ee407e17a3
This PR is an implementation for changes proposed in https://discourse.llvm.org/t/rfc-distinguish-between-data-and-non-data-in-fir-alias-analysis/78759 Test updates were made when the query was on the wrong reference. So, it is my hope that this will clear ambiguity on the nature of the queries from here on. There are also some TODOs that were addressed. It also partly implements what https://github.com/llvm/llvm-project/pull/87723 is attempting to accomplish. At least, on a point-to-point query between references, the distinction is made. To apply it to TBAA, would be another PR. Note that, the changes were minimal in the TBAA code to retain the current results.
391 lines
14 KiB
C++
391 lines
14 KiB
C++
//===- AliasAnalysis.cpp - Alias Analysis for FIR ------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "flang/Optimizer/Analysis/AliasAnalysis.h"
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#include "flang/Optimizer/Dialect/FIROps.h"
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#include "flang/Optimizer/Dialect/FIROpsSupport.h"
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#include "flang/Optimizer/Dialect/FIRType.h"
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#include "flang/Optimizer/Dialect/FortranVariableInterface.h"
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#include "flang/Optimizer/HLFIR/HLFIROps.h"
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#include "mlir/Analysis/AliasAnalysis.h"
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#include "mlir/IR/BuiltinOps.h"
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#include "mlir/IR/Value.h"
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#include "mlir/Interfaces/SideEffectInterfaces.h"
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#include "llvm/ADT/TypeSwitch.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Debug.h"
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using namespace mlir;
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#define DEBUG_TYPE "fir-alias-analysis"
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//===----------------------------------------------------------------------===//
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// AliasAnalysis: alias
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//===----------------------------------------------------------------------===//
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static bool isDummyArgument(mlir::Value v) {
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auto blockArg{mlir::dyn_cast<mlir::BlockArgument>(v)};
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if (!blockArg)
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return false;
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auto *owner{blockArg.getOwner()};
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return owner->isEntryBlock() &&
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mlir::isa<mlir::FunctionOpInterface>(owner->getParentOp());
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}
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/// Temporary function to skip through all the no op operations
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/// TODO: Generalize support of fir.load
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static mlir::Value getOriginalDef(mlir::Value v) {
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mlir::Operation *defOp;
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bool breakFromLoop = false;
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while (!breakFromLoop && (defOp = v.getDefiningOp())) {
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llvm::TypeSwitch<Operation *>(defOp)
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.Case<fir::ConvertOp>([&](fir::ConvertOp op) { v = op.getValue(); })
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.Case<fir::DeclareOp, hlfir::DeclareOp>(
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[&](auto op) { v = op.getMemref(); })
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.Default([&](auto op) { breakFromLoop = true; });
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}
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return v;
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}
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namespace fir {
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void AliasAnalysis::Source::print(llvm::raw_ostream &os) const {
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if (auto v = llvm::dyn_cast<mlir::Value>(origin.u))
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os << v;
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else if (auto gbl = llvm::dyn_cast<mlir::SymbolRefAttr>(origin.u))
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os << gbl;
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os << " SourceKind: " << EnumToString(kind);
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os << " Type: " << valueType << " ";
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if (origin.isData) {
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os << " following data ";
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} else {
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os << " following box reference ";
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}
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attributes.Dump(os, EnumToString);
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}
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bool AliasAnalysis::Source::isPointerReference(mlir::Type ty) {
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auto eleTy = fir::dyn_cast_ptrEleTy(ty);
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if (!eleTy)
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return false;
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return fir::isPointerType(eleTy) || mlir::isa<fir::PointerType>(eleTy);
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}
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bool AliasAnalysis::Source::isTargetOrPointer() const {
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return attributes.test(Attribute::Pointer) ||
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attributes.test(Attribute::Target);
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}
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bool AliasAnalysis::Source::isDummyArgument() const {
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if (auto v = origin.u.dyn_cast<mlir::Value>()) {
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return ::isDummyArgument(v);
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}
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return false;
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}
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bool AliasAnalysis::Source::isData() const { return origin.isData; }
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bool AliasAnalysis::Source::isBoxData() const {
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return mlir::isa<fir::BaseBoxType>(fir::unwrapRefType(valueType)) &&
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origin.isData;
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}
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bool AliasAnalysis::Source::isRecordWithPointerComponent() const {
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auto eleTy = fir::dyn_cast_ptrEleTy(valueType);
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if (!eleTy)
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return false;
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// TO DO: Look for pointer components
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return mlir::isa<fir::RecordType>(eleTy);
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}
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AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
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auto lhsSrc = getSource(lhs);
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auto rhsSrc = getSource(rhs);
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bool approximateSource = lhsSrc.approximateSource || rhsSrc.approximateSource;
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LLVM_DEBUG(llvm::dbgs() << "\nAliasAnalysis::alias\n";
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llvm::dbgs() << " lhs: " << lhs << "\n";
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llvm::dbgs() << " lhsSrc: " << lhsSrc << "\n";
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llvm::dbgs() << " rhs: " << rhs << "\n";
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llvm::dbgs() << " rhsSrc: " << rhsSrc << "\n";);
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// Indirect case currently not handled. Conservatively assume
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// it aliases with everything
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if (lhsSrc.kind >= SourceKind::Indirect ||
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rhsSrc.kind >= SourceKind::Indirect) {
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return AliasResult::MayAlias;
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}
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if (lhsSrc.kind == rhsSrc.kind) {
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if (lhsSrc.origin == rhsSrc.origin) {
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LLVM_DEBUG(llvm::dbgs()
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<< " aliasing because same source kind and origin\n");
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if (approximateSource)
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return AliasResult::MayAlias;
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return AliasResult::MustAlias;
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}
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// Two host associated accesses may overlap due to an equivalence.
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if (lhsSrc.kind == SourceKind::HostAssoc) {
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LLVM_DEBUG(llvm::dbgs() << " aliasing because of host association\n");
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return AliasResult::MayAlias;
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}
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}
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Source *src1, *src2;
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if (lhsSrc.kind < rhsSrc.kind) {
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src1 = &lhsSrc;
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src2 = &rhsSrc;
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} else {
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src1 = &rhsSrc;
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src2 = &lhsSrc;
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}
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if (src1->kind == SourceKind::Argument &&
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src2->kind == SourceKind::HostAssoc) {
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// Treat the host entity as TARGET for the purpose of disambiguating
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// it with a dummy access. It is required for this particular case:
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// subroutine test
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// integer :: x(10)
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// call inner(x)
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// contains
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// subroutine inner(y)
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// integer, target :: y(:)
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// x(1) = y(1)
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// end subroutine inner
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// end subroutine test
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//
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// F18 15.5.2.13 (4) (b) allows 'x' and 'y' to address the same object.
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// 'y' has an explicit TARGET attribute, but 'x' has neither TARGET
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// nor POINTER.
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src2->attributes.set(Attribute::Target);
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}
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// Dummy TARGET/POINTER argument may alias with a global TARGET/POINTER.
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if (src1->isTargetOrPointer() && src2->isTargetOrPointer() &&
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src1->isData() == src2->isData()) {
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LLVM_DEBUG(llvm::dbgs() << " aliasing because of target or pointer\n");
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return AliasResult::MayAlias;
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}
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// Box for POINTER component inside an object of a derived type
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// may alias box of a POINTER object, as well as boxes for POINTER
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// components inside two objects of derived types may alias.
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if ((src1->isRecordWithPointerComponent() && src2->isTargetOrPointer()) ||
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(src2->isRecordWithPointerComponent() && src1->isTargetOrPointer()) ||
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(src1->isRecordWithPointerComponent() &&
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src2->isRecordWithPointerComponent())) {
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LLVM_DEBUG(llvm::dbgs() << " aliasing because of pointer components\n");
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return AliasResult::MayAlias;
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}
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return AliasResult::NoAlias;
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}
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//===----------------------------------------------------------------------===//
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// AliasAnalysis: getModRef
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//===----------------------------------------------------------------------===//
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/// This is mostly inspired by MLIR::LocalAliasAnalysis with 2 notable
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/// differences 1) Regions are not handled here but will be handled by a data
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/// flow analysis to come 2) Allocate and Free effects are considered
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/// modifying
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ModRefResult AliasAnalysis::getModRef(Operation *op, Value location) {
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MemoryEffectOpInterface interface = dyn_cast<MemoryEffectOpInterface>(op);
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if (!interface)
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return ModRefResult::getModAndRef();
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// Build a ModRefResult by merging the behavior of the effects of this
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// operation.
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SmallVector<MemoryEffects::EffectInstance> effects;
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interface.getEffects(effects);
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ModRefResult result = ModRefResult::getNoModRef();
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for (const MemoryEffects::EffectInstance &effect : effects) {
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// Check for an alias between the effect and our memory location.
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AliasResult aliasResult = AliasResult::MayAlias;
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if (Value effectValue = effect.getValue())
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aliasResult = alias(effectValue, location);
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// If we don't alias, ignore this effect.
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if (aliasResult.isNo())
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continue;
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// Merge in the corresponding mod or ref for this effect.
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if (isa<MemoryEffects::Read>(effect.getEffect()))
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result = result.merge(ModRefResult::getRef());
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else
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result = result.merge(ModRefResult::getMod());
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if (result.isModAndRef())
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break;
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}
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return result;
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}
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AliasAnalysis::Source::Attributes
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getAttrsFromVariable(fir::FortranVariableOpInterface var) {
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AliasAnalysis::Source::Attributes attrs;
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if (var.isTarget())
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attrs.set(AliasAnalysis::Attribute::Target);
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if (var.isPointer())
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attrs.set(AliasAnalysis::Attribute::Pointer);
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if (var.isIntentIn())
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attrs.set(AliasAnalysis::Attribute::IntentIn);
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return attrs;
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}
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AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v) {
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auto *defOp = v.getDefiningOp();
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SourceKind type{SourceKind::Unknown};
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mlir::Type ty;
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bool breakFromLoop{false};
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bool approximateSource{false};
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bool followBoxData{mlir::isa<fir::BaseBoxType>(v.getType())};
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bool isBoxRef{fir::isa_ref_type(v.getType()) &&
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mlir::isa<fir::BaseBoxType>(fir::unwrapRefType(v.getType()))};
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bool followingData = !isBoxRef;
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mlir::SymbolRefAttr global;
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Source::Attributes attributes;
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while (defOp && !breakFromLoop) {
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ty = defOp->getResultTypes()[0];
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llvm::TypeSwitch<Operation *>(defOp)
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.Case<fir::AllocaOp, fir::AllocMemOp>([&](auto op) {
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// Unique memory allocation.
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type = SourceKind::Allocate;
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breakFromLoop = true;
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})
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.Case<fir::ConvertOp>([&](auto op) {
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// Skip ConvertOp's and track further through the operand.
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v = op->getOperand(0);
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defOp = v.getDefiningOp();
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})
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.Case<fir::BoxAddrOp>([&](auto op) {
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v = op->getOperand(0);
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defOp = v.getDefiningOp();
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if (mlir::isa<fir::BaseBoxType>(v.getType()))
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followBoxData = true;
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})
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.Case<fir::ArrayCoorOp, fir::CoordinateOp>([&](auto op) {
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v = op->getOperand(0);
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defOp = v.getDefiningOp();
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if (mlir::isa<fir::BaseBoxType>(v.getType()))
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followBoxData = true;
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approximateSource = true;
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})
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.Case<fir::EmboxOp, fir::ReboxOp>([&](auto op) {
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if (followBoxData) {
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v = op->getOperand(0);
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defOp = v.getDefiningOp();
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} else
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breakFromLoop = true;
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})
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.Case<fir::LoadOp>([&](auto op) {
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// If the load is from a leaf source, return the leaf. Do not track
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// through indirections otherwise.
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// TODO: Add support to fir.alloca and fir.allocmem
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auto def = getOriginalDef(op.getMemref());
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if (isDummyArgument(def) ||
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def.template getDefiningOp<fir::AddrOfOp>()) {
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v = def;
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defOp = v.getDefiningOp();
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return;
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}
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// No further tracking for addresses loaded from memory for now.
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type = SourceKind::Indirect;
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breakFromLoop = true;
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})
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.Case<fir::AddrOfOp>([&](auto op) {
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// Address of a global scope object.
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ty = v.getType();
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type = SourceKind::Global;
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auto globalOpName = mlir::OperationName(
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fir::GlobalOp::getOperationName(), defOp->getContext());
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if (fir::valueHasFirAttribute(
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v, fir::GlobalOp::getTargetAttrName(globalOpName)))
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attributes.set(Attribute::Target);
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// TODO: Take followBoxData into account when setting the pointer
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// attribute
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if (Source::isPointerReference(ty))
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attributes.set(Attribute::Pointer);
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global = llvm::cast<fir::AddrOfOp>(op).getSymbol();
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breakFromLoop = true;
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})
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.Case<hlfir::DeclareOp, fir::DeclareOp>([&](auto op) {
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auto varIf = llvm::cast<fir::FortranVariableOpInterface>(defOp);
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// While going through a declare operation collect
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// the variable attributes from it. Right now, some
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// of the attributes are duplicated, e.g. a TARGET dummy
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// argument has the target attribute both on its declare
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// operation and on the entry block argument.
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// In case of host associated use, the declare operation
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// is the only carrier of the variable attributes,
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// so we have to collect them here.
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attributes |= getAttrsFromVariable(varIf);
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if (varIf.isHostAssoc()) {
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// Do not track past such DeclareOp, because it does not
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// currently provide any useful information. The host associated
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// access will end up dereferencing the host association tuple,
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// so we may as well stop right now.
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v = defOp->getResult(0);
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// TODO: if the host associated variable is a dummy argument
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// of the host, I think, we can treat it as SourceKind::Argument
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// for the purpose of alias analysis inside the internal procedure.
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type = SourceKind::HostAssoc;
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breakFromLoop = true;
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return;
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}
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// TODO: Look for the fortran attributes present on the operation
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// Track further through the operand
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v = op.getMemref();
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defOp = v.getDefiningOp();
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})
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.Case<hlfir::DesignateOp>([&](auto op) {
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// Track further through the memory indexed into
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// => if the source arrays/structures don't alias then nor do the
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// results of hlfir.designate
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v = op.getMemref();
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defOp = v.getDefiningOp();
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// TODO: there will be some cases which provably don't alias if one
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// takes into account the component or indices, which are currently
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// ignored here - leading to false positives
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// because of this limitation, we need to make sure we never return
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// MustAlias after going through a designate operation
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approximateSource = true;
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if (mlir::isa<fir::BaseBoxType>(v.getType()))
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followBoxData = true;
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})
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.Default([&](auto op) {
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defOp = nullptr;
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breakFromLoop = true;
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});
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}
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if (!defOp && type == SourceKind::Unknown)
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// Check if the memory source is coming through a dummy argument.
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if (isDummyArgument(v)) {
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type = SourceKind::Argument;
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ty = v.getType();
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if (fir::valueHasFirAttribute(v, fir::getTargetAttrName()))
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attributes.set(Attribute::Target);
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if (Source::isPointerReference(ty))
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attributes.set(Attribute::Pointer);
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}
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if (type == SourceKind::Global) {
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return {{global, followingData}, type, ty, attributes, approximateSource};
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}
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return {{v, followingData}, type, ty, attributes, approximateSource};
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}
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} // namespace fir
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