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[EH] Fix missing outer block for catchless try #6519

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Merged
aheejin merged 4 commits into from
Apr 23, 2024
Merged

[EH] Fix missing outer block for catchless try #6519

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7ab52bc
[EH] Fix missing outer block for catchless try
aheejin Apr 21, 2024
8c8fcc5
Remove unused outer block
aheejin Apr 23, 2024
7553742
clang-format
aheejin Apr 23, 2024
5a81dea
Merge branch 'main' into translate_fix_outerblock
aheejin Apr 23, 2024
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10 changes: 9 additions & 1 deletion src/passes/TranslateEH.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -385,7 +385,15 @@ struct TranslateToNewEH : public WalkerPass<PostWalker<TranslateToNewEH>> {

// If we don't have any catches, we don't need to do more.
if (curr->catchBodies.empty()) { // catch-less try
replaceCurrent(tryTable);
// If we need an outer block for other reasons (if this is a target of a
// delegate), we insert the new try_table into it. If not we just replace
// the current try with the new try_table.
if (outerBlock) {
outerBlock->list.push_back(tryTable);
replaceCurrent(outerBlock);
} else {
replaceCurrent(tryTable);
}
return;
}

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55 changes: 49 additions & 6 deletions test/lit/passes/translate-to-new-eh.wast
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Expand Up @@ -1788,13 +1788,15 @@
)

;; CHECK: (func $deletate-target-outer-try-unreachable (type $1)
;; CHECK-NEXT: (try_table
;; CHECK-NEXT: (throw_ref
;; CHECK-NEXT: (block $l00 (result exnref)
;; CHECK-NEXT: (try_table (catch_all_ref $l00)
;; CHECK-NEXT: (call $foo)
;; CHECK-NEXT: (block $outer1
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@kripken kripken Apr 22, 2024

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Why was this outer block needed?

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@aheejin aheejin Apr 23, 2024

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Before we go into actually processing catches and delegates, we create an outer block in this condition:

binaryen/src/passes/TranslateEH.cpp

Line 677 in 219e668

if (it != delegateTargetToBrTarget.end() || curr->isCatch()) {

Because

  1. In case of a delegate, it will be translated into a throw_ref to the delegate target. But when an exception does not occur, we have to bail out of that throw_ref. And this outer block is that bail-out destination. It is explained here:

    binaryen/src/passes/TranslateEH.cpp

    Line 251 in e50a2ba

    // (br $outer)

    binaryen/src/passes/TranslateEH.cpp

    Line 267 in e50a2ba

    // (br $outer ;; Now has the try_table as a child.

  2. In case of catches, we proceed into catch handler parts unless we bail out in case an exception does not occur. It is explained here:

    binaryen/src/passes/TranslateEH.cpp

    Line 415 in e50a2ba

    // (br $outer)

    binaryen/src/passes/TranslateEH.cpp

    Line 436 in e50a2ba

    // (br $outer

But this test does not need a br because the body's type is unreachable due to a return. We omit that br here:

binaryen/src/passes/TranslateEH.cpp

Lines 298 to 300 in e50a2ba

auto* brToOuter = curr->body->type == Type::unreachable
? nullptr
: builder.makeBreak(outerBlock->name);

It is hard to check this condition before creating an outer block. We can run BranchSeeker to find out if the block is actually used as a destination for a branch afterwards to remove this unnecessary block. Do you want me to do that? It is not hard, but I didn't end up doing that because we might be adding too much optimization in this pass which should ideally be done by other passes later. Currently we run this pass at the end and don't run any other optimization passes after this, I already baked some amount of optimization into it though.

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@aheejin aheejin Apr 23, 2024

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Tried removing it without using BranchSeeker: 8c8fcc5

;; CHECK-NEXT: (try_table
;; CHECK-NEXT: (throw_ref
;; CHECK-NEXT: (block $l00 (result exnref)
;; CHECK-NEXT: (try_table (catch_all_ref $l00)
;; CHECK-NEXT: (call $foo)
;; CHECK-NEXT: )
;; CHECK-NEXT: (return)
;; CHECK-NEXT: )
;; CHECK-NEXT: (return)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand Down Expand Up @@ -2125,4 +2127,45 @@
(delegate 0)
)
)

;; CHECK: (func $try-delegate-within-catchless-try (type $1)
;; CHECK-NEXT: (block $outer1
;; CHECK-NEXT: (try_table
;; CHECK-NEXT: (throw_ref
;; CHECK-NEXT: (block $l00 (result exnref)
;; CHECK-NEXT: (try_table (catch_all_ref $l00)
;; CHECK-NEXT: (call $foo)
;; CHECK-NEXT: )
;; CHECK-NEXT: (br $outer1)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; STACKIR-OPT: (func $try-delegate-within-catchless-try (type $1)
;; STACKIR-OPT-NEXT: block $outer1
;; STACKIR-OPT-NEXT: try_table
;; STACKIR-OPT-NEXT: block $l00 (result exnref)
;; STACKIR-OPT-NEXT: try_table (catch_all_ref $l00)
;; STACKIR-OPT-NEXT: call $foo
;; STACKIR-OPT-NEXT: end
;; STACKIR-OPT-NEXT: br $outer1
;; STACKIR-OPT-NEXT: end
;; STACKIR-OPT-NEXT: throw_ref
;; STACKIR-OPT-NEXT: end
;; STACKIR-OPT-NEXT: unreachable
;; STACKIR-OPT-NEXT: end
;; STACKIR-OPT-NEXT: )
(func $try-delegate-within-catchless-try
(try $l0
(do
(try
(do
(call $foo)
)
(delegate $l0)
)
)
)
)
)