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//===-- LLVMInsertChainFolder.cpp -----------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "flang/Optimizer/CodeGen/LLVMInsertChainFolder.h"
#include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/IR/Builders.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "flang-insert-folder"
#include <deque>
namespace {
// Helper class to construct the attribute elements of an aggregate value being
// folded without creating a full mlir::Attribute representation for each step
// of the insert value chain, which would both be expensive in terms of
// compilation time and memory (since the intermediate Attribute would survive,
// unused, inside the mlir context).
class InsertChainBackwardFolder {
// Type for the current value of an element of the aggregate value being
// constructed by the insert chain.
// At any point of the insert chain, the value of an element is either:
// - nullptr: not yet known, the insert has not yet been seen.
// - an mlir::Attribute: the element is fully defined.
// - a nested InsertChainBackwardFolder: the element is itself an aggregate
// and its sub-elements have been partially defined (insert with mutliple
// indices have been seen).
// The insertion folder assumes backward walk of the insert chain. Once an
// element or sub-element has been defined, it is not overriden by new
// insertions (last insert wins).
using InFlightValue =
llvm::PointerUnion<mlir::Attribute, InsertChainBackwardFolder *>;
public:
InsertChainBackwardFolder(
mlir::Type type, std::deque<InsertChainBackwardFolder> *folderStorage)
: values(getNumElements(type), mlir::Attribute{}),
folderStorage{folderStorage}, type{type} {}
/// Push
bool pushValue(mlir::Attribute val, llvm::ArrayRef<int64_t> at);
mlir::Attribute finalize(mlir::Attribute defaultFieldValue);
private:
static int64_t getNumElements(mlir::Type type) {
if (auto structTy =
llvm::dyn_cast_if_present<mlir::LLVM::LLVMStructType>(type))
return structTy.getBody().size();
if (auto arrayTy =
llvm::dyn_cast_if_present<mlir::LLVM::LLVMArrayType>(type))
return arrayTy.getNumElements();
return 0;
}
static mlir::Type getSubElementType(mlir::Type type, int64_t field) {
if (auto arrayTy =
llvm::dyn_cast_if_present<mlir::LLVM::LLVMArrayType>(type))
return arrayTy.getElementType();
if (auto structTy =
llvm::dyn_cast_if_present<mlir::LLVM::LLVMStructType>(type))
return structTy.getBody()[field];
return nullptr;
}
// Current element value of the aggregate value being built.
llvm::SmallVector<InFlightValue> values;
// std::deque is used to allocate storage for nested list and guarantee the
// stability of the InsertChainBackwardFolder* used as element value.
std::deque<InsertChainBackwardFolder> *folderStorage;
// Type of the aggregate value being built.
mlir::Type type;
};
} // namespace
// Helper to fold the value being inserted by an llvm.insert_value.
// This may call tryFoldingLLVMInsertChain if the value is an aggregate and
// was itself constructed by a different insert chain.
// Returns a nullptr Attribute if the value could not be folded.
static mlir::Attribute getAttrIfConstant(mlir::Value val,
mlir::OpBuilder &rewriter) {
if (auto cst = val.getDefiningOp<mlir::LLVM::ConstantOp>())
return cst.getValue();
if (auto insert = val.getDefiningOp<mlir::LLVM::InsertValueOp>()) {
llvm::FailureOr<mlir::Attribute> attr =
fir::tryFoldingLLVMInsertChain(val, rewriter);
if (succeeded(attr))
return *attr;
return nullptr;
}
if (val.getDefiningOp<mlir::LLVM::ZeroOp>())
return mlir::LLVM::ZeroAttr::get(val.getContext());
if (val.getDefiningOp<mlir::LLVM::UndefOp>())
return mlir::LLVM::UndefAttr::get(val.getContext());
if (mlir::Operation *op = val.getDefiningOp()) {
unsigned resNum = llvm::cast<mlir::OpResult>(val).getResultNumber();
llvm::SmallVector<mlir::Value> results;
if (mlir::succeeded(rewriter.tryFold(op, results)) &&
results.size() > resNum) {
if (auto cst = results[resNum].getDefiningOp<mlir::LLVM::ConstantOp>())
return cst.getValue();
}
}
if (auto trunc = val.getDefiningOp<mlir::LLVM::TruncOp>())
if (auto attr = getAttrIfConstant(trunc.getArg(), rewriter))
if (auto intAttr = llvm::dyn_cast<mlir::IntegerAttr>(attr))
return mlir::IntegerAttr::get(trunc.getType(), intAttr.getInt());
LLVM_DEBUG(llvm::dbgs() << "cannot fold insert value operand: " << val
<< "\n");
return nullptr;
}
mlir::Attribute
InsertChainBackwardFolder::finalize(mlir::Attribute defaultFieldValue) {
llvm::SmallVector<mlir::Attribute> attrs = llvm::map_to_vector(
values, [&](InFlightValue inFlight) -> mlir::Attribute {
if (!inFlight)
return defaultFieldValue;
if (auto attr = llvm::dyn_cast<mlir::Attribute>(inFlight))
return attr;
return llvm::cast<InsertChainBackwardFolder *>(inFlight)->finalize(
defaultFieldValue);
});
return mlir::ArrayAttr::get(type.getContext(), attrs);
}
bool InsertChainBackwardFolder::pushValue(mlir::Attribute val,
llvm::ArrayRef<int64_t> at) {
if (at.size() == 0 || at[0] >= static_cast<int64_t>(values.size()))
return false;
InFlightValue &inFlight = values[at[0]];
if (!inFlight) {
if (at.size() == 1) {
inFlight = val;
return true;
}
// This is the first insert to a nested field. Create a
// InsertChainBackwardFolder for the current element value.
mlir::Type subType = getSubElementType(type, at[0]);
if (!subType)
return false;
InsertChainBackwardFolder &inFlightList =
folderStorage->emplace_back(subType, folderStorage);
inFlight = &inFlightList;
return inFlightList.pushValue(val, at.drop_front());
}
// Keep last inserted value if already set.
if (llvm::isa<mlir::Attribute>(inFlight))
return true;
auto *inFlightList = llvm::cast<InsertChainBackwardFolder *>(inFlight);
if (at.size() == 1) {
if (!llvm::isa<mlir::LLVM::ZeroAttr, mlir::LLVM::UndefAttr>(val)) {
LLVM_DEBUG(llvm::dbgs()
<< "insert chain sub-element partially overwritten initial "
"value is not zero or undef\n");
return false;
}
inFlight = inFlightList->finalize(val);
return true;
}
return inFlightList->pushValue(val, at.drop_front());
}
llvm::FailureOr<mlir::Attribute>
fir::tryFoldingLLVMInsertChain(mlir::Value val, mlir::OpBuilder &rewriter) {
if (auto cst = val.getDefiningOp<mlir::LLVM::ConstantOp>())
return cst.getValue();
if (auto insert = val.getDefiningOp<mlir::LLVM::InsertValueOp>()) {
LLVM_DEBUG(llvm::dbgs() << "trying to fold insert chain:" << val << "\n");
if (auto structTy =
llvm::dyn_cast<mlir::LLVM::LLVMStructType>(insert.getType())) {
mlir::LLVM::InsertValueOp currentInsert = insert;
mlir::LLVM::InsertValueOp lastInsert;
std::deque<InsertChainBackwardFolder> folderStorage;
InsertChainBackwardFolder inFlightList(structTy, &folderStorage);
while (currentInsert) {
mlir::Attribute attr =
getAttrIfConstant(currentInsert.getValue(), rewriter);
if (!attr)
return llvm::failure();
if (!inFlightList.pushValue(attr, currentInsert.getPosition()))
return llvm::failure();
lastInsert = currentInsert;
currentInsert = currentInsert.getContainer()
.getDefiningOp<mlir::LLVM::InsertValueOp>();
}
mlir::Attribute defaultVal;
if (lastInsert) {
if (lastInsert.getContainer().getDefiningOp<mlir::LLVM::ZeroOp>())
defaultVal = mlir::LLVM::ZeroAttr::get(val.getContext());
else if (lastInsert.getContainer().getDefiningOp<mlir::LLVM::UndefOp>())
defaultVal = mlir::LLVM::UndefAttr::get(val.getContext());
}
if (!defaultVal) {
LLVM_DEBUG(llvm::dbgs()
<< "insert chain initial value is not Zero or Undef\n");
return llvm::failure();
}
return inFlightList.finalize(defaultVal);
}
}
return llvm::failure();
}
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