[CodeGen] Generate DWARF v5 Accelerator Tables

Summary:
This patch adds a DwarfAccelTableEmitter class, which generates an
accelerator table, as specified in DWARF v5 standard. At the moment it
only generates a DIE offset column and (if we are indexing more than one
compile unit) a CU column.

Indexing type units is not currently supported, as we don't even have
the ability to generate DWARF v5-compatible compile units.

The implementation is not data-source agnostic like the one generating
apple tables. This was not necessary as we currently only have one user
of this code, and without a second user it was not obvious to me how to
best abstract this. (The difference between these tables and the apple
ones is that they need a lot more metadata about the debug info they are
indexing).

The generation is triggered by the --accel-tables argument, which
supersedes the --dwarf-accel-tables arg -- the latter was a simple
on-off switch, but not we can choose between two kinds of accelerator
tables we can generate.

This is tested by parsing the generated tables with llvm-dwarfdump and
the DWARFVerifier, and I've also checked that GNU readelf is able to
make sense of the tables.

Differential Revision: https://reviews.llvm.org/D43286

llvm-svn: 329179

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index 83da8ac..b154c98 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -201,6 +201,9 @@ void MCObjectFileInfo::initMachOMCObjectFileInfo(const Triple &T) {
   }
 
   // Debug Information.
+  DwarfDebugNamesSection =
+      Ctx->getMachOSection("__DWARF", "__debug_names", MachO::S_ATTR_DEBUG,
+                           SectionKind::getMetadata(), "debug_names_begin");
   DwarfAccelNamesSection =
       Ctx->getMachOSection("__DWARF", "__apple_names", MachO::S_ATTR_DEBUG,
                            SectionKind::getMetadata(), "names_begin");
@@ -558,6 +561,8 @@ void MCObjectFileInfo::initELFMCObjectFileInfo(const Triple &T, bool Large) {
   // DWARF5 Experimental Debug Info
 
   // Accelerator Tables
+  DwarfDebugNamesSection =
+      Ctx->getELFSection(".debug_names", ELF::SHT_PROGBITS, 0);
   DwarfAccelNamesSection =
       Ctx->getELFSection(".apple_names", ELF::SHT_PROGBITS, 0);
   DwarfAccelObjCSection =
@@ -795,6 +800,11 @@ void MCObjectFileInfo::initCOFFMCObjectFileInfo(const Triple &T) {
       COFF::IMAGE_SCN_MEM_DISCARDABLE | COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
           COFF::IMAGE_SCN_MEM_READ,
       SectionKind::getMetadata());
+  DwarfDebugNamesSection = Ctx->getCOFFSection(
+      ".debug_names",
+      COFF::IMAGE_SCN_MEM_DISCARDABLE | COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+          COFF::IMAGE_SCN_MEM_READ,
+      SectionKind::getMetadata(), "debug_names_begin");
   DwarfAccelNamesSection = Ctx->getCOFFSection(
       ".apple_names",
       COFF::IMAGE_SCN_MEM_DISCARDABLE | COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |