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