diff options
| -rw-r--r-- | src/passes/DeadCodeElimination.cpp | 91 |
1 files changed, 34 insertions, 57 deletions
diff --git a/src/passes/DeadCodeElimination.cpp b/src/passes/DeadCodeElimination.cpp index 42f86ba45..af06439c0 100644 --- a/src/passes/DeadCodeElimination.cpp +++ b/src/passes/DeadCodeElimination.cpp @@ -76,11 +76,16 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> } } - // if a child is unreachable, we can replace ourselves with it + // if a child exists and is unreachable, we can replace ourselves with it bool isDead(Expression* child) { return child && child->type == unreachable; } + // a similar check, assumes the child exists + bool isUnreachable(Expression* child) { + return child->type == unreachable; + } + // things that stop control flow void visitBreak(Break* curr) { @@ -117,7 +122,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> replaceCurrent(curr->value); return; } - if (isDead(curr->condition)) { + if (isUnreachable(curr->condition)) { if (curr->value) { auto* block = getModule()->allocator.alloc<Block>(); block->list.resize(2); @@ -149,45 +154,25 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> reachable = false; } - // we maintain a stack for blocks, as we visit each item, and the parameter is the index - - std::vector<Index> blockStack; // index in current block - - static void doPreBlock(DeadCodeElimination* self, Expression** currp) { - self->blockStack.push_back(0); - } - - static void doAfterBlockElement(DeadCodeElimination* self, Expression** currp) { - auto* block = (*currp)->cast<Block>(); - Index i = self->blockStack.back(); - self->blockStack.back()++; - if (!self->reachable) { - // control flow ended in the middle of the block, so we can truncate the rest. - // note that we still visit the rest, so if we already truncated, do not lengthen. - // note that it is ok that we visit the others even though the list was shortened; - // our arena vectors leave things as they are when shrinking. - if (block->list.size() > i + 1) { - // but note that it is not legal to truncate a block if it leaves a bad last element, - // given the wasm type rules. For example, if the last element is a return, then - // the block doesn't care about it for type checking purposes, but if removing - // it would leave an element with type none as the last, that could be a problem, - // see https://github.com/WebAssembly/spec/issues/355 - if (!(isConcreteWasmType(block->type) && block->list[i]->type == none)) { - block->list.resize(i + 1); - // note that we still walk the children, so typeUpdater will already - // note they are being removed, and we don't need to do that here + void visitBlock(Block* curr) { + auto& list = curr->list; + // if we are currently unreachable (before we take into account + // breaks to the block) then a child may be unreachable, and we + // can shorten + if (!reachable && list.size() > 1) { + // to do here: nothing to remove after it) + for (Index i = 0; i < list.size() - 1; i++) { + if (list[i]->type == unreachable) { + list.resize(i + 1); + break; } } } - } - - void visitBlock(Block* curr) { - blockStack.pop_back(); if (curr->name.is()) { reachable = reachable || reachableBreaks.count(curr->name); reachableBreaks.erase(curr->name); } - if (curr->list.size() == 1 && isDead(curr->list[0])) { + if (list.size() == 1 && isUnreachable(list[0])) { replaceCurrent(BlockUtils::simplifyToContentsWithPossibleTypeChange(curr, this)); } else { // the block may have had a type, but can now be unreachable, which allows more reduction outside @@ -199,7 +184,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> if (curr->name.is()) { reachableBreaks.erase(curr->name); } - if (isDead(curr->body) && !BreakSeeker::has(curr->body, curr->name)) { + if (isUnreachable(curr->body) && !BreakSeeker::has(curr->body, curr->name)) { replaceCurrent(curr->body); return; } @@ -225,7 +210,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> // the ifStack has the branch that joins us, either from before if just an if, or the ifTrue if an if-else reachable = reachable || ifStack.back(); ifStack.pop_back(); - if (isDead(curr->condition)) { + if (isUnreachable(curr->condition)) { replaceCurrent(curr->condition); } // the if may have had a type, but can now be unreachable, which allows more reduction outside @@ -280,14 +265,6 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> self->pushTask(DeadCodeElimination::scan, &curr->cast<If>()->ifTrue); self->pushTask(DeadCodeElimination::doAfterIfCondition, currp); self->pushTask(DeadCodeElimination::scan, &curr->cast<If>()->condition); - } else if (curr->is<Block>()) { - self->pushTask(DeadCodeElimination::doVisitBlock, currp); - auto& list = curr->cast<Block>()->list; - for (int i = int(list.size()) - 1; i >= 0; i--) { - self->pushTask(DeadCodeElimination::doAfterBlockElement, currp); - self->pushTask(DeadCodeElimination::scan, &list[i]); - } - self->pushTask(DeadCodeElimination::doPreBlock, currp); } else { WalkerPass<PostWalker<DeadCodeElimination>>::scan(self, currp); } @@ -304,7 +281,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> template<typename T> Expression* handleCall(T* curr) { for (Index i = 0; i < curr->operands.size(); i++) { - if (isDead(curr->operands[i])) { + if (isUnreachable(curr->operands[i])) { if (i > 0) { auto* block = getModule()->allocator.alloc<Block>(); Index newSize = i + 1; @@ -333,7 +310,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> void visitCallIndirect(CallIndirect* curr) { if (handleCall(curr) != curr) return; - if (isDead(curr->target)) { + if (isUnreachable(curr->target)) { auto* block = getModule()->allocator.alloc<Block>(); for (auto* operand : curr->operands) { block->list.push_back(drop(operand)); @@ -345,23 +322,23 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> } void visitSetLocal(SetLocal* curr) { - if (isDead(curr->value)) { + if (isUnreachable(curr->value)) { replaceCurrent(curr->value); } } void visitLoad(Load* curr) { - if (isDead(curr->ptr)) { + if (isUnreachable(curr->ptr)) { replaceCurrent(curr->ptr); } } void visitStore(Store* curr) { - if (isDead(curr->ptr)) { + if (isUnreachable(curr->ptr)) { replaceCurrent(curr->ptr); return; } - if (isDead(curr->value)) { + if (isUnreachable(curr->value)) { auto* block = getModule()->allocator.alloc<Block>(); block->list.resize(2); block->list[0] = drop(curr->ptr); @@ -372,17 +349,17 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> } void visitUnary(Unary* curr) { - if (isDead(curr->value)) { + if (isUnreachable(curr->value)) { replaceCurrent(curr->value); } } void visitBinary(Binary* curr) { - if (isDead(curr->left)) { + if (isUnreachable(curr->left)) { replaceCurrent(curr->left); return; } - if (isDead(curr->right)) { + if (isUnreachable(curr->right)) { auto* block = getModule()->allocator.alloc<Block>(); block->list.resize(2); block->list[0] = drop(curr->left); @@ -393,11 +370,11 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> } void visitSelect(Select* curr) { - if (isDead(curr->ifTrue)) { + if (isUnreachable(curr->ifTrue)) { replaceCurrent(curr->ifTrue); return; } - if (isDead(curr->ifFalse)) { + if (isUnreachable(curr->ifFalse)) { auto* block = getModule()->allocator.alloc<Block>(); block->list.resize(2); block->list[0] = drop(curr->ifTrue); @@ -406,7 +383,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> replaceCurrent(block); return; } - if (isDead(curr->condition)) { + if (isUnreachable(curr->condition)) { auto* block = getModule()->allocator.alloc<Block>(); block->list.resize(3); block->list[0] = drop(curr->ifTrue); @@ -419,7 +396,7 @@ struct DeadCodeElimination : public WalkerPass<PostWalker<DeadCodeElimination>> } void visitDrop(Drop* curr) { - if (isDead(curr->value)) { + if (isUnreachable(curr->value)) { replaceCurrent(curr->value); } } |