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/*
* Copyright 2017 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.
*/
#ifndef wasm_ir_memory_h
#define wasm_ir_memory_h
#include <algorithm>
#include <vector>
#include "literal.h"
#include "wasm-binary.h"
#include "wasm-builder.h"
#include "wasm-limits.h"
#include "wasm.h"
namespace wasm::MemoryUtils {
// Flattens memory into a single data segment, or no segment. If there is
// a segment, it starts at 0.
// Returns true if successful (e.g. relocatable segments cannot be flattened).
// Does not yet support multimemory
bool flatten(Module& wasm);
// Ensures that a memory exists (of minimal size).
inline void ensureExists(Module* wasm) {
if (wasm->memories.empty()) {
auto memory = Builder::makeMemory("0");
memory->initial = memory->max = 1;
wasm->addMemory(std::move(memory));
}
}
// Try to merge segments until they fit into web limitations.
// Return true if successful.
// Does not yet support multimemory
inline bool ensureLimitedSegments(Module& module) {
if (module.memories.size() > 1) {
return false;
}
auto& dataSegments = module.dataSegments;
if (dataSegments.size() <= WebLimitations::MaxDataSegments) {
return true;
}
// Conservatively refuse to change segments if there might be memory.init
// and data.drop instructions.
if (module.features.hasBulkMemory()) {
return false;
}
auto isEmpty = [](DataSegment& segment) { return segment.data.size() == 0; };
auto isConstantOffset = [](DataSegment& segment) {
return segment.offset && segment.offset->is<Const>();
};
Index numConstant = 0, numDynamic = 0;
bool hasPassiveSegments = false;
for (auto& segment : dataSegments) {
if (!isEmpty(*segment)) {
if (isConstantOffset(*segment)) {
numConstant++;
} else {
numDynamic++;
}
}
hasPassiveSegments |= segment->isPassive;
}
if (hasPassiveSegments) {
return false;
}
// check if we have too many dynamic data segments, which we can do nothing
// about
if (numDynamic + 1 >= WebLimitations::MaxDataSegments) {
return false;
}
// we'll merge constant segments if we must
if (numConstant + numDynamic >= WebLimitations::MaxDataSegments) {
numConstant = WebLimitations::MaxDataSegments - numDynamic - 1;
[[maybe_unused]] auto num = numConstant + numDynamic;
assert(num == WebLimitations::MaxDataSegments - 1);
}
std::vector<std::unique_ptr<wasm::DataSegment>> mergedSegments;
mergedSegments.reserve(WebLimitations::MaxDataSegments);
// drop empty segments and pass through dynamic-offset segments
for (auto& segment : dataSegments) {
if (isEmpty(*segment)) {
continue;
}
if (isConstantOffset(*segment)) {
continue;
}
mergedSegments.push_back(std::move(segment));
}
// from here on, we concern ourselves with non-empty constant-offset
// segments, the ones which we may need to merge
auto isRelevant = [&](DataSegment& segment) {
return !isEmpty(segment) && isConstantOffset(segment);
};
for (Index i = 0; i < dataSegments.size(); i++) {
auto& segment = dataSegments[i];
if (!isRelevant(*segment)) {
continue;
}
if (mergedSegments.size() + 2 < WebLimitations::MaxDataSegments) {
mergedSegments.push_back(std::move(segment));
continue;
}
// we can emit only one more segment! merge everything into one
// start the combined segment at the bottom of them all
auto start = segment->offset->cast<Const>()->value.getInteger();
for (Index j = i + 1; j < dataSegments.size(); j++) {
auto& segment = dataSegments[j];
if (!isRelevant(*segment)) {
continue;
}
auto offset = segment->offset->cast<Const>()->value.getInteger();
start = std::min(start, offset);
}
// create the segment and add in all the data
auto* c = module.allocator.alloc<Const>();
c->value = Literal(int32_t(start));
c->type = Type::i32;
auto combined = Builder::makeDataSegment();
combined->memory = module.memories[0]->name;
combined->offset = c;
for (Index j = i; j < dataSegments.size(); j++) {
auto& segment = dataSegments[j];
if (!isRelevant(*segment)) {
continue;
}
auto offset = segment->offset->cast<Const>()->value.getInteger();
auto needed = offset + segment->data.size() - start;
if (combined->data.size() < needed) {
combined->data.resize(needed);
}
std::copy(segment->data.begin(),
segment->data.end(),
combined->data.begin() + (offset - start));
}
mergedSegments.push_back(std::move(combined));
break;
}
dataSegments.swap(mergedSegments);
module.updateDataSegmentsMap();
return true;
}
} // namespace wasm::MemoryUtils
#endif // wasm_ir_memory_h
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