RandomizeRegisterInit.cpp

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//===- RandomizeRegisterInit.cpp - Randomize register initialization ------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the RandomizeRegisterInit pass.
//
//===----------------------------------------------------------------------===//
 
#include "circt/Dialect/FIRRTL/FIRRTLAnnotations.h"
#include "circt/Dialect/FIRRTL/FIRRTLOps.h"
#include "circt/Dialect/FIRRTL/FIRRTLTypes.h"
#include "circt/Dialect/FIRRTL/Passes.h"
#include "mlir/IR/Attributes.h"
#include "mlir/IR/Builders.h"
#include "mlir/Pass/Pass.h"
 
namespace circt {
namespace firrtl {
#define GEN_PASS_DEF_RANDOMIZEREGISTERINIT
#include "circt/Dialect/FIRRTL/Passes.h.inc"
} // namespace firrtl
} // namespace circt
 
using namespace mlir;
using namespace circt;
using namespace firrtl;
 
namespace {
struct RandomizeRegisterInitPass
    : public circt::firrtl::impl::RandomizeRegisterInitBase<
          RandomizeRegisterInitPass> {
  void runOnOperation() override;
};
 
} // end anonymous namespace
 
/// Create attributes indicating the required size of random initialization
/// values for each register in the module, and mark which range of these values
/// each register should consume. The goal is for registers to always read the
/// same random bits for the same seed, regardless of optimizations that might
/// remove registers.
static void createRandomizationAttributes(FModuleOp mod) {
  OpBuilder builder(mod);
 
  // Walk all registers.
  uint64_t currentWidth = 0;
  auto ui64Type = builder.getIntegerType(64, false);
  mod.walk([&](Operation *op) {
    if (!isa<RegOp, RegResetOp>(op))
      return;
 
    // Compute the width of all registers, and remember which bits are assigned
    // to each register.
    auto regType = type_cast<FIRRTLBaseType>(op->getResult(0).getType());
    std::optional<int64_t> regWidth = getBitWidth(regType);
    assert(regWidth.has_value() && "register must have a valid FIRRTL width");
 
    auto start = builder.getIntegerAttr(ui64Type, currentWidth);
    op->setAttr("firrtl.random_init_start", start);
 
    currentWidth += *regWidth;
  });
}
 
void RandomizeRegisterInitPass::runOnOperation() {
  createRandomizationAttributes(getOperation());
}