers (x | 0 => x - not in source language)
// =============================================================================

/// Tests identity simplification for bitwise OR with zero.
#[test]
fn identity_bit_or_zero() {
Expand Down Expand Up @@ -212,10 +216,6 @@ fn identity_bit_or_zero() {
);
}

// =============================================================================
// Identical Operand Patterns (BitAnd/BitOr on integers - not in source)
// =============================================================================

/// Tests idempotent simplification for bitwise AND with identical operands.
#[test]
fn identical_operand_bit_and() {
Expand Down Expand Up @@ -272,10 +272,6 @@ fn identical_operand_bit_or() {
);
}

// =============================================================================
// Block Parameter Propagation (requires CFG control)
// =============================================================================

/// Tests constant propagation through block params with single predecessor.
#[test]
fn block_param_single_predecessor() {
Expand Down Expand Up @@ -381,10 +377,6 @@ fn block_param_predecessors_disagree() {
);
}

// =============================================================================
// Idempotent to Constant Forwarding (requires bitwise op)
// =============================================================================

/// Tests that idempotent simplification propagates constants through the result.
#[test]
fn idempotent_to_const_forwarding() {
Expand Down Expand Up @@ -414,3 +406,38 @@ fn idempotent_to_const_forwarding() {
},
);
}

/// Tests that an empty tuple aggregate is simplified to a unit constant.
#[test]
fn empty_tuple_to_unit() {
let heap = Heap::new();
let interner = Interner::new(&heap);
let env = Environment::new(&heap);

let mut body = body!(interner, env; fn@0/0 -> () {
decl result: ();

bb0() {
result = tuple;
return result;
}
});

let changed = InstSimplify::new().run(
&mut MirContext {
heap: &heap,
env: &env,
interner: &interner,
diagnostics: DiagnosticIssues::new(),
},
&mut body,
);
assert_eq!(changed, Changed::Yes);
assert_matches!(
body.basic_blocks[BasicBlockId::START].statements[0].kind,
StatementKind::Assign(Assign {
lhs: _,
rhs: RValue::Load(Operand::Constant(Constant::Unit))
})
);
}
20 changes: 6 additions & 14 deletions libs/@local/hashql/mir/tests/ui/pass/inline/closure-inline.stdout
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