commit 77cfcd75092b57693d40123a013e59295634a945
author David Blaikie <dblaikie@gmail.com> Tue Nov 12 14:15:37 2019 -0800
committer David Blaikie <dblaikie@gmail.com> Fri Nov 15 18:51:13 2019 -0800
tree 1199d6a4ddee2a0351d11eacd99f2ec373a8f156
parent 97c742e6b74e731afdef74dd5f8366ce883e0520

DebugInfo: Use loclistx for DWARFv5 location lists to reduce the number of relocations

This only implements the non-dwo part, but loclistx is necessary to use
location lists in DWARFv5, so it's a precursor to that work - and
generally reduces relocations (only using one reloc, then
indexes/relative offsets for all location list references) in non-split
DWARF.

llvm/lib/CodeGen/AsmPrinter/DIE.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
index f4134da..c4d5b71 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
@@ -798,6 +798,8 @@
 //===----------------------------------------------------------------------===//
 
 unsigned DIELocList::SizeOf(const AsmPrinter *AP, dwarf::Form Form) const {
+  if (Form == dwarf::DW_FORM_loclistx)
+    return getULEB128Size(Index);
   if (Form == dwarf::DW_FORM_data4)
     return 4;
   if (Form == dwarf::DW_FORM_sec_offset)
@@ -808,6 +810,10 @@
 /// EmitValue - Emit label value.
 ///
 void DIELocList::EmitValue(const AsmPrinter *AP, dwarf::Form Form) const {
+  if (Form == dwarf::DW_FORM_loclistx) {
+    AP->EmitULEB128(Index);
+    return;
+  }
   DwarfDebug *DD = AP->getDwarfDebug();
   MCSymbol *Label = DD->getDebugLocs().getList(Index).Label;
   AP->emitDwarfSymbolReference(Label, /*ForceOffset*/ DD->useSplitDwarf());

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index a61c98e..9578e01 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -1220,8 +1220,11 @@
 /// Add a Dwarf loclistptr attribute data and value.
 void DwarfCompileUnit::addLocationList(DIE &Die, dwarf::Attribute Attribute,
                                        unsigned Index) {
-  dwarf::Form Form = DD->getDwarfVersion() >= 4 ? dwarf::DW_FORM_sec_offset
-                                                : dwarf::DW_FORM_data4;
+  dwarf::Form Form = dwarf::DW_FORM_data4;
+  if (DD->getDwarfVersion() == 4)
+    Form =dwarf::DW_FORM_sec_offset;
+  if (DD->getDwarfVersion() >= 5)
+    Form =dwarf::DW_FORM_loclistx;
   Die.addValue(DIEValueAllocator, Attribute, Form, DIELocList(Index));
 }
 

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index c240099..d9b5eb1 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2323,9 +2323,12 @@
   // FIXME: Generate the offsets table and use DW_FORM_loclistx with the
   // DW_AT_loclists_base attribute. Until then set the number of offsets to 0.
   Asm->OutStreamer->AddComment("Offset entry count");
-  Asm->emitInt32(0);
+  Asm->emitInt32(DebugLocs.getLists().size());
   Asm->OutStreamer->EmitLabel(DebugLocs.getSym());
 
+  for (const auto &List : DebugLocs.getLists())
+    Asm->EmitLabelDifference(List.Label, DebugLocs.getSym(), 4);
+
   return TableEnd;
 }