ThinLTO: add early "dead-stripping" on the Index
Summary:
Using the linker-supplied list of "preserved" symbols, we can compute
the list of "dead" symbols, i.e. the one that are not reachable from
a "preserved" symbol transitively on the reference graph.
Right now we are using this information to mark these functions as
non-eligible for import.
The impact is two folds:
- Reduction of compile time: we don't import these functions anywhere
or import the function these symbols are calling.
- The limited number of import/export leads to better internalization.
Patch originally by Mehdi Amini.
Reviewers: mehdi_amini, pcc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D23488
llvm-svn: 291177
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 19a8e24..ebb2022 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -972,6 +972,7 @@
uint64_t RawFlags = 0;
RawFlags |= Flags.NotEligibleToImport; // bool
+ RawFlags |= (Flags.LiveRoot << 1);
// Linkage don't need to be remapped at that time for the summary. Any future
// change to the getEncodedLinkage() function will need to be taken into
// account here as well.