src/passes/Vacuum.cpp - external/github.com/WebAssembly/binaryen - Git at Google

 /*
  * Copyright 2016 WebAssembly Community Group participants
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 //
 // Removes obviously unneeded code
 //

 #include <wasm.h>
 #include <pass.h>
 #include <ast_utils.h>
 #include <wasm-builder.h>

 namespace wasm {

 struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
   bool isFunctionParallel() override { return true; }

   Pass* create() override { return new Vacuum; }

   // returns nullptr if curr is dead, curr if it must stay as is, or another node if it can be replaced
   Expression* optimize(Expression* curr, bool resultUsed) {
     while (1) {
       switch (curr->_id) {
         case Expression::Id::NopId: return nullptr; // never needed

         case Expression::Id::BlockId: return curr; // not always needed, but handled in visitBlock()
         case Expression::Id::IfId: return curr; // not always needed, but handled in visitIf()
         case Expression::Id::LoopId: return curr; // not always needed, but handled in visitLoop()
         case Expression::Id::DropId: return curr; // not always needed, but handled in visitDrop()

         case Expression::Id::BreakId:
         case Expression::Id::SwitchId:
         case Expression::Id::CallId:
         case Expression::Id::CallImportId:
         case Expression::Id::CallIndirectId:
         case Expression::Id::SetLocalId:
         case Expression::Id::StoreId:
         case Expression::Id::ReturnId:
         case Expression::Id::SetGlobalId:
         case Expression::Id::HostId:
         case Expression::Id::UnreachableId: return curr; // always needed

         case Expression::Id::LoadId: {
           if (!resultUsed) {
             return curr->cast<Load>()->ptr;
           }
           return curr;
         }
         case Expression::Id::ConstId:
         case Expression::Id::GetLocalId:
         case Expression::Id::GetGlobalId: {
           if (!resultUsed) return nullptr;
           return curr;
         }

         case Expression::Id::UnaryId:
         case Expression::Id::BinaryId:
         case Expression::Id::SelectId: {
           if (resultUsed) {
             return curr; // used, keep it
           }
           // for unary, binary, and select, we need to check their arguments for side effects
           if (auto* unary = curr->dynCast<Unary>()) {
             if (EffectAnalyzer(getPassOptions(), unary->value).hasSideEffects()) {
               curr = unary->value;
               continue;
             } else {
               return nullptr;
             }
           } else if (auto* binary = curr->dynCast<Binary>()) {
             if (EffectAnalyzer(getPassOptions(), binary->left).hasSideEffects()) {
               if (EffectAnalyzer(getPassOptions(), binary->right).hasSideEffects()) {
                 return curr; // leave them
               } else {
                 curr = binary->left;
                 continue;
               }
             } else {
               if (EffectAnalyzer(getPassOptions(), binary->right).hasSideEffects()) {
                 curr = binary->right;
                 continue;
               } else {
                 return nullptr;
               }
             }
           } else {
             // TODO: if two have side effects, we could replace the select with say an add?
             auto* select = curr->cast<Select>();
             if (EffectAnalyzer(getPassOptions(), select->ifTrue).hasSideEffects()) {
               if (EffectAnalyzer(getPassOptions(), select->ifFalse).hasSideEffects()) {
                 return curr; // leave them
               } else {
                 if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
                   return curr; // leave them
                 } else {
                   curr = select->ifTrue;
                   continue;
                 }
               }
             } else {
               if (EffectAnalyzer(getPassOptions(), select->ifFalse).hasSideEffects()) {
                 if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
                   return curr; // leave them
                 } else {
                   curr = select->ifFalse;
                   continue;
                 }
               } else {
                 if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
                   curr = select->condition;
                   continue;
                 } else {
                   return nullptr;
                 }
               }
             }
           }
         }

         default: WASM_UNREACHABLE();
       }
     }
   }

   void visitBlock(Block *curr) {
     // compress out nops and other dead code
     int skip = 0;
     auto& list = curr->list;
     size_t size = list.size();
     bool needResize = false;
     for (size_t z = 0; z < size; z++) {
       auto* optimized = optimize(list[z], z == size - 1 && isConcreteWasmType(curr->type));
       if (!optimized) {
         skip++;
         needResize = true;
       } else {
         if (optimized != list[z]) {
           list[z] = optimized;
         }
         if (skip > 0) {
           list[z - skip] = list[z];
         }
         // if this is an unconditional br, the rest is dead code
         Break* br = list[z - skip]->dynCast<Break>();
         Switch* sw = list[z - skip]->dynCast<Switch>();
         if ((br && !br->condition) || sw) {
           auto* last = list.back();
           list.resize(z - skip + 1);
           // if we removed the last one, and it was a return value, it must be returned
           if (list.back() != last && isConcreteWasmType(last->type)) {
             list.push_back(last);
           }
           needResize = false;
           break;
         }
       }
     }
     if (needResize) {
       list.resize(size - skip);
     }
     if (!curr->name.is()) {
       if (list.size() == 1) {
         // just one element. replace the block, either with it or with a nop if it's not needed
         if (isConcreteWasmType(curr->type) || EffectAnalyzer(getPassOptions(), list[0]).hasSideEffects()) {
           replaceCurrent(list[0]);
         } else {
           if (curr->type == unreachable) {
             ExpressionManipulator::convert<Block, Unreachable>(curr);
           } else {
             ExpressionManipulator::nop(curr);
           }
         }
       } else if (list.size() == 0) {
         ExpressionManipulator::nop(curr);
       }
     }
   }

   void visitIf(If* curr) {
     // if the condition is a constant, just apply it
     // we can just return the ifTrue or ifFalse.
     if (auto* value = curr->condition->dynCast<Const>()) {
       if (value->value.getInteger()) {
         replaceCurrent(curr->ifTrue);
         return;
       } else {
         if (curr->ifFalse) {
           replaceCurrent(curr->ifFalse);
         } else {
           ExpressionManipulator::nop(curr);
         }
         return;
       }
     }
     if (curr->ifFalse) {
       if (curr->ifFalse->is<Nop>()) {
         curr->ifFalse = nullptr;
       } else if (curr->ifTrue->is<Nop>()) {
         curr->ifTrue = curr->ifFalse;
         curr->ifFalse = nullptr;
         curr->condition = Builder(*getModule()).makeUnary(EqZInt32, curr->condition);
       } else if (curr->ifTrue->is<Drop>() && curr->ifFalse->is<Drop>()) {
         // instead of dropping both sides, drop the if, if they are the same type
         auto* left = curr->ifTrue->cast<Drop>()->value;
         auto* right = curr->ifFalse->cast<Drop>()->value;
         if (left->type == right->type) {
           curr->ifTrue = left;
           curr->ifFalse = right;
           curr->finalize();
           replaceCurrent(Builder(*getModule()).makeDrop(curr));
         }
       }
     } else {
       // no else
       if (curr->ifTrue->is<Nop>()) {
         // no nothing
         replaceCurrent(Builder(*getModule()).makeDrop(curr->condition));
       }
     }
   }

   void visitLoop(Loop* curr) {
     if (curr->body->is<Nop>()) ExpressionManipulator::nop(curr);
   }

   void visitDrop(Drop* curr) {
     // optimize the dropped value, maybe leaving nothing
     curr->value = optimize(curr->value, false);
     if (curr->value == nullptr) {
       ExpressionManipulator::nop(curr);
       return;
     }
     // a drop of a tee is a set
     if (auto* set = curr->value->dynCast<SetLocal>()) {
       assert(set->isTee());
       set->setTee(false);
       replaceCurrent(set);
       return;
     }
     // if we are dropping a block's return value, we might be able to remove it entirely
     if (auto* block = curr->value->dynCast<Block>()) {
       auto* last = block->list.back();
       if (isConcreteWasmType(last->type)) {
         assert(block->type == last->type);
         last = optimize(last, false);
         if (!last) {
           // we may be able to remove this, if there are no brs
           bool canPop = true;
           if (block->name.is()) {
             BreakSeeker breakSeeker(block->name);
             Expression* temp = block;
             breakSeeker.walk(temp);
             if (breakSeeker.found && breakSeeker.valueType != none) {
               canPop = false;
             }
           }
           if (canPop) {
             block->list.back() = last;
             block->list.pop_back();
             block->type = none;
             // we don't need the drop anymore, let's see what we have left in the block
             if (block->list.size() > 1) {
               replaceCurrent(block);
             } else if (block->list.size() == 1) {
               replaceCurrent(block->list[0]);
             } else {
               ExpressionManipulator::nop(curr);
             }
             return;
           }
         }
       }
     }
     // sink a drop into an arm of an if-else if the other arm ends in an unreachable, as it if is a branch, this can make that branch optimizable and more vaccuming possible
     auto* iff = curr->value->dynCast<If>();
     if (iff && iff->ifFalse && isConcreteWasmType(iff->type)) {
       // reuse the drop in both cases
       if (iff->ifTrue->type == unreachable) {
         assert(isConcreteWasmType(iff->ifFalse->type));
         curr->value = iff->ifFalse;
         iff->ifFalse = curr;
         iff->type = none;
         replaceCurrent(iff);
       } else if (iff->ifFalse->type == unreachable) {
         assert(isConcreteWasmType(iff->ifTrue->type));
         curr->value = iff->ifTrue;
         iff->ifTrue = curr;
         iff->type = none;
         replaceCurrent(iff);
       }
     }
   }

   void visitFunction(Function* curr) {
     auto* optimized = optimize(curr->body, curr->result != none);
     if (optimized) {
       curr->body = optimized;
     } else {
       ExpressionManipulator::nop(curr->body);
     }
     if (curr->result == none && !EffectAnalyzer(getPassOptions(), curr->body).hasSideEffects()) {
       ExpressionManipulator::nop(curr->body);
     }
   }
 };

 Pass *createVacuumPass() {
   return new Vacuum();
 }

 } // namespace wasm
	/*
	* Copyright 2016 WebAssembly Community Group participants
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	//
	// Removes obviously unneeded code
	//

	#include <wasm.h>
	#include <pass.h>
	#include <ast_utils.h>
	#include <wasm-builder.h>

	namespace wasm {

	struct Vacuum : public WalkerPass<ExpressionStackWalker<Vacuum>> {
	bool isFunctionParallel() override { return true; }

	Pass* create() override { return new Vacuum; }

	// returns nullptr if curr is dead, curr if it must stay as is, or another node if it can be replaced
	Expression* optimize(Expression* curr, bool resultUsed) {
	while (1) {
	switch (curr->_id) {
	case Expression::Id::NopId: return nullptr; // never needed

	case Expression::Id::BlockId: return curr; // not always needed, but handled in visitBlock()
	case Expression::Id::IfId: return curr; // not always needed, but handled in visitIf()
	case Expression::Id::LoopId: return curr; // not always needed, but handled in visitLoop()
	case Expression::Id::DropId: return curr; // not always needed, but handled in visitDrop()

	case Expression::Id::BreakId:
	case Expression::Id::SwitchId:
	case Expression::Id::CallId:
	case Expression::Id::CallImportId:
	case Expression::Id::CallIndirectId:
	case Expression::Id::SetLocalId:
	case Expression::Id::StoreId:
	case Expression::Id::ReturnId:
	case Expression::Id::SetGlobalId:
	case Expression::Id::HostId:
	case Expression::Id::UnreachableId: return curr; // always needed

	case Expression::Id::LoadId: {
	if (!resultUsed) {
	return curr->cast<Load>()->ptr;
	}
	return curr;
	}
	case Expression::Id::ConstId:
	case Expression::Id::GetLocalId:
	case Expression::Id::GetGlobalId: {
	if (!resultUsed) return nullptr;
	return curr;
	}

	case Expression::Id::UnaryId:
	case Expression::Id::BinaryId:
	case Expression::Id::SelectId: {
	if (resultUsed) {
	return curr; // used, keep it
	}
	// for unary, binary, and select, we need to check their arguments for side effects
	if (auto* unary = curr->dynCast<Unary>()) {
	if (EffectAnalyzer(getPassOptions(), unary->value).hasSideEffects()) {
	curr = unary->value;
	continue;
	} else {
	return nullptr;
	}
	} else if (auto* binary = curr->dynCast<Binary>()) {
	if (EffectAnalyzer(getPassOptions(), binary->left).hasSideEffects()) {
	if (EffectAnalyzer(getPassOptions(), binary->right).hasSideEffects()) {
	return curr; // leave them
	} else {
	curr = binary->left;
	continue;
	}
	} else {
	if (EffectAnalyzer(getPassOptions(), binary->right).hasSideEffects()) {
	curr = binary->right;
	continue;
	} else {
	return nullptr;
	}
	}
	} else {
	// TODO: if two have side effects, we could replace the select with say an add?
	auto* select = curr->cast<Select>();
	if (EffectAnalyzer(getPassOptions(), select->ifTrue).hasSideEffects()) {
	if (EffectAnalyzer(getPassOptions(), select->ifFalse).hasSideEffects()) {
	return curr; // leave them
	} else {
	if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
	return curr; // leave them
	} else {
	curr = select->ifTrue;
	continue;
	}
	}
	} else {
	if (EffectAnalyzer(getPassOptions(), select->ifFalse).hasSideEffects()) {
	if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
	return curr; // leave them
	} else {
	curr = select->ifFalse;
	continue;
	}
	} else {
	if (EffectAnalyzer(getPassOptions(), select->condition).hasSideEffects()) {
	curr = select->condition;
	continue;
	} else {
	return nullptr;
	}
	}
	}
	}
	}

	default: WASM_UNREACHABLE();
	}
	}
	}

	void visitBlock(Block *curr) {
	// compress out nops and other dead code
	int skip = 0;
	auto& list = curr->list;
	size_t size = list.size();
	bool needResize = false;
	for (size_t z = 0; z < size; z++) {
	auto* optimized = optimize(list[z], z == size - 1 && isConcreteWasmType(curr->type));
	if (!optimized) {
	skip++;
	needResize = true;
	} else {
	if (optimized != list[z]) {
	list[z] = optimized;
	}
	if (skip > 0) {
	list[z - skip] = list[z];
	}
	// if this is an unconditional br, the rest is dead code
	Break* br = list[z - skip]->dynCast<Break>();
	Switch* sw = list[z - skip]->dynCast<Switch>();
	if ((br && !br->condition) \|\| sw) {
	auto* last = list.back();
	list.resize(z - skip + 1);
	// if we removed the last one, and it was a return value, it must be returned
	if (list.back() != last && isConcreteWasmType(last->type)) {
	list.push_back(last);
	}
	needResize = false;
	break;
	}
	}
	}
	if (needResize) {
	list.resize(size - skip);
	}
	if (!curr->name.is()) {
	if (list.size() == 1) {
	// just one element. replace the block, either with it or with a nop if it's not needed
	if (isConcreteWasmType(curr->type) \|\| EffectAnalyzer(getPassOptions(), list[0]).hasSideEffects()) {
	replaceCurrent(list[0]);
	} else {
	if (curr->type == unreachable) {
	ExpressionManipulator::convert<Block, Unreachable>(curr);
	} else {
	ExpressionManipulator::nop(curr);
	}
	}
	} else if (list.size() == 0) {
	ExpressionManipulator::nop(curr);
	}
	}
	}

	void visitIf(If* curr) {
	// if the condition is a constant, just apply it
	// we can just return the ifTrue or ifFalse.
	if (auto* value = curr->condition->dynCast<Const>()) {
	if (value->value.getInteger()) {
	replaceCurrent(curr->ifTrue);
	return;
	} else {
	if (curr->ifFalse) {
	replaceCurrent(curr->ifFalse);
	} else {
	ExpressionManipulator::nop(curr);
	}
	return;
	}
	}
	if (curr->ifFalse) {
	if (curr->ifFalse->is<Nop>()) {
	curr->ifFalse = nullptr;
	} else if (curr->ifTrue->is<Nop>()) {
	curr->ifTrue = curr->ifFalse;
	curr->ifFalse = nullptr;
	curr->condition = Builder(*getModule()).makeUnary(EqZInt32, curr->condition);
	} else if (curr->ifTrue->is<Drop>() && curr->ifFalse->is<Drop>()) {
	// instead of dropping both sides, drop the if, if they are the same type
	auto* left = curr->ifTrue->cast<Drop>()->value;
	auto* right = curr->ifFalse->cast<Drop>()->value;
	if (left->type == right->type) {
	curr->ifTrue = left;
	curr->ifFalse = right;
	curr->finalize();
	replaceCurrent(Builder(*getModule()).makeDrop(curr));
	}
	}
	} else {
	// no else
	if (curr->ifTrue->is<Nop>()) {
	// no nothing
	replaceCurrent(Builder(*getModule()).makeDrop(curr->condition));
	}
	}
	}

	void visitLoop(Loop* curr) {
	if (curr->body->is<Nop>()) ExpressionManipulator::nop(curr);
	}

	void visitDrop(Drop* curr) {
	// optimize the dropped value, maybe leaving nothing
	curr->value = optimize(curr->value, false);
	if (curr->value == nullptr) {
	ExpressionManipulator::nop(curr);
	return;
	}
	// a drop of a tee is a set
	if (auto* set = curr->value->dynCast<SetLocal>()) {
	assert(set->isTee());
	set->setTee(false);
	replaceCurrent(set);
	return;
	}
	// if we are dropping a block's return value, we might be able to remove it entirely
	if (auto* block = curr->value->dynCast<Block>()) {
	auto* last = block->list.back();
	if (isConcreteWasmType(last->type)) {
	assert(block->type == last->type);
	last = optimize(last, false);
	if (!last) {
	// we may be able to remove this, if there are no brs
	bool canPop = true;
	if (block->name.is()) {
	BreakSeeker breakSeeker(block->name);
	Expression* temp = block;
	breakSeeker.walk(temp);
	if (breakSeeker.found && breakSeeker.valueType != none) {
	canPop = false;
	}
	}
	if (canPop) {
	block->list.back() = last;
	block->list.pop_back();
	block->type = none;
	// we don't need the drop anymore, let's see what we have left in the block
	if (block->list.size() > 1) {
	replaceCurrent(block);
	} else if (block->list.size() == 1) {
	replaceCurrent(block->list[0]);
	} else {
	ExpressionManipulator::nop(curr);
	}
	return;
	}
	}
	}
	}
	// sink a drop into an arm of an if-else if the other arm ends in an unreachable, as it if is a branch, this can make that branch optimizable and more vaccuming possible
	auto* iff = curr->value->dynCast<If>();
	if (iff && iff->ifFalse && isConcreteWasmType(iff->type)) {
	// reuse the drop in both cases
	if (iff->ifTrue->type == unreachable) {
	assert(isConcreteWasmType(iff->ifFalse->type));
	curr->value = iff->ifFalse;
	iff->ifFalse = curr;
	iff->type = none;
	replaceCurrent(iff);
	} else if (iff->ifFalse->type == unreachable) {
	assert(isConcreteWasmType(iff->ifTrue->type));
	curr->value = iff->ifTrue;
	iff->ifTrue = curr;
	iff->type = none;
	replaceCurrent(iff);
	}
	}
	}

	void visitFunction(Function* curr) {
	auto* optimized = optimize(curr->body, curr->result != none);
	if (optimized) {
	curr->body = optimized;
	} else {
	ExpressionManipulator::nop(curr->body);
	}
	if (curr->result == none && !EffectAnalyzer(getPassOptions(), curr->body).hasSideEffects()) {
	ExpressionManipulator::nop(curr->body);
	}
	}
	};

	Pass *createVacuumPass() {
	return new Vacuum();
	}

	} // namespace wasm