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WIP: Trying to promote const local array using GVN pass #5

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ff0c6b7
add regression test
tesuji Jun 10, 2024
46a0ead
wip
tesuji Jun 11, 2024
49b77d1
wip
tesuji Jun 11, 2024
2ab8340
set memplace as immutable
tesuji Jun 12, 2024
d67fe2d
interpret: use trace to reduce noice
tesuji Jun 13, 2024
9d58e3f
remove redundant condition
tesuji Jun 13, 2024
2505da6
clearer reasoning
tesuji Jun 13, 2024
c4d3149
ignore nested arrays
tesuji Jun 13, 2024
54741c0
cache propagated const
tesuji Jun 13, 2024
5ae4fcb
bless
tesuji Jun 13, 2024
5f8d330
add codegen test
tesuji Jun 13, 2024
95c131f
fmt
tesuji Jun 13, 2024
6c0fe34
bless else
tesuji Jun 13, 2024
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29 changes: 27 additions & 2 deletions compiler/rustc_mir_transform/src/gvn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,7 +367,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
#[instrument(level = "trace", skip(self), ret)]
fn eval_to_const(&mut self, value: VnIndex) -> Option<OpTy<'tcx>> {
use Value::*;
let op = match *self.get(value) {
let vvalue = self.get(value);
debug!(?vvalue);
let op = match *vvalue {
Opaque(_) => return None,
// Do not bother evaluating repeat expressions. This would uselessly consume memory.
Repeat(..) => return None,
Expand All @@ -376,10 +378,11 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
self.ecx.eval_mir_constant(value, DUMMY_SP, None).ok()?
}
Aggregate(kind, variant, ref fields) => {
debug!(?kind, ?variant, ?fields);
let fields = fields
.iter()
.map(|&f| self.evaluated[f].as_ref())
.collect::<Option<Vec<_>>>()?;
.collect::<Option<Vec<&OpTy<'_>>>>()?;
let ty = match kind {
AggregateTy::Array => {
assert!(fields.len() > 0);
Expand Down Expand Up @@ -407,6 +410,26 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
};
let ptr_imm = Immediate::new_pointer_with_meta(data, meta, &self.ecx);
ImmTy::from_immediate(ptr_imm, ty).into()
} else if matches!(kind, AggregateTy::Array) {
let mut mplace = None;
let alloc_id = self.ecx.intern_with_temp_alloc(ty, |ecx, dest| {
for (field_index, op) in fields.iter().copied().enumerate() {
let field_dest = ecx.project_field(dest, field_index)?;
ecx.copy_op(op, &field_dest)?;
}

let dest = dest.assert_mem_place();
//ecx.alloc_mark_immutable(dest.ptr().provenance.unwrap().alloc_id()).unwrap();
let dest = dest.map_provenance(|prov| prov.as_immutable());
mplace.replace(dest);
Ok(())
}).ok()?;
let GlobalAlloc::Memory(_alloc) = self.tcx.global_alloc(alloc_id) else {
bug!()
};
let mplace = mplace.unwrap();
debug!(?mplace);
return Some(mplace.into());
} else if matches!(ty.abi, Abi::Scalar(..) | Abi::ScalarPair(..)) {
let dest = self.ecx.allocate(ty, MemoryKind::Stack).ok()?;
let variant_dest = if let Some(variant) = variant {
Expand All @@ -429,6 +452,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
}

Projection(base, elem) => {
debug!(?base, ?elem);
let value = self.evaluated[base].as_ref()?;
let elem = match elem {
ProjectionElem::Deref => ProjectionElem::Deref,
Expand All @@ -450,6 +474,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
self.ecx.project(value, elem).ok()?
}
Address { place, kind, provenance: _ } => {
debug!(?place, ?kind);
if !place.is_indirect_first_projection() {
return None;
}
Expand Down
44 changes: 44 additions & 0 deletions tests/mir-opt/const_array_locals.main.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,44 @@
- // MIR for `main` before GVN
+ // MIR for `main` after GVN

fn main() -> () {
let mut _0: ();
let _1: [i32; 32];
let mut _4: &[i32; 32];
let _5: [i32; 32];
scope 1 {
debug _arr => _1;
let _2: [i32; 32];
scope 2 {
debug _barr => _2;
let _3: [i32; 32];
let mut _6: &[i32; 32];
scope 3 {
debug _darr => _3;
}
}
}

bb0: {
- StorageLive(_1);
+ nop;
_1 = [const 255_i32, const 105_i32, const 15_i32, const 39_i32, const 62_i32, const 251_i32, const 191_i32, const 178_i32, const 9_i32, const 4_i32, const 56_i32, const 221_i32, const 193_i32, const 164_i32, const 194_i32, const 197_i32, const 6_i32, const 243_i32, const 218_i32, const 171_i32, const 87_i32, const 247_i32, const 104_i32, const 159_i32, const 22_i32, const 157_i32, const 105_i32, const 31_i32, const 96_i32, const 173_i32, const 50_i32, const 1_i32];
StorageLive(_2);
- _2 = [const 255_i32, const 105_i32, const 15_i32, const 39_i32, const 62_i32, const 251_i32, const 191_i32, const 178_i32, const 9_i32, const 4_i32, const 56_i32, const 221_i32, const 193_i32, const 164_i32, const 194_i32, const 197_i32, const 6_i32, const 243_i32, const 218_i32, const 171_i32, const 87_i32, const 247_i32, const 104_i32, const 159_i32, const 22_i32, const 157_i32, const 105_i32, const 31_i32, const 96_i32, const 173_i32, const 50_i32, const 1_i32];
+ _2 = _1;
StorageLive(_3);
StorageLive(_4);
_6 = const main::promoted[0];
_4 = &(*_6);
- _3 = (*_4);
+ _3 = (*_6);
StorageDead(_4);
_0 = const ();
StorageDead(_3);
StorageDead(_2);
- StorageDead(_1);
+ nop;
return;
}
}

46 changes: 46 additions & 0 deletions tests/mir-opt/const_array_locals.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,46 @@
//@ test-mir-pass: GVN
#![feature(repr_simd)]

// #[repr(simd)]
// struct F32x8([f32; 8]);

// EMIT_MIR const_array_locals.main.GVN.diff
// CHECK-LABEL: fn main(
#[rustfmt::skip]
pub fn main() {
// CHECK: let [[array_lit:_.*]]: [i32; 32];
// CHECK: debug _arr => [[arr:_.*]];

let _arr = [
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@tesuji tesuji Jun 12, 2024 •
edited
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With commits[3], this now returns as a immutable memplace: Some(OpTy { op: Indirect(MemPlace { ptr: alloc3<imm>, meta: None, misaligned: None }), ty: [i32; 32] }).

But in the mir diff, _arr still is not promoted.

255, 105, 15, 39, 62, 251, 191, 178, 9, 4, 56, 221,
193, 164, 194, 197, 6, 243, 218, 171, 87, 247, 104,
159, 22, 157, 105, 31, 96, 173, 50, 1,
];
let _barr = [
255, 105, 15, 39, 62, 251, 191, 178, 9, 4, 56, 221,
193, 164, 194, 197, 6, 243, 218, 171, 87, 247, 104,
159, 22, 157, 105, 31, 96, 173, 50, 1,
];
// let _foo = [
// [255, 105, 15, 39, 62, 251, 191, 178, 9, 4, 56, 221],
// [193, 164, 194, 197, 6, 243, 218, 171, 87, 247, 104, 42],
// ];
let _darr = *&[
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This returns Some(OpTy { op: Indirect(MemPlace { ptr: alloc2<imm>, meta: None, misaligned: None }), ty: [i32; 32] })

255, 105, 15, 39, 62, 251, 191, 178, 9, 4, 56, 221,
193, 164, 194, 197, 6, 243, 218, 171, 87, 247, 104,
159, 22, 157, 105, 31, 96, 173, 50, 1,
];

// consume([255, 105, 15, 39, 62, 251, 191, 178, 9, 4, 56, 221,
// 193, 164, 194, 197, 6, 243, 218, 171, 87, 247, 104,
// 159, 22, 157, 105, 31, 96, 173, 50, 1,]);

// let _f = F32x8([1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0]);

// // ice
// [[1, 0, 0], [0, 1, 0], [0, 0, 1]]; // 2D array
}

// fn consume(_arr: [u16; 32]) {
// unimplemented!()
// }