Sorry for such a large commit. The summary is that only MachO cares about the

actuall addresses in a .o file, so it is better to let the MachO writer compute
it.

This is good for two reasons. First, areas that shouldn't care about
addresses now don't have access to it. Second, the layout of each section
is independent. I should use this in a subsequent commit to speed it up.

Most of the patch is just removing the section address computation. The two
interesting parts are the change on how we handle padding in the end
of sections and how MachO can get the address of a-b when a and b are in
different sections.

Since now the expression evaluation normally doesn't know the section address,
it will think that a-b needs relocation and let the MachO writer know. Once
it has computed the section addresses, it calls back the expression evaluation
with the section addresses to resolve these expressions.

The remaining problem is the handling of padding. Currently it will create
a special alignment fragment at the end. Since that fragment doesn't update
the alignment of the section, it needs the real address to be computed.

Since now the layout will not compute a-b with a and b in different sections,
the only effect that the special alignment fragment has is update the
address size of the section. This can also be done by the MachO writer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121076 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 107 deletions

diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 299eb0ab67..4f63a081ae 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -38,7 +38,6 @@ STATISTIC(FragmentLayouts, "Number of fragment layouts");
 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
-STATISTIC(SectionLayouts, "Number of section layouts");
 }
 }
 
@@ -113,11 +112,6 @@ void MCAsmLayout::EnsureValid(const MCFragment *F) const {
   }
 }
 
-uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
-  assert(F->getParent() && "Missing section()!");
-  return getSectionAddress(F->getParent()) + getFragmentOffset(F);
-}
-
 uint64_t MCAsmLayout::getFragmentEffectiveSize(const MCFragment *F) const {
   EnsureValid(F);
   assert(F->EffectiveSize != ~UINT64_C(0) && "Address not set!");
@@ -135,17 +129,6 @@ uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
   return getFragmentOffset(SD->getFragment()) + SD->getOffset();
 }
 
-uint64_t MCAsmLayout::getSymbolAddress(const MCSymbolData *SD) const {
-  assert(SD->getFragment() && "Invalid getAddress() on undefined symbol!");
-  return getFragmentAddress(SD->getFragment()) + SD->getOffset();
-}
-
-uint64_t MCAsmLayout::getSectionAddress(const MCSectionData *SD) const {
-  EnsureValid(SD->begin());
-  assert(SD->Address != ~UINT64_C(0) && "Address not set!");
-  return SD->Address;
-}
-
 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
   // The size is the last fragment's end offset.
   const MCFragment &F = SD->getFragmentList().back();
@@ -161,17 +144,6 @@ uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
   return getSectionAddressSize(SD);
 }
 
-uint64_t MCAsmLayout::getSectionSize(const MCSectionData *SD) const {
-  // The logical size is the address space size minus any tail padding.
-  uint64_t Size = getSectionAddressSize(SD);
-  const MCAlignFragment *AF =
-    dyn_cast<MCAlignFragment>(&(SD->getFragmentList().back()));
-  if (AF && AF->hasOnlyAlignAddress())
-    Size -= getFragmentEffectiveSize(AF);
-
-  return Size;
-}
-
 /* *** */
 
 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
@@ -196,7 +168,6 @@ MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
   : Section(&_Section),
     Ordinal(~UINT32_C(0)),
     Alignment(1),
-    Address(~UINT64_C(0)),
     HasInstructions(false)
 {
   if (A)
@@ -221,11 +192,9 @@ MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
 /* *** */
 
 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
-                         MCCodeEmitter &_Emitter, bool _PadSectionToAlignment,
-                         raw_ostream &_OS)
+                         MCCodeEmitter &_Emitter, raw_ostream &_OS)
   : Context(_Context), Backend(_Backend), Emitter(_Emitter),
-    OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false),
-    PadSectionToAlignment(_PadSectionToAlignment)
+    OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false)
 {
 }
 
@@ -285,14 +254,14 @@ bool MCAssembler::EvaluateFixup(const MCObjectWriter &Writer,
   if (const MCSymbolRefExpr *A = Target.getSymA()) {
     const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
     if (Sym.isDefined())
-      Value += Layout.getSymbolAddress(&getSymbolData(Sym));
+      Value += Layout.getSymbolOffset(&getSymbolData(Sym));
     else
       IsResolved = false;
   }
   if (const MCSymbolRefExpr *B = Target.getSymB()) {
     const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
     if (Sym.isDefined())
-      Value -= Layout.getSymbolAddress(&getSymbolData(Sym));
+      Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
     else
       IsResolved = false;
   }
@@ -301,13 +270,12 @@ bool MCAssembler::EvaluateFixup(const MCObjectWriter &Writer,
     IsResolved = Writer.IsFixupFullyResolved(*this, Target, IsPCRel, DF);
 
   if (IsPCRel)
-    Value -= Layout.getFragmentAddress(DF) + Fixup.getOffset();
+    Value -= Layout.getFragmentOffset(DF) + Fixup.getOffset();
 
   return IsResolved;
 }
 
 uint64_t MCAssembler::ComputeFragmentSize(const MCFragment &F,
-                                          uint64_t SectionAddress,
                                           uint64_t FragmentOffset) const {
   switch (F.getKind()) {
   case MCFragment::FT_Data:
@@ -323,11 +291,7 @@ uint64_t MCAssembler::ComputeFragmentSize(const MCFragment &F,
   case MCFragment::FT_Align: {
     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
 
-    assert((!AF.hasOnlyAlignAddress() || !AF.getNextNode()) &&
-           "Invalid OnlyAlignAddress bit, not the last fragment!");
-
-    uint64_t Size = OffsetToAlignment(SectionAddress + FragmentOffset,
-                                      AF.getAlignment());
+    uint64_t Size = OffsetToAlignment(FragmentOffset, AF.getAlignment());
 
     // Honor MaxBytesToEmit.
     if (Size > AF.getMaxBytesToEmit())
@@ -351,8 +315,6 @@ void MCAsmLayout::LayoutFile() {
   // Initialize the first section and set the valid fragment layout point. All
   // actual layout computations are done lazily.
   LastValidFragment = 0;
-  if (!getSectionOrder().empty())
-    getSectionOrder().front()->Address = 0;
 }
 
 void MCAsmLayout::LayoutFragment(MCFragment *F) {
@@ -371,43 +333,14 @@ void MCAsmLayout::LayoutFragment(MCFragment *F) {
 
   ++stats::FragmentLayouts;
 
-  // Compute the fragment start address.
-  uint64_t StartAddress = F->getParent()->Address;
-  uint64_t Address = StartAddress;
+  // Compute fragment offset and size.
+  uint64_t Offset = 0;
   if (Prev)
-    Address += Prev->Offset + Prev->EffectiveSize;
+    Offset += Prev->Offset + Prev->EffectiveSize;
 
-  // Compute fragment offset and size.
-  F->Offset = Address - StartAddress;
-  F->EffectiveSize = getAssembler().ComputeFragmentSize(*F, StartAddress,
-                                                        F->Offset);
+  F->Offset = Offset;
+  F->EffectiveSize = getAssembler().ComputeFragmentSize(*F, F->Offset);
   LastValidFragment = F;
-
-  // If this is the last fragment in a section, update the next section address.
-  if (!F->getNextNode()) {
-    unsigned NextIndex = F->getParent()->getLayoutOrder() + 1;
-    if (NextIndex != getSectionOrder().size())
-      LayoutSection(getSectionOrder()[NextIndex]);
-  }
-}
-
-void MCAsmLayout::LayoutSection(MCSectionData *SD) {
-  unsigned SectionOrderIndex = SD->getLayoutOrder();
-
-  ++stats::SectionLayouts;
-
-  // Compute the section start address.
-  uint64_t StartAddress = 0;
-  if (SectionOrderIndex) {
-    MCSectionData *Prev = getSectionOrder()[SectionOrderIndex - 1];
-    StartAddress = getSectionAddress(Prev) + getSectionAddressSize(Prev);
-  }
-
-  // Honor the section alignment requirements.
-  StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
-
-  // Set the section address.
-  SD->Address = StartAddress;
 }
 
 /// WriteFragmentData - Write the \arg F data to the output file.
@@ -566,7 +499,7 @@ void MCAssembler::WriteSectionData(const MCSectionData *SD,
          ie = SD->end(); it != ie; ++it)
     WriteFragmentData(*this, Layout, *it, OW);
 
-  assert(OW->getStream().tell() - Start == Layout.getSectionFileSize(SD));
+  assert(OW->getStream().tell() - Start == Layout.getSectionAddressSize(SD));
 }
 
 
@@ -594,29 +527,7 @@ void MCAssembler::Finish(MCObjectWriter *Writer) {
   // Create the layout object.
   MCAsmLayout Layout(*this);
 
-  // Insert additional align fragments for concrete sections to explicitly pad
-  // the previous section to match their alignment requirements. This is for
-  // 'gas' compatibility, it shouldn't strictly be necessary.
-  if (PadSectionToAlignment) {
-    for (unsigned i = 1, e = Layout.getSectionOrder().size(); i < e; ++i) {
-      MCSectionData *SD = Layout.getSectionOrder()[i];
-
-      // Ignore sections without alignment requirements.
-      unsigned Align = SD->getAlignment();
-      if (Align <= 1)
-        continue;
-
-      // Ignore virtual sections, they don't cause file size modifications.
-      if (SD->getSection().isVirtualSection())
-        continue;
-
-      // Otherwise, create a new align fragment at the end of the previous
-      // section.
-      MCAlignFragment *AF = new MCAlignFragment(Align, 0, 1, Align,
-                                                Layout.getSectionOrder()[i - 1]);
-      AF->setOnlyAlignAddress(true);
-    }
-  }
+
 
   // Create dummy fragments and assign section ordinals.
   unsigned SectionIndex = 0;
@@ -668,7 +579,7 @@ void MCAssembler::Finish(MCObjectWriter *Writer) {
 
   // Allow the object writer a chance to perform post-layout binding (for
   // example, to set the index fields in the symbol data).
-  Writer->ExecutePostLayoutBinding(*this);
+  Writer->ExecutePostLayoutBinding(*this, Layout);
 
   // Evaluate and apply the fixups, generating relocation entries as necessary.
   for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
@@ -920,8 +831,6 @@ void MCFragment::dump() {
     const MCAlignFragment *AF = cast<MCAlignFragment>(this);
     if (AF->hasEmitNops())
       OS << " (emit nops)";
-    if (AF->hasOnlyAlignAddress())
-      OS << " (only align section)";
     OS << "\n       ";
     OS << " Alignment:" << AF->getAlignment()
        << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
@@ -991,8 +900,7 @@ void MCSectionData::dump() {
   raw_ostream &OS = llvm::errs();
 
   OS << "<MCSectionData";
-  OS << " Alignment:" << getAlignment() << " Address:" << Address
-     << " Fragments:[\n      ";
+  OS << " Alignment:" << getAlignment() << " Fragments:[\n      ";
   for (iterator it = begin(), ie = end(); it != ie; ++it) {
     if (it != begin()) OS << ",\n      ";
     it->dump();