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Merged
merged 25 commits into from
May 2, 2025
Merged

Optimize block tails where a dropped br_if's value is redundant #7506

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2312382
opt for #7489
xuruiyang2002 Apr 16, 2025
4c8983f
tests
xuruiyang2002 Apr 16, 2025
408b606
tests
xuruiyang2002 Apr 16, 2025
dd66eac
Fix: ensure value exists
xuruiyang2002 Apr 17, 2025
18ae939
Update src/passes/RemoveUnusedBrs.cpp
xuruiyang2002 Apr 22, 2025
4ce7032
Rename brk to br
xuruiyang2002 Apr 22, 2025
541906d
Use hasUnremovableSideEffects instead of hasSideEffects
xuruiyang2002 Apr 22, 2025
71bcb13
If-check step by step to avoid wasted work
xuruiyang2002 Apr 22, 2025
18dbc09
Optimization performed only when br_if targets its parent
xuruiyang2002 Apr 22, 2025
8a1f49b
Add a test
xuruiyang2002 Apr 22, 2025
c634b9f
Update src/passes/RemoveUnusedBrs.cpp
xuruiyang2002 Apr 25, 2025
659ffa3
Update src/passes/RemoveUnusedBrs.cpp
xuruiyang2002 Apr 25, 2025
8ec64c9
Update src/passes/RemoveUnusedBrs.cpp
xuruiyang2002 Apr 25, 2025
f9b3b84
Update src/passes/RemoveUnusedBrs.cpp
xuruiyang2002 Apr 25, 2025
e64af88
Update test/lit/passes/remove-unused-brs.wast
xuruiyang2002 Apr 25, 2025
d5de05c
Update test/lit/passes/remove-unused-brs.wast
xuruiyang2002 Apr 25, 2025
af88eb0
Update test cases
xuruiyang2002 Apr 25, 2025
30d4af7
Fix typo
xuruiyang2002 Apr 30, 2025
66151b5
Update test/lit/passes/remove-unused-brs.wast
xuruiyang2002 Apr 30, 2025
c60d693
Update test
xuruiyang2002 Apr 30, 2025
c2fa4a7
Fix: br->condition is null
xuruiyang2002 Apr 30, 2025
66ac882
Update
xuruiyang2002 May 1, 2025
b47ae4f
Add a test
xuruiyang2002 May 1, 2025
d6b6f36
Update test/lit/passes/remove-unused-brs.wast
kripken May 2, 2025
1d4ec95
Update test/lit/passes/remove-unused-brs.wast
kripken May 2, 2025
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39 changes: 39 additions & 0 deletions src/passes/RemoveUnusedBrs.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1258,6 +1258,45 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
tablify(curr);
// Pattern-patch ifs, recreating them when it makes sense.
restructureIf(curr);

// Optimize block tails where a dropped `br_if`'s value is redundant
// when the br_if targets the block itself:
//
// (block $block (result i32)
// ..
// (drop
// (br_if $block ;; <- MUST target parent $block
// (value)
// (condition)
// )
// )
// (value) ;; <- MUST be same as br_if's value
// )
// =>
// (block $block (result i32)
// ..
// (drop
// (condition)
// )
// (value)
// )
size_t size = curr->list.size();
auto* secondLast = curr->list[size - 2];
auto* last = curr->list[size - 1];
if (auto* drop = secondLast->dynCast<Drop>()) {
if (auto* br = drop->value->dynCast<Break>();
br && br->value && br->condition) {
if (br->name == curr->name) {
if (!EffectAnalyzer(passOptions, *getModule(), br->value)
.hasUnremovableSideEffects()) {
if (ExpressionAnalyzer::equal(br->value, last)) {
// All conditions met, perform the update.
drop->value = br->condition;
}
}
}
}
}
}
}

Expand Down
166 changes: 146 additions & 20 deletions test/lit/passes/remove-unused-brs.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@

(module
;; Regression test in which we need to calculate a proper LUB.
;; CHECK: (func $selectify-fresh-lub (type $3) (param $x i32) (result anyref)
;; CHECK: (func $selectify-fresh-lub (type $4) (param $x i32) (result anyref)
;; CHECK-NEXT: (select (result i31ref)
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: (ref.i31
Expand All @@ -30,7 +30,7 @@
)
)

;; CHECK: (func $selectify-simple (type $1) (param $0 i32) (result i32)
;; CHECK: (func $selectify-simple (type $0) (param $0 i32) (result i32)
;; CHECK-NEXT: (select
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: (i32.lt_u
Expand Down Expand Up @@ -73,7 +73,7 @@
)
)

;; CHECK: (func $restructure-br_if (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (local.get $x)
;; CHECK-NEXT: (then
Expand Down Expand Up @@ -104,12 +104,12 @@
)
)

;; CHECK: (func $nothing (type $0)
;; CHECK: (func $nothing (type $1)
;; CHECK-NEXT: )
(func $nothing)


;; CHECK: (func $restructure-br_if-condition-reorderable (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-condition-reorderable (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (block (result i32)
;; CHECK-NEXT: (call $nothing)
Expand Down Expand Up @@ -146,7 +146,7 @@
)
)

;; CHECK: (func $restructure-br_if-value-effectful (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-value-effectful (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (select
;; CHECK-NEXT: (block (result i32)
;; CHECK-NEXT: (call $nothing)
Expand Down Expand Up @@ -188,7 +188,7 @@
)
)

;; CHECK: (func $restructure-br_if-value-effectful-corner-case-1 (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-value-effectful-corner-case-1 (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (block $x (result i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $x
Expand Down Expand Up @@ -226,14 +226,14 @@
)
)

;; CHECK: (func $get-i32 (type $4) (result i32)
;; CHECK: (func $get-i32 (type $2) (result i32)
;; CHECK-NEXT: (i32.const 400)
;; CHECK-NEXT: )
(func $get-i32 (result i32)
(i32.const 400)
)

;; CHECK: (func $restructure-br_if-value-effectful-corner-case-2 (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-value-effectful-corner-case-2 (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (block $x (result i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $x
Expand Down Expand Up @@ -272,7 +272,7 @@
(call $get-i32)
)
)
;; CHECK: (func $restructure-br_if-value-effectful-corner-case-3 (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-value-effectful-corner-case-3 (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (block $x (result i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $x
Expand Down Expand Up @@ -305,7 +305,7 @@
)
)

;; CHECK: (func $restructure-br_if-value-effectful-corner-case-4 (type $1) (param $x i32) (result i32)
;; CHECK: (func $restructure-br_if-value-effectful-corner-case-4 (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (block $x (result i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $x
Expand Down Expand Up @@ -340,9 +340,135 @@
)
)

;; CHECK: (func $restructure-select-no-multivalue (type $0)
;; CHECK: (func $restructure-br_if-value-redundant-in-block-tail-1 (type $2) (result i32)
;; CHECK-NEXT: (block $parent (result i32)
;; CHECK-NEXT: (call $nothing)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $restructure-br_if-value-redundant-in-block-tail-1 (result i32)
;; The br_if's value is equal to the value right after it, so we can remove it.
(block $parent (result i32)
(call $nothing)
(drop
(br_if $parent
(i32.const 1)
(call $get-i32)
)
)
(i32.const 1)
)
)

;; CHECK: (func $restructure-br_if-value-redundant-in-block-tail-2 (type $2) (result i32)
;; CHECK-NEXT: (block $parent (result i32)
;; CHECK-NEXT: (call $nothing)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $parent
;; CHECK-NEXT: (i32.const 2)
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $restructure-br_if-value-redundant-in-block-tail-2 (result i32)
;; As above, but now the value is different, so we do not optimize
(block $parent (result i32)
(call $nothing)
(drop
(br_if $parent
(i32.const 2)
(call $get-i32)
)
)
(i32.const 1)
)
)

;; CHECK: (func $restructure-br_if-value-redundant-in-block-tail-3 (type $0) (param $x i32) (result i32)
;; CHECK-NEXT: (block $parent (result i32)
;; CHECK-NEXT: (call $nothing)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $parent
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $restructure-br_if-value-redundant-in-block-tail-3 (param $x i32) (result i32)
;; As above, but now the value has effects, so we do not optimize
(block $parent (result i32)
(call $nothing)
(drop
(br_if $parent
(call $get-i32)
(call $get-i32)
)
)
(call $get-i32)
)
)

;; CHECK: (func $restructure-br_if-value-redundant-in-block-tail-4 (type $2) (result i32)
;; CHECK-NEXT: (block $outer (result i32)
;; CHECK-NEXT: (block $inner (result i32)
;; CHECK-NEXT: (call $nothing)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (br_if $outer
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: (call $get-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $restructure-br_if-value-redundant-in-block-tail-4 (result i32)
;; As above, but the br_if targets another block, so we do not optimize.
(block $outer (result i32)
(block $inner (result i32)
(call $nothing)
(drop
(br_if $outer
(i32.const 1)
(call $get-i32)
)
)
(i32.const 1)
)
)
)

;; CHECK: (func $restructure-br_if-value-redundant-in-block-tail-5 (type $2) (result i32)
;; CHECK-NEXT: (block $parent (result i32)
;; CHECK-NEXT: (call $nothing)
;; CHECK-NEXT: (br $parent
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $restructure-br_if-value-redundant-in-block-tail-5 (result i32)
;; As above, but the br lacks a condition. We do not bother to optimize
;; the dead code after it, but also should not error here.
(block $parent (result i32)
(call $nothing)
(br $parent
(i32.const 1)
)
(i32.const 1)
)
)

;; CHECK: (func $restructure-select-no-multivalue (type $1)
;; CHECK-NEXT: (tuple.drop 2
;; CHECK-NEXT: (block $block (type $2) (result i32 i32)
;; CHECK-NEXT: (block $block (type $3) (result i32 i32)
;; CHECK-NEXT: (tuple.drop 2
;; CHECK-NEXT: (br_if $block
;; CHECK-NEXT: (tuple.make 2
Expand Down Expand Up @@ -387,7 +513,7 @@
)
)

;; CHECK: (func $if-of-if (type $0)
;; CHECK: (func $if-of-if (type $1)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (if
;; CHECK-NEXT: (select
Expand Down Expand Up @@ -421,7 +547,7 @@
)
)

;; CHECK: (func $if-of-if-but-side-effects (type $0)
;; CHECK: (func $if-of-if-but-side-effects (type $1)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (if
;; CHECK-NEXT: (local.tee $x
Expand Down Expand Up @@ -460,7 +586,7 @@
)
)

;; CHECK: (func $if-of-if-but-too-costly (type $0)
;; CHECK: (func $if-of-if-but-too-costly (type $1)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (if
;; CHECK-NEXT: (local.tee $x
Expand Down Expand Up @@ -515,7 +641,7 @@
)
)

;; CHECK: (func $if-of-if-but-inner-else (type $0)
;; CHECK: (func $if-of-if-but-inner-else (type $1)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (if
;; CHECK-NEXT: (local.tee $x
Expand Down Expand Up @@ -555,7 +681,7 @@
)
)

;; CHECK: (func $if-of-if-but-outer-else (type $0)
;; CHECK: (func $if-of-if-but-outer-else (type $1)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (if
;; CHECK-NEXT: (local.tee $x
Expand Down Expand Up @@ -595,7 +721,7 @@
)
)

;; CHECK: (func $unreachable-if (type $0)
;; CHECK: (func $unreachable-if (type $1)
;; CHECK-NEXT: (block $block
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (unreachable)
Expand Down Expand Up @@ -625,7 +751,7 @@
)
)

;; CHECK: (func $loop-with-unreachable-if (type $0)
;; CHECK: (func $loop-with-unreachable-if (type $1)
;; CHECK-NEXT: (loop $label
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (unreachable)
Expand Down
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