MC: Add MCAlignFragment::OnlyAlignAddress bit. This is a bit of magic that says the align fragment shouldn't contribute to the logical section size, it is will be used for cleaning up the code to handle section alignment.

llvm-svn: 103690

2 files changed, 28 insertions, 2 deletions

diff --git a/llvm/include/llvm/MC/MCAssembler.h b/llvm/include/llvm/MC/MCAssembler.h
index b641b0241d8..8918dbbb3c3 100644
--- a/llvm/include/llvm/MC/MCAssembler.h
+++ b/llvm/include/llvm/MC/MCAssembler.h
@@ -258,12 +258,19 @@ class MCAlignFragment : public MCFragment {
   /// target dependent.
   bool EmitNops : 1;
 
+  /// OnlyAlignAddress - Flag to indicate that this align is only used to adjust
+  /// the address space size of a section and that it should not be included as
+  /// part of the section size. This flag can only be used on the last fragment
+  /// in a section.
+  bool OnlyAlignAddress : 1;
+
 public:
   MCAlignFragment(unsigned _Alignment, int64_t _Value, unsigned _ValueSize,
                   unsigned _MaxBytesToEmit, MCSectionData *SD = 0)
     : MCFragment(FT_Align, SD), Alignment(_Alignment),
       Value(_Value),ValueSize(_ValueSize),
-      MaxBytesToEmit(_MaxBytesToEmit), EmitNops(false) {}
+      MaxBytesToEmit(_MaxBytesToEmit), EmitNops(false),
+      OnlyAlignAddress(false) {}
 
   /// @name Accessors
   /// @{
@@ -279,6 +286,9 @@ public:
   bool hasEmitNops() const { return EmitNops; }
   void setEmitNops(bool Value) { EmitNops = Value; }
 
+  bool hasOnlyAlignAddress() const { return OnlyAlignAddress; }
+  void setOnlyAlignAddress(bool Value) { OnlyAlignAddress = Value; }
+
   /// @}
 
   static bool classof(const MCFragment *F) {
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index ced395c5170..8086b3d4aea 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -392,6 +392,9 @@ void MCAssembler::LayoutFragment(MCAsmLayout &Layout, MCFragment &F) {
   case MCFragment::FT_Align: {
     MCAlignFragment &AF = cast<MCAlignFragment>(F);
 
+    assert((!AF.hasOnlyAlignAddress() || !AF.getNextNode()) &&
+           "Invalid OnlyAlignAddress bit, not the last fragment!");
+
     EffectiveSize = OffsetToAlignment(Address, AF.getAlignment());
     if (EffectiveSize > AF.getMaxBytesToEmit())
       EffectiveSize = 0;
@@ -474,9 +477,18 @@ void MCAssembler::LayoutSection(MCAsmLayout &Layout,
     MCFragment *F = &SD.getFragmentList().back();
     Size = Layout.getFragmentOffset(F) + Layout.getFragmentEffectiveSize(F);
   }
-  Layout.setSectionSize(&SD, Size);
   Layout.setSectionAddressSize(&SD, Size);
   Layout.setSectionFileSize(&SD, IsVirtual ? 0 : Size);
+
+  // Handle OnlyAlignAddress bit.
+  if (!SD.getFragmentList().empty()) {
+    MCAlignFragment *AF =
+      dyn_cast<MCAlignFragment>(&SD.getFragmentList().back());
+    if (AF && AF->hasOnlyAlignAddress())
+      Size -= Layout.getFragmentEffectiveSize(AF);
+  }
+
+  Layout.setSectionSize(&SD, Size);
 }
 
 /// WriteFragmentData - Write the \arg F data to the output file.
@@ -856,6 +868,10 @@ void MCAlignFragment::dump() {
 
   OS << "<MCAlignFragment ";
   this->MCFragment::dump();
+  if (hasEmitNops())
+    OS << " (emit nops)";
+  if (hasOnlyAlignAddress())
+    OS << " (only align section)";
   OS << "\n       ";
   OS << " Alignment:" << getAlignment()
      << " Value:" << getValue() << " ValueSize:" << getValueSize()