[llvm] A Unified LTO Bitcode Frontend

Here's a high level summary of the changes in this patch. For more
information on rational, see the RFC.
(https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774).

  - Add config parameter to LTO backend, specifying which LTO mode is
    desired when using unified LTO.
  - Add unified LTO flag to the summary index for efficiency. Unified
    LTO modules can be detected without parsing the module.
  - Make sure that the ModuleID is generated by incorporating more types
    of symbols.

Differential Revision: https://reviews.llvm.org/D123803

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/IR/ModuleSummaryIndex.cpp b/llvm/lib/IR/ModuleSummaryIndex.cpp
index 7cba03e..15fe342 100644
--- a/llvm/lib/IR/ModuleSummaryIndex.cpp
+++ b/llvm/lib/IR/ModuleSummaryIndex.cpp
@@ -109,11 +109,13 @@ uint64_t ModuleSummaryIndex::getFlags() const {
     Flags |= 0x80;
   if (withSupportsHotColdNew())
     Flags |= 0x100;
+  if (hasUnifiedLTO())
+    Flags |= 0x200;
   return Flags;
 }
 
 void ModuleSummaryIndex::setFlags(uint64_t Flags) {
-  assert(Flags <= 0x1ff && "Unexpected bits in flag");
+  assert(Flags <= 0x2ff && "Unexpected bits in flag");
   // 1 bit: WithGlobalValueDeadStripping flag.
   // Set on combined index only.
   if (Flags & 0x1)
@@ -151,6 +153,10 @@ void ModuleSummaryIndex::setFlags(uint64_t Flags) {
   // Set on combined index only.
   if (Flags & 0x100)
     setWithSupportsHotColdNew();
+  // 1 bit: WithUnifiedLTO flag.
+  // Set on combined index only.
+  if (Flags & 0x200)
+    setUnifiedLTO();
 }
 
 // Collect for the given module the list of function it defines