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Add EH support for CFGWalker (#2597)
This adds EH instruction support for `CFGWalker`. This also implements `call` instruction handling within a try-catch; every call can possibly throw and unwind to the innermost catch block. This adds tests for RedundantSetElimination pass, which uses `CFGWalker`.
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‎src/cfg/cfg-traversal.h‎

Lines changed: 84 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -64,8 +64,15 @@ struct CFGWalker : public ControlFlowWalker<SubType, VisitorType> {
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BasicBlock* currBasicBlock;
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// a block or loop => its branches
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std::map<Expression*, std::vector<BasicBlock*>> branches;
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// stack of the last blocks of if conditions + the last blocks of if true
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// bodies
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std::vector<BasicBlock*> ifStack;
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// stack of the first blocks of loops
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std::vector<BasicBlock*> loopStack;
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// stack of the last blocks of try bodies
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std::vector<BasicBlock*> tryStack;
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// stack of the first blocks of catch bodies
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std::vector<BasicBlock*> catchStack;
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7077
void startBasicBlock() {
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currBasicBlock = ((SubType*)this)->makeBasicBlock();
@@ -198,6 +205,59 @@ struct CFGWalker : public ControlFlowWalker<SubType, VisitorType> {
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self->startUnreachableBlock();
199206
}
200207

208+
static void doEndCall(SubType* self, Expression** currp) {
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// Every call can possibly throw, but we don't end the current basic block
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// unless the call is within a try-catch, because the CFG will have too many
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// blocks that way, and if an exception is thrown, the function will be
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// exited anyway.
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if (!self->catchStack.empty()) {
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auto* last = self->currBasicBlock;
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self->startBasicBlock();
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self->link(last, self->currBasicBlock); // exception not thrown
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self->link(last, self->catchStack.back()); // exception thrown
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}
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}
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static void doStartTry(SubType* self, Expression** currp) {
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auto* last = self->currBasicBlock;
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self->startBasicBlock(); // catch body's first block
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self->catchStack.push_back(self->currBasicBlock);
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self->currBasicBlock = last; // reset to the current block
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}
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static void doStartCatch(SubType* self, Expression** currp) {
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self->tryStack.push_back(self->currBasicBlock); // last block of try body
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self->currBasicBlock = self->catchStack.back();
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self->catchStack.pop_back();
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}
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static void doEndTry(SubType* self, Expression** currp) {
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auto* last = self->currBasicBlock;
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self->startBasicBlock(); // continuation block after try-catch
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// catch body's last block -> continuation block
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self->link(last, self->currBasicBlock);
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// try body's last block -> continuation block
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self->link(self->tryStack.back(), self->currBasicBlock);
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self->tryStack.pop_back();
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}
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static void doEndThrow(SubType* self, Expression** currp) {
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// We unwind to the innermost catch, if any
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if (!self->catchStack.empty()) {
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self->link(self->currBasicBlock, self->catchStack.back());
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}
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self->startUnreachableBlock();
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}
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static void doEndBrOnExn(SubType* self, Expression** currp) {
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auto* curr = (*currp)->cast<BrOnExn>();
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self->branches[self->findBreakTarget(curr->name)].push_back(
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self->currBasicBlock); // branch to the target
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auto* last = self->currBasicBlock;
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self->startBasicBlock();
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self->link(last, self->currBasicBlock); // we might fall through
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}
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static void scan(SubType* self, Expression** currp) {
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Expression* curr = *currp;
203263

@@ -238,6 +298,28 @@ struct CFGWalker : public ControlFlowWalker<SubType, VisitorType> {
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self->pushTask(SubType::doStartUnreachableBlock, currp);
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break;
240300
}
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case Expression::Id::CallId:
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case Expression::Id::CallIndirectId: {
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self->pushTask(SubType::doEndCall, currp);
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break;
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}
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case Expression::Id::TryId: {
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self->pushTask(SubType::doEndTry, currp);
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self->pushTask(SubType::scan, &curr->cast<Try>()->catchBody);
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self->pushTask(SubType::doStartCatch, currp);
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self->pushTask(SubType::scan, &curr->cast<Try>()->body);
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self->pushTask(SubType::doStartTry, currp);
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return; // don't do anything else
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}
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case Expression::Id::ThrowId:
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case Expression::Id::RethrowId: {
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self->pushTask(SubType::doEndThrow, currp);
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break;
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}
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case Expression::Id::BrOnExnId: {
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self->pushTask(SubType::doEndBrOnExn, currp);
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break;
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}
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default: {}
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}
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@@ -263,6 +345,8 @@ struct CFGWalker : public ControlFlowWalker<SubType, VisitorType> {
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assert(branches.size() == 0);
264346
assert(ifStack.size() == 0);
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assert(loopStack.size() == 0);
348+
assert(tryStack.size() == 0);
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assert(catchStack.size() == 0);
266350
}
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268352
std::unordered_set<BasicBlock*> findLiveBlocks() {

‎test/passes/rse.txt‎ renamed to ‎test/passes/rse_all-features.txt‎

Lines changed: 125 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,7 @@
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(type $i32_=>_none (func (param i32)))
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(type $i32_i32_=>_none (func (param i32 i32)))
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(type $i32_f64_=>_none (func (param i32 f64)))
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(event $e (attr 0) (param i32))
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(func $basic (; 0 ;) (param $x i32) (param $y f64)
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(local $a f32)
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(local $b i64)
@@ -459,4 +460,128 @@
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)
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)
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)
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(func $try1 (; 19 ;)
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(local $x i32)
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(try
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(nop)
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(catch
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(drop
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(exnref.pop)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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(func $try2 (; 20 ;)
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(local $x i32)
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(try
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(block $block
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(throw $e
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(i32.const 0)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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(catch
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(drop
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(exnref.pop)
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)
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)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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(func $try3 (; 21 ;)
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(local $x i32)
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(try
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(throw $e
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(i32.const 0)
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)
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(catch
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(drop
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(exnref.pop)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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)
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(drop
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(i32.const 1)
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)
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)
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(func $foo (; 22 ;)
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(nop)
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)
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(func $try4 (; 23 ;)
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(local $x i32)
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(try
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(block $block
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(call $foo)
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(local.set $x
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(i32.const 1)
530+
)
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)
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(catch
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(drop
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(exnref.pop)
535+
)
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)
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)
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(local.set $x
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(i32.const 1)
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)
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)
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(func $try5 (; 24 ;)
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(local $x i32)
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(try
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(block $block
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(local.set $x
547+
(i32.const 1)
548+
)
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(call $foo)
550+
)
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(catch
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(drop
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(exnref.pop)
554+
)
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)
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)
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(drop
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(i32.const 1)
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)
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)
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(func $nested-try (; 25 ;)
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(local $x i32)
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(try
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(try
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(throw $e
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(i32.const 0)
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)
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(catch
569+
(rethrow
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(exnref.pop)
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)
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)
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)
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(catch
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(drop
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(exnref.pop)
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)
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(local.set $x
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(i32.const 1)
580+
)
581+
)
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)
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(drop
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(i32.const 1)
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)
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)
462587
)

‎test/passes/rse.wast‎ renamed to ‎test/passes/rse_all-features.wast‎

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Original file line numberDiff line numberDiff line change
@@ -277,5 +277,84 @@
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)
278278
)
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)
280+
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(event $e (attr 0) (param i32))
282+
(func $try1
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(local $x i32)
284+
(try
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(catch
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(drop (exnref.pop))
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(local.set $x (i32.const 1))
288+
)
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)
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(local.set $x (i32.const 1)) ;; should NOT be dropped
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)
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(func $try2
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(local $x i32)
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(try
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(block
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(throw $e (i32.const 0))
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(local.set $x (i32.const 1))
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)
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(catch
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(drop (exnref.pop))
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)
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)
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(local.set $x (i32.const 1)) ;; should NOT be dropped
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)
305+
(func $try3
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(local $x i32)
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(try
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(throw $e (i32.const 0))
309+
(catch
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(drop (exnref.pop))
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(local.set $x (i32.const 1))
312+
)
313+
)
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(local.set $x (i32.const 1)) ;; should be dropped
315+
)
316+
(func $foo)
317+
(func $try4
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(local $x i32)
319+
(try
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(block
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(call $foo)
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(local.set $x (i32.const 1))
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)
324+
(catch
325+
(drop (exnref.pop))
326+
)
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)
328+
(local.set $x (i32.const 1)) ;; should NOT be dropped
329+
)
330+
(func $try5
331+
(local $x i32)
332+
(try
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(block
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(local.set $x (i32.const 1))
335+
(call $foo)
336+
)
337+
(catch
338+
(drop (exnref.pop))
339+
)
340+
)
341+
(local.set $x (i32.const 1)) ;; should be dropped
342+
)
343+
(func $nested-try
344+
(local $x i32)
345+
(try
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(try
347+
(throw $e (i32.const 0))
348+
(catch
349+
(rethrow (exnref.pop))
350+
)
351+
)
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(catch
353+
(drop (exnref.pop))
354+
(local.set $x (i32.const 1))
355+
)
356+
)
357+
(local.set $x (i32.const 1)) ;; should be dropped
358+
)
280359
)
281360

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