DebugInfo: Support debug_loc under fission

Implement debug_loc.dwo, as well as llvm-dwarfdump support for dumping
this section.

Outlined in the DWARF5 spec and http://gcc.gnu.org/wiki/DebugFission the
debug_loc.dwo section has more variation than the standard debug_loc,
allowing 3 different forms of entry (plus the end of list entry). GCC
seems to, and Clang certainly, only use one form, so I've just
implemented dumping support for that for now.

It wasn't immediately obvious that there was a good refactoring to share
the implementation of dumping support between debug_loc and
debug_loc.dwo, so they're separate for now - ideas welcome or I may come
back to it at some point.

As per a comment in the code, we could choose different forms that may
reduce the number of debug_addr entries we emit, but that will require
further study.

llvm-svn: 204697

1 files changed, 24 insertions, 10 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 792a9c48cdf..a9ed9dbcb5b 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -184,7 +184,7 @@ DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
 
   DwarfInfoSectionSym = DwarfAbbrevSectionSym = DwarfStrSectionSym = 0;
   DwarfDebugRangeSectionSym = DwarfDebugLocSectionSym = DwarfLineSectionSym = 0;
-  DwarfAddrSectionSym = 0;
+  DwarfAddrSectionSym = DwarfDebugLocDWOSectionSym = 0;
   DwarfAbbrevDWOSectionSym = DwarfStrDWOSectionSym = 0;
   FunctionBeginSym = FunctionEndSym = 0;
   CurFn = 0;
@@ -1865,7 +1865,6 @@ void DwarfDebug::emitSectionLabels() {
 
   DwarfLineSectionSym =
       emitSectionSym(Asm, TLOF.getDwarfLineSection(), "section_line");
-  emitSectionSym(Asm, TLOF.getDwarfLocSection());
   if (GenerateGnuPubSections) {
     DwarfGnuPubNamesSectionSym =
         emitSectionSym(Asm, TLOF.getDwarfGnuPubNamesSection());
@@ -1883,12 +1882,13 @@ void DwarfDebug::emitSectionLabels() {
         emitSectionSym(Asm, TLOF.getDwarfStrDWOSection(), "skel_string");
     DwarfAddrSectionSym =
         emitSectionSym(Asm, TLOF.getDwarfAddrSection(), "addr_sec");
-  }
+    DwarfDebugLocDWOSectionSym =
+        emitSectionSym(Asm, TLOF.getDwarfLocDWOSection(), "skel_loc");
+  } else
+    DwarfDebugLocSectionSym =
+        emitSectionSym(Asm, TLOF.getDwarfLocSection(), "section_debug_loc");
   DwarfDebugRangeSectionSym =
       emitSectionSym(Asm, TLOF.getDwarfRangesSection(), "debug_range");
-
-  DwarfDebugLocSectionSym =
-      emitSectionSym(Asm, TLOF.getDwarfLocSection(), "section_debug_loc");
 }
 
 // Recursively emits a debug information entry.
@@ -2379,7 +2379,8 @@ void DwarfDebug::emitDebugLocEntry(ByteStreamer &Streamer,
 void DwarfDebug::emitDebugLoc() {
   // Start the dwarf loc section.
   Asm->OutStreamer.SwitchSection(
-      Asm->getObjFileLowering().getDwarfLocSection());
+      useSplitDwarf() ? Asm->getObjFileLowering().getDwarfLocDWOSection()
+                      : Asm->getObjFileLowering().getDwarfLocSection());
   unsigned char Size = Asm->getDataLayout().getPointerSize();
   unsigned index = 0;
   for (const auto &DebugLoc : DotDebugLocEntries) {
@@ -2389,7 +2390,16 @@ void DwarfDebug::emitDebugLoc() {
       // compile unit. This is a hard coded 0 for low_pc when we're emitting
       // ranges, or the DW_AT_low_pc on the compile unit otherwise.
       const DwarfCompileUnit *CU = Entry.getCU();
-      if (CU->getRanges().size() == 1) {
+      if (useSplitDwarf()) {
+        // Just always use start_length for now - at least that's one address
+        // rather than two. We could get fancier and try to, say, reuse an
+        // address we know we've emitted elsewhere (the start of the function?
+        // The start of the CU or CU subrange that encloses this range?)
+        Asm->EmitInt8(dwarf::DW_LLE_start_length_entry);
+        unsigned idx = InfoHolder.getAddrPoolIndex(Entry.getBeginSym());
+        Asm->EmitULEB128(idx);
+        Asm->EmitLabelDifference(Entry.getEndSym(), Entry.getBeginSym(), 4);
+      } else if (CU->getRanges().size() == 1) {
         // Grab the begin symbol from the first range as our base.
         const MCSymbol *Base = CU->getRanges()[0].getStart();
         Asm->EmitLabelDifference(Entry.getBeginSym(), Base, Size);
@@ -2409,8 +2419,12 @@ void DwarfDebug::emitDebugLoc() {
       // Close the range.
       Asm->OutStreamer.EmitLabel(end);
     }
-    Asm->OutStreamer.EmitIntValue(0, Size);
-    Asm->OutStreamer.EmitIntValue(0, Size);
+    if (useSplitDwarf())
+      Asm->EmitInt8(dwarf::DW_LLE_end_of_list_entry);
+    else {
+      Asm->OutStreamer.EmitIntValue(0, Size);
+      Asm->OutStreamer.EmitIntValue(0, Size);
+    }
     ++index;
   }
 }