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Push struct.new down to make it more likely that heap stores can be optimized. #6584

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merged 7 commits into from
May 28, 2024
Merged

Push struct.new down to make it more likely that heap stores can be optimized. #6584

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95300e6
Push struct.new down to make it more likely to optimize struct.sets.
rluble May 12, 2024
1b8e5f2
More fixes.
rluble May 12, 2024
1ae61a5
Fix .wast.
rluble May 12, 2024
9487c70
Clean up some of the logic.
rluble May 14, 2024
02409d2
More fixes.
rluble May 14, 2024
c751f8b
Fixes
rluble May 21, 2024
89129a6
More fixes.
rluble May 24, 2024
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72 changes: 55 additions & 17 deletions src/passes/OptimizeInstructions.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1864,11 +1864,9 @@ struct OptimizeInstructions
// =>
// (local.set $x (struct.new X' Y Z))
//
// We also handle other struct.sets immediately after this one, but we only
// handle the case where they are all in sequence and right after the
// local.set (anything in the middle of this pattern will stop us from
// optimizing later struct.sets, which might be improved later but would
// require an analysis of effects TODO).
// We also handle other struct.sets immediately after this one. If the
// instruction following the new is not a struct.set we push the new down if
// possible.
void optimizeHeapStores(ExpressionList& list) {
for (Index i = 0; i < list.size(); i++) {
auto* localSet = list[i]->dynCast<LocalSet>();
Expand All @@ -1880,30 +1878,70 @@ struct OptimizeInstructions
continue;
}

// This local.set of a struct.new looks good. Find struct.sets after it
// to optimize.
for (Index j = i + 1; j < list.size(); j++) {
// This local.set of a struct.new looks good. Find struct.sets after it to
// optimize.
Index localSetIndex = i;
for (Index j = localSetIndex + 1; j < list.size(); j++) {

// Check that the next instruction is a struct.set on the same local as
// the struct.new.
auto* structSet = list[j]->dynCast<StructSet>();
if (!structSet) {
// Any time the pattern no longer matches, stop optimizing possible
// struct.sets for this struct.new.
break;
}
auto* localGet = structSet->ref->dynCast<LocalGet>();
if (!localGet || localGet->index != localSet->index) {
auto* localGet =
structSet ? structSet->ref->dynCast<LocalGet>() : nullptr;
if (!structSet || !localGet || localGet->index != localSet->index) {
// Any time the pattern no longer matches, we try to push the
// struct.new further down but if it is not possible we stop
// optimizing possible struct.sets for this struct.new.
if (trySwap(list, localSetIndex, j)) {
// Update the index and continue to try again.
localSetIndex = j;
continue;
}
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break;
}

// The pattern matches, try to optimize.
if (!optimizeSubsequentStructSet(new_, structSet, localGet->index)) {
break;
} else {
// Success. Replace the set with a nop, and continue to
// perhaps optimize more.
// Success. Replace the set with a nop, and continue to perhaps
// optimize more.
ExpressionManipulator::nop(structSet);
}
}
}
}

// Helper function for optimizeHeapStores. Tries pushing the struct.new at
// index i down to index j, swapping it with the instruction already at j, so
// that it is closer to (potential) later struct.sets.
bool trySwap(ExpressionList& list, Index i, Index j) {
if (j == list.size() - 1) {
// There is no reason to swap with the last element of the list as it
// won't match the pattern because there wont be anything after. This also
// avoids swapping an instruction that does not leave anything in the
// stack by one that could leave something, and that which would be
// incorrect.
return false;
}

if (list[j]->is<LocalSet>() &&
list[j]->dynCast<LocalSet>()->value->is<StructNew>()) {
// Don't swap two struct.new instructions to avoid going back and forth.
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return false;
}
// Check if the two expressions can be swapped safely considering their
// effects.
auto firstEffects = effects(list[i]);
auto secondEffects = effects(list[j]);
if (secondEffects.invalidates(firstEffects)) {
return false;
}
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std::swap(list[i], list[j]);
return true;
}

// Given a struct.new and a struct.set that occurs right after it, and that
// applies to the same data, try to apply the set during the new. This can be
// either with a nested tee:
Expand Down
66 changes: 54 additions & 12 deletions test/lit/passes/optimize-instructions-gc-heap.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -9,11 +9,10 @@
;; CHECK: (type $struct (struct (field (mut i32))))
(type $struct (struct (field (mut i32))))

;; CHECK: (type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))

;; CHECK: (type $struct2 (struct (field (mut i32)) (field (mut i32))))
(type $struct2 (struct (field (mut i32)) (field (mut i32))))

;; CHECK: (type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))
(type $struct3 (struct (field (mut i32)) (field (mut i32)) (field (mut i32))))

;; CHECK: (func $tee (type $1)
Expand Down Expand Up @@ -272,26 +271,72 @@

;; CHECK: (func $pattern-breaker (type $1)
;; CHECK-NEXT: (local $ref (ref null $struct))
;; CHECK-NEXT: (local $ref2 (ref null $struct))
;; CHECK-NEXT: (local.set $ref
;; CHECK-NEXT: (struct.new $struct
;; CHECK-NEXT: (i32.const 10)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (local.set $ref2
;; CHECK-NEXT: (local.get $ref)
;; CHECK-NEXT: )
;; CHECK-NEXT: (struct.set $struct 0
;; CHECK-NEXT: (local.get $ref)
;; CHECK-NEXT: (i32.const 20)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $pattern-breaker
(local $ref (ref null $struct))
(local $ref2 (ref null $struct))
(local.set $ref
(struct.new $struct
(i32.const 10)
)
)
;; Any instruction that can not be swapped and is not
;; the expected struct.set breaks the pattern.
(local.set $ref2 (local.get $ref))
(struct.set $struct 0
(local.get $ref)
(i32.const 20)
)
)

;; CHECK: (func $dont-swap-subsequent-struct-new (type $1)
;; CHECK-NEXT: (local $ref (ref null $struct))
;; CHECK-NEXT: (local $ref2 (ref null $struct))
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (local.set $ref
;; CHECK-NEXT: (struct.new $struct
;; CHECK-NEXT: (i32.const 10)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $ref2
;; CHECK-NEXT: (struct.new $struct
;; CHECK-NEXT: (i32.const 20)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (struct.set $struct 0
;; CHECK-NEXT: (local.get $ref)
;; CHECK-NEXT: (i32.const 20)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $dont-swap-subsequent-struct-new
(local $ref (ref null $struct))
(local $ref2 (ref null $struct))
(local.set $ref
(struct.new $struct
(i32.const 10)
)
)
;; Anything that we don't recognize breaks the pattern.
(nop)
;; We do not swap with another local.set of struct.new.
(local.set $ref2
(struct.new $struct
(i32.const 20)
)
)
;; last instruction in the block won't be swapped.
(struct.set $struct 0
(local.get $ref)
(i32.const 20)
Expand Down Expand Up @@ -611,20 +656,17 @@
;; CHECK: (func $many-news (type $1)
;; CHECK-NEXT: (local $ref (ref null $struct3))
;; CHECK-NEXT: (local $ref2 (ref null $struct3))
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (local.set $ref
;; CHECK-NEXT: (struct.new $struct3
;; CHECK-NEXT: (i32.const 40)
;; CHECK-NEXT: (i32.const 50)
;; CHECK-NEXT: (i32.const 30)
;; CHECK-NEXT: (i32.const 60)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (struct.set $struct3 2
;; CHECK-NEXT: (local.get $ref)
;; CHECK-NEXT: (i32.const 60)
;; CHECK-NEXT: )
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (local.set $ref
;; CHECK-NEXT: (struct.new $struct3
;; CHECK-NEXT: (i32.const 400)
Expand Down