DwarfDebug: emit type units immediately.

Rather than storing type units in a vector and emitting them at the end
of code generation, emit them immediately and destroy them, reclaiming the
memory we were using for their DIEs.

In one benchmark carried out against Chromium's 50 largest (by bitcode
file size) translation units, total peak memory consumption with type units
decreased by median 17%, or by 7% when compared against disabling type units.

Tested using check-{llvm,clang}, the GDB 7.5 test suite (with
'-fdebug-types-section') and by eyeballing llvm-dwarfdump output on those
Chromium translation units with split DWARF both disabled and enabled, and
verifying that the only changes were to addresses and abbreviation ordering.

Differential Revision: http://reviews.llvm.org/D17118

llvm-svn: 260578

1 files changed, 17 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index ec7329eafb7..9b376827e54 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1628,9 +1628,10 @@ void DwarfDebug::emitDebugARanges() {
   }
 
   // Sort the CU list (again, to ensure consistent output order).
-  std::sort(CUs.begin(), CUs.end(), [](const DwarfUnit *A, const DwarfUnit *B) {
-    return A->getUniqueID() < B->getUniqueID();
-  });
+  std::sort(CUs.begin(), CUs.end(),
+            [](const DwarfCompileUnit *A, const DwarfCompileUnit *B) {
+              return A->getUniqueID() < B->getUniqueID();
+            });
 
   // Emit an arange table for each CU we used.
   for (DwarfCompileUnit *CU : CUs) {
@@ -1793,7 +1794,7 @@ void DwarfDebug::emitDebugMacinfo() {
 // DWARF5 Experimental Separate Dwarf emitters.
 
 void DwarfDebug::initSkeletonUnit(const DwarfUnit &U, DIE &Die,
-                                  std::unique_ptr<DwarfUnit> NewU) {
+                                  std::unique_ptr<DwarfCompileUnit> NewU) {
   NewU->addString(Die, dwarf::DW_AT_GNU_dwo_name,
                   U.getCUNode()->getSplitDebugFilename());
 
@@ -1882,21 +1883,19 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
   if (!TypeUnitsUnderConstruction.empty() && AddrPool.hasBeenUsed())
     return;
 
-  const DwarfTypeUnit *&TU = DwarfTypeUnits[CTy];
-  if (TU) {
-    CU.addDIETypeSignature(RefDie, *TU);
+  auto Ins = TypeSignatures.insert(std::make_pair(CTy, 0));
+  if (!Ins.second) {
+    CU.addDIETypeSignature(RefDie, Ins.first->second);
     return;
   }
 
   bool TopLevelType = TypeUnitsUnderConstruction.empty();
   AddrPool.resetUsedFlag();
 
-  auto OwnedUnit = make_unique<DwarfTypeUnit>(
-      InfoHolder.getUnits().size() + TypeUnitsUnderConstruction.size(), CU, Asm,
-      this, &InfoHolder, getDwoLineTable(CU));
+  auto OwnedUnit = make_unique<DwarfTypeUnit>(CU, Asm, this, &InfoHolder,
+                                              getDwoLineTable(CU));
   DwarfTypeUnit &NewTU = *OwnedUnit;
   DIE &UnitDie = NewTU.getUnitDie();
-  TU = &NewTU;
   TypeUnitsUnderConstruction.push_back(
       std::make_pair(std::move(OwnedUnit), CTy));
 
@@ -1905,6 +1904,7 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
 
   uint64_t Signature = makeTypeSignature(Identifier);
   NewTU.setTypeSignature(Signature);
+  Ins.first->second = Signature;
 
   if (useSplitDwarf())
     NewTU.initSection(Asm->getObjFileLowering().getDwarfTypesDWOSection());
@@ -1928,7 +1928,7 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
       // This is pessimistic as some of these types might not be dependent on
       // the type that used an address.
       for (const auto &TU : TypeUnitsToAdd)
-        DwarfTypeUnits.erase(TU.second);
+        TypeSignatures.erase(TU.second);
 
       // Construct this type in the CU directly.
       // This is inefficient because all the dependent types will be rebuilt
@@ -1940,10 +1940,12 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
 
     // If the type wasn't dependent on fission addresses, finish adding the type
     // and all its dependent types.
-    for (auto &TU : TypeUnitsToAdd)
-      InfoHolder.addUnit(std::move(TU.first));
+    for (auto &TU : TypeUnitsToAdd) {
+      InfoHolder.computeSizeAndOffsetsForUnit(TU.first.get());
+      InfoHolder.emitUnit(TU.first.get(), useSplitDwarf());
+    }
   }
-  CU.addDIETypeSignature(RefDie, NewTU);
+  CU.addDIETypeSignature(RefDie, Signature);
 }
 
 // Accelerator table mutators - add each name along with its companion