DwarfDebug: Emit number of bytes in .debug_loc entry directly

Emit the number of bytes in a `.debug_loc` entry directly.  The old code
created temp labels (expensive), emitted the difference between them,
and then emitted one on each side of the relevant bytes.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`
(the optimized version of ld64's `-save-temps` when linking the
`verify-uselistorder` executable in an LTO bootstrap).  I've hacked
`MCContext::Allocate()` to just call `malloc()` instead of using the
`BumpPtrAllocator` so that the heap profile is easier to read.  As far
as peak memory is concerned, `MCContext::Allocate()` is equivalent to a
leak, since it only gets freed at process teardown.

In my heap profile, this patch drops memory usage of
`DwarfDebug::emitDebugLoc()` from 132.56 MB (11.4%) down to 29.86 MB
(2.7%) at peak memory.  Some of that must be noise from `SmallVector`
(or other) allocations -- peak memory only dropped from 1160 MB down to
1100 MB -- but this nevertheless shaves 5% off the top.)

llvm-svn: 236629

1 files changed, 3 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 4fe4f26c923..e275d3aac7d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1545,16 +1545,13 @@ void DebugLocEntry::finalize(const AsmPrinter &AP, DebugLocStream &Locs,
 }
 
 void DwarfDebug::emitDebugLocEntryLocation(const DebugLocStream::Entry &Entry) {
+  // Emit the size.
   Asm->OutStreamer->AddComment("Loc expr size");
-  MCSymbol *begin = Asm->OutStreamer->getContext().CreateTempSymbol();
-  MCSymbol *end = Asm->OutStreamer->getContext().CreateTempSymbol();
-  Asm->EmitLabelDifference(end, begin, 2);
-  Asm->OutStreamer->EmitLabel(begin);
+  Asm->EmitInt16(DebugLocs.getBytes(Entry).size());
+
   // Emit the entry.
   APByteStreamer Streamer(*Asm);
   emitDebugLocEntry(Streamer, Entry);
-  // Close the range.
-  Asm->OutStreamer->EmitLabel(end);
 }
 
 // Emit locations into the debug loc section.