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/*
* Copyright 2022 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.
*/
//
// Lowers sign-ext operations into wasm MVP operations.
//
#include "pass.h"
#include "wasm-builder.h"
#include "wasm.h"
namespace wasm {
struct SignExtLowering : public WalkerPass<PostWalker<SignExtLowering>> {
template<typename T>
void lowerToShifts(Expression* value,
BinaryOp leftShift,
BinaryOp rightShift,
T originalBits) {
// To sign-extend, we shift all the way left so the effective sign bit is
// where the actual sign bit is. For example, when sign-extending i8, the
// effective sign bit is at bit 8, and we shift it to the actual place of
// the sign bit, which is 32 for i32 or 64 for i64. Then we do a signed
// shift in the other direction, which fills with the proper bit all the
// way back, so e.g.
//
// 0x000000ff =(shift left)=> 0xff000000 =(shift right)=> 0xffffffff
//
T shiftBits = (sizeof(T) * 8) - originalBits;
Builder builder(*getModule());
replaceCurrent(builder.makeBinary(
rightShift,
builder.makeBinary(leftShift, value, builder.makeConst(shiftBits)),
builder.makeConst(shiftBits)));
}
void visitUnary(Unary* curr) {
switch (curr->op) {
case ExtendS8Int32:
lowerToShifts(curr->value, ShlInt32, ShrSInt32, int32_t(8));
break;
case ExtendS16Int32:
lowerToShifts(curr->value, ShlInt32, ShrSInt32, int32_t(16));
break;
case ExtendS8Int64:
lowerToShifts(curr->value, ShlInt64, ShrSInt64, int64_t(8));
break;
case ExtendS16Int64:
lowerToShifts(curr->value, ShlInt64, ShrSInt64, int64_t(16));
break;
case ExtendS32Int64:
lowerToShifts(curr->value, ShlInt64, ShrSInt64, int64_t(32));
break;
default: {
}
}
}
void run(Module* module) override {
if (!module->features.has(FeatureSet::SignExt)) {
return;
}
Super::run(module);
module->features.disable(FeatureSet::SignExt);
}
};
Pass* createSignExtLoweringPass() { return new SignExtLowering(); }
} // namespace wasm
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