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Fix Vacuuming of code leading up to an infinite loop (WebAssembly#6632)
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We had that logic right in other places, but the specific part of Vacuum that
looks at code that leads up to an unreachable did not check for infinite loops,
so it could remove them.
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@kripken
kripken authored May 29, 2024
1 parent b85197c commit 5d90167
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Showing 2 changed files with 46 additions and 26 deletions.
9 changes: 5 additions & 4 deletions src/passes/Vacuum.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -158,15 +158,16 @@ struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
continue;
}

// Check if we may no longer be heading to a trap. Two situations count
// here: Control flow might branch, or we might call (since a call might
// reach an import; see notes on that in pass.h:trapsNeverHappen).
// Check if we may no longer be heading to a trap. We can only optimize
// if the trap will actually be reached. Two situations can prevent that
// here: Control flow might branch away, or we might hang (which can
// happen in a call or a loop).
//
// We also cannot remove a pop as it is necessary for structural
// reasons.
EffectAnalyzer effects(getPassOptions(), *getModule(), list[i]);
if (effects.transfersControlFlow() || effects.calls ||
effects.danglingPop) {
effects.mayNotReturn || effects.danglingPop) {
headingToTrap = false;
continue;
}
Expand Down
63 changes: 41 additions & 22 deletions test/lit/passes/vacuum-tnh.wast
View file
Original file line number Diff line number Diff line change
Expand Up @@ -117,10 +117,10 @@
)

;; A helper function for the above, that returns nothing.
;; YESTNH: (func $return-nothing (type $1)
;; YESTNH: (func $return-nothing (type $0)
;; YESTNH-NEXT: (nop)
;; YESTNH-NEXT: )
;; NO_TNH: (func $return-nothing (type $1)
;; NO_TNH: (func $return-nothing (type $0)
;; NO_TNH-NEXT: (nop)
;; NO_TNH-NEXT: )
(func $return-nothing)
Expand Down Expand Up @@ -179,10 +179,10 @@
(local.get $y)
)

;; YESTNH: (func $toplevel (type $1)
;; YESTNH: (func $toplevel (type $0)
;; YESTNH-NEXT: (nop)
;; YESTNH-NEXT: )
;; NO_TNH: (func $toplevel (type $1)
;; NO_TNH: (func $toplevel (type $0)
;; NO_TNH-NEXT: (unreachable)
;; NO_TNH-NEXT: )
(func $toplevel
Expand All @@ -191,7 +191,7 @@
(unreachable)
)

;; YESTNH: (func $drop-loop (type $1)
;; YESTNH: (func $drop-loop (type $0)
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (loop $loop (result i32)
;; YESTNH-NEXT: (br_if $loop
Expand All @@ -201,7 +201,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $drop-loop (type $1)
;; NO_TNH: (func $drop-loop (type $0)
;; NO_TNH-NEXT: (drop
;; NO_TNH-NEXT: (loop $loop (result i32)
;; NO_TNH-NEXT: (br_if $loop
Expand All @@ -224,7 +224,7 @@
)
)

;; YESTNH: (func $loop-effects (type $1)
;; YESTNH: (func $loop-effects (type $0)
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (loop $loop (result i32)
;; YESTNH-NEXT: (drop
Expand All @@ -239,7 +239,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $loop-effects (type $1)
;; NO_TNH: (func $loop-effects (type $0)
;; NO_TNH-NEXT: (drop
;; NO_TNH-NEXT: (loop $loop (result i32)
;; NO_TNH-NEXT: (drop
Expand Down Expand Up @@ -272,7 +272,7 @@
)
)

;; YESTNH: (func $if-unreachable (type $0) (param $p i32)
;; YESTNH: (func $if-unreachable (type $1) (param $p i32)
;; YESTNH-NEXT: (drop
;; YESTNH-NEXT: (local.get $p)
;; YESTNH-NEXT: )
Expand All @@ -294,7 +294,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $if-unreachable (type $0) (param $p i32)
;; NO_TNH: (func $if-unreachable (type $1) (param $p i32)
;; NO_TNH-NEXT: (if
;; NO_TNH-NEXT: (local.get $p)
;; NO_TNH-NEXT: (then
Expand Down Expand Up @@ -415,7 +415,7 @@
)
)

;; YESTNH: (func $block-unreachable (type $0) (param $p i32)
;; YESTNH: (func $block-unreachable (type $1) (param $p i32)
;; YESTNH-NEXT: (if
;; YESTNH-NEXT: (local.get $p)
;; YESTNH-NEXT: (then
Expand All @@ -433,7 +433,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $block-unreachable (type $0) (param $p i32)
;; NO_TNH: (func $block-unreachable (type $1) (param $p i32)
;; NO_TNH-NEXT: (if
;; NO_TNH-NEXT: (local.get $p)
;; NO_TNH-NEXT: (then
Expand Down Expand Up @@ -482,7 +482,7 @@
)
)

;; YESTNH: (func $block-unreachable-named (type $0) (param $p i32)
;; YESTNH: (func $block-unreachable-named (type $1) (param $p i32)
;; YESTNH-NEXT: (if
;; YESTNH-NEXT: (local.get $p)
;; YESTNH-NEXT: (then
Expand All @@ -499,7 +499,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $block-unreachable-named (type $0) (param $p i32)
;; NO_TNH: (func $block-unreachable-named (type $1) (param $p i32)
;; NO_TNH-NEXT: (if
;; NO_TNH-NEXT: (local.get $p)
;; NO_TNH-NEXT: (then
Expand Down Expand Up @@ -544,10 +544,10 @@
)
)

;; YESTNH: (func $block-unreachable-all (type $0) (param $p i32)
;; YESTNH: (func $block-unreachable-all (type $1) (param $p i32)
;; YESTNH-NEXT: (nop)
;; YESTNH-NEXT: )
;; NO_TNH: (func $block-unreachable-all (type $0) (param $p i32)
;; NO_TNH: (func $block-unreachable-all (type $1) (param $p i32)
;; NO_TNH-NEXT: (if
;; NO_TNH-NEXT: (local.get $p)
;; NO_TNH-NEXT: (then
Expand Down Expand Up @@ -584,15 +584,15 @@
)
)

;; YESTNH: (func $block-unreachable-but-call (type $1)
;; YESTNH: (func $block-unreachable-but-call (type $0)
;; YESTNH-NEXT: (i32.store
;; YESTNH-NEXT: (i32.const 0)
;; YESTNH-NEXT: (i32.const 1)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: (call $block-unreachable-but-call)
;; YESTNH-NEXT: (unreachable)
;; YESTNH-NEXT: )
;; NO_TNH: (func $block-unreachable-but-call (type $1)
;; NO_TNH: (func $block-unreachable-but-call (type $0)
;; NO_TNH-NEXT: (i32.store
;; NO_TNH-NEXT: (i32.const 0)
;; NO_TNH-NEXT: (i32.const 1)
Expand Down Expand Up @@ -620,7 +620,7 @@
(unreachable)
)

;; YESTNH: (func $catch-pop (type $1)
;; YESTNH: (func $catch-pop (type $0)
;; YESTNH-NEXT: (try $try
;; YESTNH-NEXT: (do
;; YESTNH-NEXT: (call $catch-pop)
Expand All @@ -633,7 +633,7 @@
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $catch-pop (type $1)
;; NO_TNH: (func $catch-pop (type $0)
;; NO_TNH-NEXT: (try $try
;; NO_TNH-NEXT: (do
;; NO_TNH-NEXT: (call $catch-pop)
Expand Down Expand Up @@ -673,7 +673,7 @@
)
)

;; YESTNH: (func $loop-unreachable (type $0) (param $p i32)
;; YESTNH: (func $loop-unreachable (type $1) (param $p i32)
;; YESTNH-NEXT: (loop $loop
;; YESTNH-NEXT: (i32.store
;; YESTNH-NEXT: (i32.const 0)
Expand All @@ -688,7 +688,7 @@
;; YESTNH-NEXT: (unreachable)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $loop-unreachable (type $0) (param $p i32)
;; NO_TNH: (func $loop-unreachable (type $1) (param $p i32)
;; NO_TNH-NEXT: (loop $loop
;; NO_TNH-NEXT: (i32.store
;; NO_TNH-NEXT: (i32.const 0)
Expand Down Expand Up @@ -728,4 +728,23 @@
(unreachable)
)
)

;; YESTNH: (func $unreached-infinite-loop (type $0)
;; YESTNH-NEXT: (loop $label$1
;; YESTNH-NEXT: (br $label$1)
;; YESTNH-NEXT: )
;; YESTNH-NEXT: )
;; NO_TNH: (func $unreached-infinite-loop (type $0)
;; NO_TNH-NEXT: (loop $label$1
;; NO_TNH-NEXT: (br $label$1)
;; NO_TNH-NEXT: )
;; NO_TNH-NEXT: )
(func $unreached-infinite-loop
;; Code that reaches an unreachable can be removed in TNH mode, but an
;; infinite loop may not reach it, so nothing can be removed here.
(loop $label$1
(br $label$1)
)
(unreachable)
)
)

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