flang/lib/Semantics/compute-offsets.cpp

   1 //===-- lib/Semantics/compute-offsets.cpp -----------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "compute-offsets.h"
  10 #include "flang/Evaluate/fold-designator.h"
  11 #include "flang/Evaluate/fold.h"
  12 #include "flang/Evaluate/shape.h"
  13 #include "flang/Evaluate/type.h"
  14 #include "flang/Runtime/descriptor.h"
  15 #include "flang/Semantics/scope.h"
  16 #include "flang/Semantics/semantics.h"
  17 #include "flang/Semantics/symbol.h"
  18 #include "flang/Semantics/tools.h"
  19 #include "flang/Semantics/type.h"
  20 #include <algorithm>
  21 #include <vector>
  22
  23 namespace Fortran::semantics {
  24
  25 class ComputeOffsetsHelper {
  26 public:
  27   ComputeOffsetsHelper(SemanticsContext &context) : context_{context} {}
  28   void Compute(Scope &);
  29
  30 private:
  31   struct SizeAndAlignment {
  32     SizeAndAlignment() {}
  33     SizeAndAlignment(std::size_t bytes) : size{bytes}, alignment{bytes} {}
  34     SizeAndAlignment(std::size_t bytes, std::size_t align)
  35         : size{bytes}, alignment{align} {}
  36     std::size_t size{0};
  37     std::size_t alignment{0};
  38   };
  39   struct SymbolAndOffset {
  40     SymbolAndOffset(Symbol &s, std::size_t off, const EquivalenceObject &obj)
  41         : symbol{s}, offset{off}, object{&obj} {}
  42     SymbolAndOffset(const SymbolAndOffset &) = default;
  43     MutableSymbolRef symbol;
  44     std::size_t offset;
  45     const EquivalenceObject *object;
  46   };
  47
  48   void DoCommonBlock(Symbol &);
  49   void DoEquivalenceBlockBase(Symbol &, SizeAndAlignment &);
  50   void DoEquivalenceSet(const EquivalenceSet &);
  51   SymbolAndOffset Resolve(const SymbolAndOffset &);
  52   std::size_t ComputeOffset(const EquivalenceObject &);
  53   // Returns amount of padding that was needed for alignment
  54   std::size_t DoSymbol(Symbol &);
  55   SizeAndAlignment GetSizeAndAlignment(const Symbol &, bool entire);
  56   std::size_t Align(std::size_t, std::size_t);
  57
  58   SemanticsContext &context_;
  59   std::size_t offset_{0};
  60   std::size_t alignment_{1};
  61   // symbol -> symbol+offset that determines its location, from EQUIVALENCE
  62   std::map<MutableSymbolRef, SymbolAndOffset, SymbolAddressCompare> dependents_;
  63   // base symbol -> SizeAndAlignment for each distinct EQUIVALENCE block
  64   std::map<MutableSymbolRef, SizeAndAlignment, SymbolAddressCompare>
  65       equivalenceBlock_;
  66 };
  67
  68 void ComputeOffsetsHelper::Compute(Scope &scope) {
  69   for (Scope &child : scope.children()) {
  70     ComputeOffsets(context_, child);
  71   }
  72   if (scope.symbol() && scope.IsDerivedTypeWithKindParameter()) {
  73     return; // only process instantiations of kind parameterized derived types
  74   }
  75   if (scope.alignment().has_value()) {
  76     return; // prevent infinite recursion in error cases
  77   }
  78   scope.SetAlignment(0);
  79   // Build dependents_ from equivalences: symbol -> symbol+offset
  80   for (const EquivalenceSet &set : scope.equivalenceSets()) {
  81     DoEquivalenceSet(set);
  82   }
  83   // Compute a base symbol and overall block size for each
  84   // disjoint EQUIVALENCE storage sequence.
  85   for (auto &[symbol, dep] : dependents_) {
  86     dep = Resolve(dep);
  87     CHECK(symbol->size() == 0);
  88     auto symInfo{GetSizeAndAlignment(*symbol, true)};
  89     symbol->set_size(symInfo.size);
  90     Symbol &base{*dep.symbol};
  91     auto iter{equivalenceBlock_.find(base)};
  92     std::size_t minBlockSize{dep.offset + symInfo.size};
  93     if (iter == equivalenceBlock_.end()) {
  94       equivalenceBlock_.emplace(
  95           base, SizeAndAlignment{minBlockSize, symInfo.alignment});
  96     } else {
  97       SizeAndAlignment &blockInfo{iter->second};
  98       blockInfo.size = std::max(blockInfo.size, minBlockSize);
  99       blockInfo.alignment = std::max(blockInfo.alignment, symInfo.alignment);
 100     }
 101   }
 102   // Assign offsets for non-COMMON EQUIVALENCE blocks
 103   for (auto &[symbol, blockInfo] : equivalenceBlock_) {
 104     if (!FindCommonBlockContaining(*symbol)) {
 105       DoSymbol(*symbol);
 106       DoEquivalenceBlockBase(*symbol, blockInfo);
 107       offset_ = std::max(offset_, symbol->offset() + blockInfo.size);
 108     }
 109   }
 110   // Process remaining non-COMMON symbols; this is all of them if there
 111   // was no use of EQUIVALENCE in the scope.
 112   for (auto &symbol : scope.GetSymbols()) {
 113     if (!FindCommonBlockContaining(*symbol) &&
 114         dependents_.find(symbol) == dependents_.end() &&
 115         equivalenceBlock_.find(symbol) == equivalenceBlock_.end()) {
 116       DoSymbol(*symbol);
 117     }
 118   }
 119   scope.set_size(offset_);
 120   scope.SetAlignment(alignment_);
 121   // Assign offsets in COMMON blocks, unless this scope is a BLOCK construct,
 122   // where COMMON blocks are illegal (C1107 and C1108).
 123   if (scope.kind() != Scope::Kind::BlockConstruct) {
 124     for (auto &pair : scope.commonBlocks()) {
 125       DoCommonBlock(*pair.second);
 126     }
 127   }
 128   for (auto &[symbol, dep] : dependents_) {
 129     symbol->set_offset(dep.symbol->offset() + dep.offset);
 130     if (const auto *block{FindCommonBlockContaining(*dep.symbol)}) {
 131       symbol->get<ObjectEntityDetails>().set_commonBlock(*block);
 132     }
 133   }
 134 }
 135
 136 auto ComputeOffsetsHelper::Resolve(const SymbolAndOffset &dep)
 137     -> SymbolAndOffset {
 138   auto it{dependents_.find(*dep.symbol)};
 139   if (it == dependents_.end()) {
 140     return dep;
 141   } else {
 142     SymbolAndOffset result{Resolve(it->second)};
 143     result.offset += dep.offset;
 144     result.object = dep.object;
 145     return result;
 146   }
 147 }
 148
 149 void ComputeOffsetsHelper::DoCommonBlock(Symbol &commonBlock) {
 150   auto &details{commonBlock.get<CommonBlockDetails>()};
 151   offset_ = 0;
 152   alignment_ = 0;
 153   std::size_t minSize{0};
 154   std::size_t minAlignment{0};
 155   for (auto &object : details.objects()) {
 156     Symbol &symbol{*object};
 157     auto errorSite{
 158         commonBlock.name().empty() ? symbol.name() : commonBlock.name()};
 159     if (std::size_t padding{DoSymbol(symbol.GetUltimate())}) {
 160       context_.Say(errorSite,
 161           "COMMON block /%s/ requires %zd bytes of padding before '%s' for alignment"_port_en_US,
 162           commonBlock.name(), padding, symbol.name());
 163     }
 164     auto eqIter{equivalenceBlock_.end()};
 165     auto iter{dependents_.find(symbol)};
 166     if (iter == dependents_.end()) {
 167       eqIter = equivalenceBlock_.find(symbol);
 168       if (eqIter != equivalenceBlock_.end()) {
 169         DoEquivalenceBlockBase(symbol, eqIter->second);
 170       }
 171     } else {
 172       SymbolAndOffset &dep{iter->second};
 173       Symbol &base{*dep.symbol};
 174       if (const auto *baseBlock{FindCommonBlockContaining(base)}) {
 175         if (baseBlock == &commonBlock) {
 176           if (base.offset() != symbol.offset() - dep.offset ||
 177               llvm::is_contained(details.objects(), base)) {
 178             context_.Say(errorSite,
 179                 "'%s' is storage associated with '%s' by EQUIVALENCE elsewhere in COMMON block /%s/"_err_en_US,
 180                 symbol.name(), base.name(), commonBlock.name());
 181           }
 182         } else { // 8.10.3(1)
 183           context_.Say(errorSite,
 184               "'%s' in COMMON block /%s/ must not be storage associated with '%s' in COMMON block /%s/ by EQUIVALENCE"_err_en_US,
 185               symbol.name(), commonBlock.name(), base.name(),
 186               baseBlock->name());
 187         }
 188       } else if (dep.offset > symbol.offset()) { // 8.10.3(3)
 189         context_.Say(errorSite,
 190             "'%s' cannot backward-extend COMMON block /%s/ via EQUIVALENCE with '%s'"_err_en_US,
 191             symbol.name(), commonBlock.name(), base.name());
 192       } else {
 193         eqIter = equivalenceBlock_.find(base);
 194         base.get<ObjectEntityDetails>().set_commonBlock(commonBlock);
 195         base.set_offset(symbol.offset() - dep.offset);
 196       }
 197     }
 198     // Get full extent of any EQUIVALENCE block into size of COMMON ( see
 199     // 8.10.2.2 point 1 (2))
 200     if (eqIter != equivalenceBlock_.end()) {
 201       SizeAndAlignment &blockInfo{eqIter->second};
 202       minSize = std::max(
 203           minSize, std::max(offset_, eqIter->first->offset() + blockInfo.size));
 204       minAlignment = std::max(minAlignment, blockInfo.alignment);
 205     }
 206   }
 207   commonBlock.set_size(std::max(minSize, offset_));
 208   details.set_alignment(std::max(minAlignment, alignment_));
 209   context_.MapCommonBlockAndCheckConflicts(commonBlock);
 210 }
 211
 212 void ComputeOffsetsHelper::DoEquivalenceBlockBase(
 213     Symbol &symbol, SizeAndAlignment &blockInfo) {
 214   if (symbol.size() > blockInfo.size) {
 215     blockInfo.size = symbol.size();
 216   }
 217 }
 218
 219 void ComputeOffsetsHelper::DoEquivalenceSet(const EquivalenceSet &set) {
 220   std::vector<SymbolAndOffset> symbolOffsets;
 221   std::optional<std::size_t> representative;
 222   for (const EquivalenceObject &object : set) {
 223     std::size_t offset{ComputeOffset(object)};
 224     SymbolAndOffset resolved{
 225         Resolve(SymbolAndOffset{object.symbol, offset, object})};
 226     symbolOffsets.push_back(resolved);
 227     if (!representative ||
 228         resolved.offset >= symbolOffsets[*representative].offset) {
 229       // The equivalenced object with the largest offset from its resolved
 230       // symbol will be the representative of this set, since the offsets
 231       // of the other objects will be positive relative to it.
 232       representative = symbolOffsets.size() - 1;
 233     }
 234   }
 235   CHECK(representative);
 236   const SymbolAndOffset &base{symbolOffsets[*representative]};
 237   for (const auto &[symbol, offset, object] : symbolOffsets) {
 238     if (symbol == base.symbol) {
 239       if (offset != base.offset) {
 240         auto x{evaluate::OffsetToDesignator(
 241             context_.foldingContext(), *symbol, base.offset, 1)};
 242         auto y{evaluate::OffsetToDesignator(
 243             context_.foldingContext(), *symbol, offset, 1)};
 244         if (x && y) {
 245           context_
 246               .Say(base.object->source,
 247                   "'%s' and '%s' cannot have the same first storage unit"_err_en_US,
 248                   x->AsFortran(), y->AsFortran())
 249               .Attach(object->source, "Incompatible reference to '%s'"_en_US,
 250                   y->AsFortran());
 251         } else { // error recovery
 252           context_
 253               .Say(base.object->source,
 254                   "'%s' (offset %zd bytes and %zd bytes) cannot have the same first storage unit"_err_en_US,
 255                   symbol->name(), base.offset, offset)
 256               .Attach(object->source,
 257                   "Incompatible reference to '%s' offset %zd bytes"_en_US,
 258                   symbol->name(), offset);
 259         }
 260       }
 261     } else {
 262       dependents_.emplace(*symbol,
 263           SymbolAndOffset{*base.symbol, base.offset - offset, *object});
 264     }
 265   }
 266 }
 267
 268 // Offset of this equivalence object from the start of its variable.
 269 std::size_t ComputeOffsetsHelper::ComputeOffset(
 270     const EquivalenceObject &object) {
 271   std::size_t offset{0};
 272   if (!object.subscripts.empty()) {
 273     const ArraySpec &shape{object.symbol.get<ObjectEntityDetails>().shape()};
 274     auto lbound{[&](std::size_t i) {
 275       return *ToInt64(shape[i].lbound().GetExplicit());
 276     }};
 277     auto ubound{[&](std::size_t i) {
 278       return *ToInt64(shape[i].ubound().GetExplicit());
 279     }};
 280     for (std::size_t i{object.subscripts.size() - 1};;) {
 281       offset += object.subscripts[i] - lbound(i);
 282       if (i == 0) {
 283         break;
 284       }
 285       --i;
 286       offset *= ubound(i) - lbound(i) + 1;
 287     }
 288   }
 289   auto result{offset * GetSizeAndAlignment(object.symbol, false).size};
 290   if (object.substringStart) {
 291     int kind{context_.defaultKinds().GetDefaultKind(TypeCategory::Character)};
 292     if (const DeclTypeSpec * type{object.symbol.GetType()}) {
 293       if (const IntrinsicTypeSpec * intrinsic{type->AsIntrinsic()}) {
 294         kind = ToInt64(intrinsic->kind()).value_or(kind);
 295       }
 296     }
 297     result += kind * (*object.substringStart - 1);
 298   }
 299   return result;
 300 }
 301
 302 std::size_t ComputeOffsetsHelper::DoSymbol(Symbol &symbol) {
 303   if (!symbol.has<ObjectEntityDetails>() && !symbol.has<ProcEntityDetails>()) {
 304     return 0;
 305   }
 306   SizeAndAlignment s{GetSizeAndAlignment(symbol, true)};
 307   if (s.size == 0) {
 308     return 0;
 309   }
 310   std::size_t previousOffset{offset_};
 311   offset_ = Align(offset_, s.alignment);
 312   std::size_t padding{offset_ - previousOffset};
 313   symbol.set_size(s.size);
 314   symbol.set_offset(offset_);
 315   offset_ += s.size;
 316   alignment_ = std::max(alignment_, s.alignment);
 317   return padding;
 318 }
 319
 320 auto ComputeOffsetsHelper::GetSizeAndAlignment(
 321     const Symbol &symbol, bool entire) -> SizeAndAlignment {
 322   auto &targetCharacteristics{context_.targetCharacteristics()};
 323   if (IsDescriptor(symbol)) {
 324     auto dyType{evaluate::DynamicType::From(symbol)};
 325     const auto *derived{evaluate::GetDerivedTypeSpec(dyType)};
 326     int lenParams{derived ? CountLenParameters(*derived) : 0};
 327     bool needAddendum{derived || (dyType && dyType->IsUnlimitedPolymorphic())};
 328     std::size_t size{runtime::Descriptor::SizeInBytes(
 329         symbol.Rank(), needAddendum, lenParams)};
 330     return {size, targetCharacteristics.descriptorAlignment()};
 331   }
 332   if (IsProcedurePointer(symbol)) {
 333     return {targetCharacteristics.procedurePointerByteSize(),
 334         targetCharacteristics.procedurePointerAlignment()};
 335   }
 336   if (IsProcedure(symbol)) {
 337     return {};
 338   }
 339   auto &foldingContext{context_.foldingContext()};
 340   if (auto chars{evaluate::characteristics::TypeAndShape::Characterize(
 341           symbol, foldingContext)}) {
 342     if (entire) {
 343       if (auto size{ToInt64(chars->MeasureSizeInBytes(foldingContext))}) {
 344         return {static_cast<std::size_t>(*size),
 345             chars->type().GetAlignment(targetCharacteristics)};
 346       }
 347     } else { // element size only
 348       if (auto size{ToInt64(chars->MeasureElementSizeInBytes(
 349               foldingContext, true /*aligned*/))}) {
 350         return {static_cast<std::size_t>(*size),
 351             chars->type().GetAlignment(targetCharacteristics)};
 352       }
 353     }
 354   }
 355   return {};
 356 }
 357
 358 // Align a size to its natural alignment, up to maxAlignment.
 359 std::size_t ComputeOffsetsHelper::Align(std::size_t x, std::size_t alignment) {
 360   alignment =
 361       std::min(alignment, context_.targetCharacteristics().maxAlignment());
 362   return (x + alignment - 1) & -alignment;
 363 }
 364
 365 void ComputeOffsets(SemanticsContext &context, Scope &scope) {
 366   ComputeOffsetsHelper{context}.Compute(scope);
 367 }
 368
 369 } // namespace Fortran::semantics