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[StackIR] Drop a set/get pair across a symmetric operation #9162

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Merged
tlively merged 1 commit into from
Sep 29, 2026
Merged

[StackIR] Drop a set/get pair across a symmetric operation #9162

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1 change: 1 addition & 0 deletions src/wasm-stack.h
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Original file line number Diff line number Diff line change
Expand Up @@ -643,6 +643,7 @@ class StackIROptimizer {
void removeAt(Index i);
Index getNumConsumedValues(StackInst* inst);
bool canRemoveSetGetPair(Index setIndex, Index getIndex);
bool isConsumedBySymmetricOp(Index getIndex);
std::unordered_set<LocalGet*> findStringViewDeferredGets();
};

Expand Down
40 changes: 38 additions & 2 deletions src/wasm/wasm-stack-opts.cpp
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Expand Up @@ -21,6 +21,7 @@
#include "ir/branch-utils.h"
#include "ir/iteration.h"
#include "ir/local-graph.h"
#include "ir/properties.h"
#include "pass.h"
#include "wasm-stack.h"
#include "wasm.h"
Expand Down Expand Up @@ -124,6 +125,26 @@ void StackIROptimizer::vacuum() {
}
}

// Whether the local.get at getIndex is consumed by an operation whose operands
// can be swapped.
bool StackIROptimizer::isConsumedBySymmetricOp(Index getIndex) {
Index k = getIndex + 1;
while (k < insts.size() && !insts[k]) {
++k;
}
if (k >= insts.size()) {
return false;
}
auto* inst = insts[k];
if (inst->op != StackInst::Basic) {
return false;
}
if (auto* binary = inst->origin->dynCast<Binary>()) {
return Properties::isSymmetric(binary);
}
return inst->origin->is<RefEq>();
}

@kripken kripken Sep 28, 2026

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This can also check for RefEq

@artemkulyk artemkulyk Sep 28, 2026

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Added RefEq and a test for it.


// If ordered properly, we can avoid a local.set/local.get pair,
// and use the value directly from the stack, for example
// [..produce a value on the stack..]
Expand Down Expand Up @@ -219,11 +240,26 @@ void StackIROptimizer::local2Stack() {
// can reach the set.
if (values.size() > 0) {
Index j = values.size() - 1;
// If an actual value is in the way then the set's value is not on
// top of the stack at the get. That is fine if exactly one value is
// in the way and it is consumed together with the get by an
// operation with interchangeable operands, as then the order does
// not matter.
bool intervening = false;
while (1) {
// If there's an actual value in the way, we've failed.
auto setIndex = values[j];
if (setIndex == null) {
break;
if (intervening || !isConsumedBySymmetricOp(getIndex)) {
// More than one value is in the way, or the value that is in
// the way is not consumed together with the get: give up.
break;
}
intervening = true;
if (j == 0) {
break;
}
j--;
continue;
}
auto* set = insts[setIndex]->origin->cast<LocalSet>();
if (set->index == get->index) {
Expand Down
140 changes: 126 additions & 14 deletions test/lit/passes/optimize-stack-ir.wast
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Expand Up @@ -6,16 +6,18 @@
;; CHECK: (type $FUNCSIG$v (func))
(type $FUNCSIG$v (func))

;; CHECK: (type $5 (func (result i32)))

;; CHECK: (type $6 (func (param i32) (result i32)))

;; CHECK: (type $5 (func (result i32)))

;; CHECK: (type $FUNCSIG$vf (func (param f32)))
(type $FUNCSIG$vf (func (param f32)))
;; CHECK: (type $4 (func (result f64)))

;; CHECK: (type $FUNCSIG$ddd (func (param f64 f64) (result f64)))

;; CHECK: (type $10 (func (param f32) (result f32)))

;; CHECK: (type $FUNCSIG$id (func (param f64) (result i32)))
(type $FUNCSIG$id (func (param f64) (result i32)))
(type $FUNCSIG$ddd (func (param f64 f64) (result f64)))
Expand All @@ -29,6 +31,10 @@
;; CHECK: (type $9 (func (param i32 i64)))
(type $9 (func (param i32 i64)))

;; CHECK: (type $15 (func (param eqref) (result i32)))

;; CHECK: (type $16 (func (param eqref) (result eqref)))

;; CHECK: (import "env" "_emscripten_asm_const_vi" (func $_emscripten_asm_const_vi (type $FUNCSIG$v)))
(import "env" "_emscripten_asm_const_vi" (func $_emscripten_asm_const_vi))

Expand Down Expand Up @@ -1097,24 +1103,44 @@
)
)

;; CHECK: (func $local-to-stack-1c-no (type $6) (param $x i32) (result i32)
;; CHECK: (func $local-to-stack-1c (type $6) (param $x i32) (result i32)
;; CHECK-NEXT: (local $temp i32)
;; CHECK-NEXT: i32.const 1
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: local.set $temp
;; CHECK-NEXT: i32.const 2
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: drop
;; CHECK-NEXT: i32.const 3
;; CHECK-NEXT: local.get $temp
;; CHECK-NEXT: i32.add
;; CHECK-NEXT: )
(func $local-to-stack-1c-no (param $x i32) (result i32)
(func $local-to-stack-1c (param $x i32) (result i32)
(local $temp i32)
(local.set $temp (call $local-to-stack (i32.const 1)))
(drop (call $local-to-stack (i32.const 2)))
(i32.add
(i32.const 3) ;; this is in the way
(i32.const 3) ;; in the way, but the add is commutative so we can
(local.get $temp) ;; still use the value on the stack
)
)

;; CHECK: (func $local-to-stack-1d-sub-no (type $6) (param $x i32) (result i32)
;; CHECK-NEXT: (local $temp i32)
;; CHECK-NEXT: i32.const 1
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: local.set $temp
;; CHECK-NEXT: i32.const 2
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: drop
;; CHECK-NEXT: i32.const 3
;; CHECK-NEXT: local.get $temp
;; CHECK-NEXT: i32.sub
;; CHECK-NEXT: )
(func $local-to-stack-1d-sub-no (param $x i32) (result i32)
(local $temp i32)
(local.set $temp (call $local-to-stack (i32.const 1)))
(drop (call $local-to-stack (i32.const 2)))
(i32.sub
(i32.const 3) ;; not commutative: the set/get pair must stay
(local.get $temp)
)
)
Expand Down Expand Up @@ -1292,29 +1318,27 @@
(local.get $temp2)
)

;; CHECK: (func $local-to-stack-overlapping-multi-8-no (type $6) (param $x i32) (result i32)
;; CHECK: (func $local-to-stack-overlapping-multi-8 (type $6) (param $x i32) (result i32)
;; CHECK-NEXT: (local $temp1 i32)
;; CHECK-NEXT: (local $temp2 i32)
;; CHECK-NEXT: i32.const 1
;; CHECK-NEXT: call $local-to-stack-multi-4
;; CHECK-NEXT: local.set $temp1
;; CHECK-NEXT: i32.const 1
;; CHECK-NEXT: call $local-to-stack-multi-4
;; CHECK-NEXT: i32.const 3
;; CHECK-NEXT: call $local-to-stack-multi-4
;; CHECK-NEXT: drop
;; CHECK-NEXT: local.get $temp1
;; CHECK-NEXT: i32.add
;; CHECK-NEXT: )
(func $local-to-stack-overlapping-multi-8-no (param $x i32) (result i32)
(func $local-to-stack-overlapping-multi-8 (param $x i32) (result i32)
(local $temp1 i32)
(local $temp2 i32)
(local.set $temp1 (call $local-to-stack-multi-4 (i32.const 1)))
(local.set $temp2 (call $local-to-stack-multi-4 (i32.const 1)))
(drop (call $local-to-stack-multi-4 (i32.const 3)))
(i32.add
(local.get $temp2) ;; the timing
(local.get $temp1) ;; it sucks
(i32.add ;; the operands are flipped, but the add is commutative
(local.get $temp2)
(local.get $temp1)
)
)

Expand Down Expand Up @@ -1459,4 +1483,92 @@
)
)
)

;; A ref.eq with an intervening value: its operands can be swapped.
;; CHECK: (func $local-to-stack-ref-eq (type $15) (param $x eqref) (result i32)
;; CHECK-NEXT: (local $temp eqref)
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $eqref-value
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $eqref-value
;; CHECK-NEXT: drop
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: ref.eq
;; CHECK-NEXT: )
(func $local-to-stack-ref-eq (param $x eqref) (result i32)
(local $temp eqref)
(local.set $temp (call $eqref-value (local.get $x)))
(drop (call $eqref-value (local.get $x)))
(ref.eq
(local.get $x)
(local.get $temp)
)
)

;; CHECK: (func $eqref-value (type $16) (param $x eqref) (result eqref)
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $eqref-value
;; CHECK-NEXT: )
(func $eqref-value (param $x eqref) (result eqref)
(call $eqref-value (local.get $x))
)

;; f32.min has swappable operands, so the set/get pair can be removed.
;; CHECK: (func $local-to-stack-f32-min (type $10) (param $x f32) (result f32)
;; CHECK-NEXT: (local $temp f32)
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $float-value
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $float-value
;; CHECK-NEXT: drop
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: f32.min
;; CHECK-NEXT: )
(func $local-to-stack-f32-min (param $x f32) (result f32)
(local $temp f32)
(local.set $temp (call $float-value (local.get $x)))
(drop (call $float-value (local.get $x)))
(f32.min
(local.get $x)
(local.get $temp)
)
)

;; CHECK: (func $float-value (type $10) (param $x f32) (result f32)
;; CHECK-NEXT: local.get $x
;; CHECK-NEXT: call $float-value
;; CHECK-NEXT: )
(func $float-value (param $x f32) (result f32)
(call $float-value (local.get $x))
)

;; Two values are in the way, so the set/get pair must stay.
;; CHECK: (func $local-to-stack-two-in-the-way (type $6) (param $x i32) (result i32)
;; CHECK-NEXT: (local $temp i32)
;; CHECK-NEXT: i32.const 1
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: local.set $temp
;; CHECK-NEXT: i32.const 2
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: drop
;; CHECK-NEXT: i32.const 3
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: i32.const 4
;; CHECK-NEXT: call $local-to-stack
;; CHECK-NEXT: local.get $temp
;; CHECK-NEXT: i32.add
;; CHECK-NEXT: i32.add
;; CHECK-NEXT: )
(func $local-to-stack-two-in-the-way (param $x i32) (result i32)
(local $temp i32)
(local.set $temp (call $local-to-stack (i32.const 1)))
(drop (call $local-to-stack (i32.const 2)))
(i32.add
(call $local-to-stack (i32.const 3))
(i32.add
(call $local-to-stack (i32.const 4))
(local.get $temp)
)
)
)
)
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