AsmPrinter: Convert DIE::Values to a linked list

Change `DIE::Values` to a singly linked list, where each node is
allocated on a `BumpPtrAllocator`.  In order to support `push_back()`,
the list is circular, and points at the tail element instead of the
head.  I abstracted the core list logic out to `IntrusiveBackList` so
that it can be reused for `DIE::Children`, which also cares about
`push_back()`.

This drops llc memory usage from 799 MB down to 735 MB, about 8%.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)

llvm-svn: 240733

1 files changed, 6 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
index 80e9096bfea..30493c82565 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
@@ -165,18 +165,17 @@ void DIE::print(raw_ostream &O, unsigned IndentCount) const {
   }
 
   IndentCount += 2;
-  for (unsigned i = 0, N = Values.size(); i < N; ++i) {
+  unsigned I = 0;
+  for (const auto &V : Values) {
     O << Indent;
 
     if (!isBlock)
-      O << dwarf::AttributeString(Values[i].getAttribute());
+      O << dwarf::AttributeString(V.getAttribute());
     else
-      O << "Blk[" << i << "]";
+      O << "Blk[" << I++ << "]";
 
-    O <<  "  "
-      << dwarf::FormEncodingString(Values[i].getForm())
-      << " ";
-    Values[i].print(O);
+    O << "  " << dwarf::FormEncodingString(V.getForm()) << " ";
+    V.print(O);
     O << "\n";
   }
   IndentCount -= 2;