Bitcode: Add a string table to the bitcode format.

Add a top-level STRTAB block containing a string table blob, and start storing
strings for module codes FUNCTION, GLOBALVAR, ALIAS, IFUNC and COMDAT in
the string table.

This change allows us to share names between globals and comdats as well
as between modules, and improves the efficiency of loading bitcode files by
no longer using a bit encoding for symbol names. Once we start writing the
irsymtab to the bitcode file we will also be able to share strings between
it and the module.

On my machine, link time for Chromium for Linux with ThinLTO decreases by
about 7% for no-op incremental builds or about 1% for full builds. Total
bitcode file size decreases by about 3%.

As discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111732.html

Differential Revision: https://reviews.llvm.org/D31838

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300464 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp b/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
index abc6fa27a0e0..676134ca2368 100644
--- a/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
+++ b/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
@@ -122,6 +122,7 @@ static const char *GetBlockName(unsigned BlockID,
   case bitc::GLOBALVAL_SUMMARY_BLOCK_ID:
                                            return "GLOBALVAL_SUMMARY_BLOCK";
   case bitc::MODULE_STRTAB_BLOCK_ID:       return "MODULE_STRTAB_BLOCK";
+  case bitc::STRTAB_BLOCK_ID:              return "STRTAB_BLOCK";
   }
 }
 
@@ -315,6 +316,7 @@ static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
       STRINGIFY_CODE(FS, TYPE_CHECKED_LOAD_VCALLS)
       STRINGIFY_CODE(FS, TYPE_TEST_ASSUME_CONST_VCALL)
       STRINGIFY_CODE(FS, TYPE_CHECKED_LOAD_CONST_VCALL)
+      STRINGIFY_CODE(FS, VALUE_GUID)
     }
   case bitc::METADATA_ATTACHMENT_ID:
     switch(CodeID) {
@@ -381,6 +383,11 @@ static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
     default: return nullptr;
     case bitc::OPERAND_BUNDLE_TAG: return "OPERAND_BUNDLE_TAG";
     }
+  case bitc::STRTAB_BLOCK_ID:
+    switch(CodeID) {
+    default: return nullptr;
+    case bitc::STRTAB_BLOB: return "BLOB";
+    }
   }
 #undef STRINGIFY_CODE
 }