lld/wasm/OutputSegment.cpp

   1 //===- OutputSegment.h -----------------------------------------*- 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 "OutputSegment.h"
  10 #include "InputChunks.h"
  11 #include "lld/Common/Memory.h"
  12
  13 #define DEBUG_TYPE "lld"
  14
  15 using namespace llvm;
  16 using namespace llvm::wasm;
  17
  18 namespace lld {
  19
  20 namespace wasm {
  21
  22 void OutputSegment::addInputSegment(InputChunk *inSeg) {
  23   alignment = std::max(alignment, inSeg->alignment);
  24   inputSegments.push_back(inSeg);
  25   size = llvm::alignTo(size, 1ULL << inSeg->alignment);
  26   LLVM_DEBUG(dbgs() << "addInputSegment: " << inSeg->getName()
  27                     << " oname=" << name << " size=" << inSeg->getSize()
  28                     << " align=" << inSeg->alignment << " at:" << size << "\n");
  29   inSeg->outputSeg = this;
  30   inSeg->outputSegmentOffset = size;
  31   size += inSeg->getSize();
  32 }
  33
  34 // This function scans over the input segments.
  35 //
  36 // It removes MergeInputChunks from the input section array and adds
  37 // new synthetic sections at the location of the first input section
  38 // that it replaces. It then finalizes each synthetic section in order
  39 // to compute an output offset for each piece of each input section.
  40 void OutputSegment::finalizeInputSegments() {
  41   LLVM_DEBUG(llvm::dbgs() << "finalizeInputSegments: " << name << "\n");
  42   std::vector<SyntheticMergedChunk *> mergedSegments;
  43   std::vector<InputChunk *> newSegments;
  44   for (InputChunk *s : inputSegments) {
  45     MergeInputChunk *ms = dyn_cast<MergeInputChunk>(s);
  46     if (!ms) {
  47       newSegments.push_back(s);
  48       continue;
  49     }
  50
  51     // A segment should not make it here unless its alive
  52     assert(ms->live);
  53
  54     auto i = llvm::find_if(mergedSegments, [=](SyntheticMergedChunk *seg) {
  55       return seg->flags == ms->flags && seg->alignment == ms->alignment;
  56     });
  57     if (i == mergedSegments.end()) {
  58       LLVM_DEBUG(llvm::dbgs() << "new merge segment: " << name
  59                               << " alignment=" << ms->alignment << "\n");
  60       auto *syn = make<SyntheticMergedChunk>(name, ms->alignment, ms->flags);
  61       syn->outputSeg = this;
  62       mergedSegments.push_back(syn);
  63       i = std::prev(mergedSegments.end());
  64       newSegments.push_back(syn);
  65     } else {
  66       LLVM_DEBUG(llvm::dbgs() << "adding to merge segment: " << name << "\n");
  67     }
  68     (*i)->addMergeChunk(ms);
  69   }
  70
  71   for (auto *ms : mergedSegments)
  72     ms->finalizeContents();
  73
  74   inputSegments = newSegments;
  75   size = 0;
  76   for (InputChunk *seg : inputSegments) {
  77     size = llvm::alignTo(size, 1ULL << seg->alignment);
  78     LLVM_DEBUG(llvm::dbgs() << "outputSegmentOffset set: " << seg->getName()
  79                             << " -> " << size << "\n");
  80     seg->outputSegmentOffset = size;
  81     size += seg->getSize();
  82   }
  83 }
  84
  85 } // namespace wasm
  86 } // namespace lld