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ConstraintAnalysis fuzz bug: Do not AND after a branch is not taken #9035

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ConstraintAnalysis fuzz bug: Do not AND after a branch is not taken #9035

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8 changes: 6 additions & 2 deletions src/passes/ConstraintAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -655,13 +655,17 @@ struct ConstraintAnalysis
if (branch.constraint.op == Abstract::LtS ||
branch.constraint.op == Abstract::LeS) {
constraints.set(branch.local, branch.constraint);
constraints.approximateAnd(branch.local, {GeS, {*N}});
if (!constraints.unreachable) {
constraints.approximateAnd(branch.local, {GeS, {*N}});
}
return true;
}
if (branch.constraint.op == Abstract::LtU ||
branch.constraint.op == Abstract::LeU) {
constraints.set(branch.local, branch.constraint);
constraints.approximateAnd(branch.local, {GeU, {*N}});
if (!constraints.unreachable) {
constraints.approximateAnd(branch.local, {GeU, {*N}});
}
return true;
}

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53 changes: 53 additions & 0 deletions test/lit/passes/constraint-analysis-loops.wast
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Expand Up @@ -1520,4 +1520,57 @@
)
)
)

;; CHECK: (func $impossible-branch (type $0)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (local $y i32)
;; CHECK-NEXT: (loop $loop
;; CHECK-NEXT: (br_if $loop
;; CHECK-NEXT: (i32.lt_s
;; CHECK-NEXT: (local.get $x)
;; CHECK-NEXT: (local.get $y)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $impossible-branch
(local $x i32)
(local $y i32)
(loop $loop
;; x == y == 0, so x < y leads to a contradiction, and we never branch
;; back up to the loop. We should not error here.
(br_if $loop
(i32.lt_s
(local.get $x)
(local.get $y)
)
)
)
)

;; CHECK: (func $impossible-branch-unsigned (type $0)
;; CHECK-NEXT: (local $x i32)
;; CHECK-NEXT: (local $y i32)
;; CHECK-NEXT: (loop $loop
;; CHECK-NEXT: (br_if $loop
;; CHECK-NEXT: (i32.lt_u
;; CHECK-NEXT: (local.get $x)
;; CHECK-NEXT: (local.get $y)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $impossible-branch-unsigned
(local $x i32)
(local $y i32)
;; As above, but unsigned.
(loop $loop
(br_if $loop
(i32.lt_u
(local.get $x)
(local.get $y)
)
)
)
)
)
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