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
diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index cae73be..e5b749e 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -371,8 +371,10 @@
// 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 @@
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) {