[MC] Write padding into fragments when -mc-relax-all flag is used

Summary:
When instruction bundling is enabled and the -mc-relax-all flag is
set, we can write bundle padding directly into fragments and avoid
creating large number of fragments significantly reducing LLVM MC
memory usage.

Test Plan: Regression test attached

Reviewers: eliben

Subscribers: jfb, mseaborn

Differential Revision: http://reviews.llvm.org/D8072

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234714 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAsmLayout.h

@@ -50,11 +50,6 @@ private:
   /// \brief Is the layout for this fragment valid?
   bool isFragmentValid(const MCFragment *F) const;
 
-  /// \brief Compute the amount of padding required before this fragment to
-  /// obey bundling restrictions.
-  uint64_t computeBundlePadding(const MCFragment *F,
-                                uint64_t FOffset, uint64_t FSize);
-
 public:
   MCAsmLayout(MCAssembler &Assembler);
 

include/llvm/MC/MCAssembler.h

@@ -1245,11 +1245,23 @@ public:
       FileNames.push_back(FileName);
   }
 
+  /// \brief Write the necessary bundle padding to the given object writer.
+  /// Expects a fragment \p F containing instructions and its size \p FSize.
+  void writeFragmentPadding(const MCFragment &F, uint64_t FSize,
+                            MCObjectWriter *OW) const;
+
   /// @}
 
   void dump();
 };
 
+/// \brief Compute the amount of padding required before the fragment \p F to
+/// obey bundling restrictions, where \p FOffset is the fragment's offset in
+/// its section and \p FSize is the fragment's size.
+uint64_t computeBundlePadding(const MCAssembler &Assembler,
+                              const MCFragment *F,
+                              uint64_t FOffset, uint64_t FSize);
+
 } // end namespace llvm
 
 #endif

include/llvm/MC/MCELFStreamer.h

@@ -95,6 +95,9 @@ private:
 
   void fixSymbolsInTLSFixups(const MCExpr *expr);
 
+  /// \brief Merge the content of the fragment \p EF into the fragment \p DF.
+  void mergeFragment(MCDataFragment *, MCEncodedFragmentWithFixups *);
+
   bool SeenIdent;
 
   struct LocalCommon {
@@ -106,6 +109,10 @@ private:
   std::vector<LocalCommon> LocalCommons;
 
   SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
+
+  /// BundleGroups - The stack of fragments holding the bundle-locked
+  /// instructions.
+  llvm::SmallVector<MCDataFragment *, 4> BundleGroups;
 };
 
 MCELFStreamer *createARMELFStreamer(MCContext &Context, MCAsmBackend &TAB,

include/llvm/MC/MCObjectStreamer.h

@@ -44,10 +44,6 @@ class MCObjectStreamer : public MCStreamer {
   void EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) override;
   void EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) override;
 
-  // If any labels have been emitted but not assigned fragments, ensure that
-  // they get assigned, either to F if possible or to a new data fragment.
-  void flushPendingLabels(MCFragment *F);
-
 protected:
   MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB, raw_ostream &OS,
                    MCCodeEmitter *Emitter);
@@ -85,6 +81,12 @@ protected:
 
   bool changeSectionImpl(const MCSection *Section, const MCExpr *Subsection);
 
+  /// If any labels have been emitted but not assigned fragments, ensure that
+  /// they get assigned, either to F if possible or to a new data fragment.
+  /// Optionally, it is also possible to provide an offset \p FOffset, which
+  /// will be used as a symbol offset within the fragment.
+  void flushPendingLabels(MCFragment *F, uint64_t FOffset = 0);
+
 public:
   void visitUsedSymbol(const MCSymbol &Sym) override;