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Optimize instructions tee get relational 7672 #9148

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68f8693
[optimize-instructions] Fold relational comparisons of tee/get pairs
ArkadySkv Sep 23, 2026
e9bad33
Add a guard against a future change that duplicates the comparison in…
ArkadySkv Sep 23, 2026
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41 changes: 41 additions & 0 deletions src/passes/OptimizeInstructions.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4990,6 +4990,47 @@ struct OptimizeInstructions
using namespace Match;

auto type = curr->right->type;

// (rel (local.tee $n X) (local.get $n)) compares X against itself, so
// the result is a constant. Evaluate X once for its side effects,
// discard the tee's value, and return the constant. Do not duplicate X:
// it may trap or write (the reproduction is a chain of loads).
if (areMatchingTeeAndGet(curr->left, curr->right)) {
bool isTrue;
switch (curr->op) {
case GtSInt32:
case GtUInt32:
case LtSInt32:
case LtUInt32:
case GtSInt64:
case GtUInt64:
case LtSInt64:
case LtUInt64:
case NeInt32:
case NeInt64:
isTrue = false;
break;
case GeSInt32:
case GeUInt32:
case LeSInt32:
case LeUInt32:
case GeSInt64:
case GeUInt64:
case LeSInt64:
case LeUInt64:
case EqInt32:
case EqInt64:
isTrue = true;
break;
default:
WASM_UNREACHABLE("unexpected relational op");
}
Builder builder(*getModule());
return builder.makeSequence(
builder.makeDrop(curr->left),
builder.makeConst(Literal::makeFromInt32(isTrue, Type::i32)));
}

if (curr->left->type.isInteger()) {
if (curr->op == Abstract::getBinary(type, Abstract::Eq) ||
curr->op == Abstract::getBinary(type, Abstract::Ne)) {
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22 changes: 22 additions & 0 deletions test/lit/passes/optimize-instructions-tee-get-comparison.wast
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@@ -0,0 +1,22 @@
;; RUN: wasm-opt -all --optimize-instructions %s -S -o - | filecheck %s

;; (i32.gt_s (local.tee $0 X) (local.get $0)) is X compared with itself,
;; always 0. The tee and its load are preserved for trap behavior; the
;; comparison folds to a constant.
;; CHECK: (drop
;; CHECK-NEXT: (local.tee $0
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 0)
;; NOT: i32.gt_s
(module
(memory 1)
(func $f (result i32) (local $0 i32)
(i32.gt_s
(local.tee $0 (i32.load (i32.const 0)))
(local.get $0))
)
)
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