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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.h"
#include "wasm-binary.h"
namespace wasm {
namespace MemoryUtils {
// flattens memory into a single data segment. returns true if successful
inline bool flatten(Memory& memory) {
if (memory.segments.size() == 0) return true;
std::vector<char> data;
for (auto& segment : memory.segments) {
if (segment.isPassive) {
return false;
}
auto* offset = segment.offset->dynCast<Const>();
if (!offset) return false;
}
for (auto& segment : memory.segments) {
auto* offset = segment.offset->dynCast<Const>();
Index start = offset->value.getInteger();
Index end = start + segment.data.size();
if (end > data.size()) {
data.resize(end);
}
std::copy(segment.data.begin(), segment.data.end(), data.begin() + start);
}
memory.segments.resize(1);
memory.segments[0].offset->cast<Const>()->value = Literal(int32_t(0));
memory.segments[0].data.swap(data);
return true;
}
// Ensures that the memory exists (of minimal size).
inline void ensureExists(Memory& memory) {
if (!memory.exists) {
memory.exists = true;
memory.initial = memory.max = 1;
}
}
// Try to merge segments until they fit into web limitations.
// Return true if successful.
inline bool ensureLimitedSegments(Module& module) {
Memory& memory = module.memory;
if (memory.segments.size() <= WebLimitations::MaxDataSegments) {
return true;
}
auto isEmpty = [](Memory::Segment& segment) {
return segment.data.size() == 0;
};
auto isConstantOffset = [](Memory::Segment& segment) {
return segment.offset && segment.offset->is<Const>();
};
Index numConstant = 0,
numDynamic = 0;
bool hasPassiveSegments = false;
for (auto& segment : memory.segments) {
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
auto num = numConstant + numDynamic;
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;
num = numConstant + numDynamic;
assert(num == WebLimitations::MaxDataSegments - 1);
}
std::vector<Memory::Segment> mergedSegments;
mergedSegments.reserve(WebLimitations::MaxDataSegments);
// drop empty segments and pass through dynamic-offset segments
for (auto& segment : memory.segments) {
if (isEmpty(segment)) continue;
if (isConstantOffset(segment)) continue;
mergedSegments.push_back(segment);
}
// from here on, we concern ourselves with non-empty constant-offset
// segments, the ones which we may need to merge
auto isRelevant = [&](Memory::Segment& segment) {
return !isEmpty(segment) && isConstantOffset(segment);
};
for (Index i = 0; i < memory.segments.size(); i++) {
auto& segment = memory.segments[i];
if (!isRelevant(segment)) continue;
if (mergedSegments.size() + 2 < WebLimitations::MaxDataSegments) {
mergedSegments.push_back(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 < memory.segments.size(); j++) {
auto& segment = memory.segments[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 = i32;
Memory::Segment combined(c);
for (Index j = i; j < memory.segments.size(); j++) {
auto& segment = memory.segments[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(combined);
break;
}
memory.segments.swap(mergedSegments);
return true;
}
} // namespace MemoryUtils
} // namespace wasm
#endif // wasm_ir_memory_h
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