Optimize the memory usage of MC bundling, by creating a new type of fragment

into which we can emit single instructions without fixups (which is most
instructions). This is an optimization required because MCDataFragment
is prety large (240 bytes on x64), with no change in functionality.

For large programs, this reduces memory usage overhead required for bundling
by 40%.

To make the code as palatable as possible, the MCEncodedFragment interface was
further fragmented (no pun intended) and MCEncodedFragmentWithFixups is used
as the interface to work against when the user expects fixups. MCDataFragment
and MCRelaxableFragment implement this interface, while the new
MCCompactEncodedInstFragment implements MCEncodeFragment.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172572 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 2 deletions

diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index cae73be298..e5b749e28b 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -371,8 +371,10 @@ void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
   // data fragment).
   //
   // If bundling is enabled:
-  // - If we're not in a bundle-locked group, emit the instruction into a data
-  //   fragment of its own.
+  // - If we're not in a bundle-locked group, emit the instruction into a
+  //   fragment of its own. If there are no fixups registered for the
+  //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
+  //   MCDataFragment.
   // - If we're in a bundle-locked group, append the instruction to the current
   //   data fragment because we want all the instructions in a group to get into
   //   the same fragment. Be careful not to do that for the first instruction in
@@ -383,6 +385,14 @@ void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
     MCSectionData *SD = getCurrentSectionData();
     if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
       DF = getOrCreateDataFragment();
+    else if (!SD->isBundleLocked() && Fixups.size() == 0) {
+      // Optimize memory usage by emitting the instruction to a
+      // MCCompactEncodedInstFragment when not in a bundle-locked group and
+      // there are no fixups registered.
+      MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment(SD);
+      CEIF->getContents().append(Code.begin(), Code.end());
+      return;
+    }
     else {
       DF = new MCDataFragment(SD);
       if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {