[MC] Ensure subsections have a MCDataFragment

Similar to 21fac2d1d060b0f9b11a746718e58d4cd1ee97e5 for sections. This
makes it feasible to cache the current fragment in MCStreamer.

1 files changed, 15 insertions, 3 deletions

diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index fec1cce..2357203 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -294,9 +294,21 @@ bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
   assert(Section && "Cannot switch to a null section!");
   getContext().clearDwarfLocSeen();
 
-  bool Created = getAssembler().registerSection(*Section);
-  Section->switchSubsection(Subsection);
-  return Created;
+  auto &Subsections = Section->Subsections;
+  size_t I = 0, E = Subsections.size();
+  while (I != E && Subsections[I].first < Subsection)
+    ++I;
+  // If the subsection number is not in the sorted Subsections list, create a
+  // new fragment list.
+  if (I == E || Subsections[I].first != Subsection) {
+    auto *F = getContext().allocFragment<MCDataFragment>();
+    F->setParent(Section);
+    Subsections.insert(Subsections.begin() + I,
+                       {Subsection, MCSection::FragList{F, F}});
+  }
+  Section->CurFragList = &Subsections[I].second;
+
+  return getAssembler().registerSection(*Section);
 }
 
 void MCObjectStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {