forked from OSchip/llvm-project
d5a70db193
Before this, if an inline function was defined in several input files, lld would write each copy of the inline function the output. With this patch, it only writes one copy. Reduces the size of Chromium Framework from 378MB to 345MB (compared to 290MB linked with ld64, which also does dead-stripping, which we don't do yet), and makes linking it faster: N Min Max Median Avg Stddev x 10 3.9957051 4.3496981 4.1411121 4.156837 0.10092097 + 10 3.908154 4.169318 3.9712729 3.9846753 0.075773012 Difference at 95.0% confidence -0.172162 +/- 0.083847 -4.14165% +/- 2.01709% (Student's t, pooled s = 0.0892373) Implementation-wise, when merging two weak symbols, this sets a "canOmitFromOutput" on the InputSection belonging to the weak symbol not put in the symbol table. We then don't write InputSections that have this set, as long as they are not referenced from other symbols. (This happens e.g. for object files that don't set .subsections_via_symbols or that use .alt_entry.) Some restrictions: - not yet done for bitcode inputs - no "comdat" handling (`kindNoneGroupSubordinate*` in ld64) -- Frame Descriptor Entries (FDEs), Language Specific Data Areas (LSDAs) (that is, catch block unwind information) and Personality Routines associated with weak functions still not stripped. This is wasteful, but harmless. - However, this does strip weaks from __unwind_info (which is needed for correctness and not just for size) - This nopes out on InputSections that are referenced form more than one symbol (eg from .alt_entry) for now Things that work based on symbols Just Work: - map files (change in MapFile.cpp is no-op and not needed; I just found it a bit more explicit) - exports Things that work with inputSections need to explicitly check if an inputSection is written (e.g. unwind info). This patch is useful in itself, but it's also likely also a useful foundation for dead_strip. I used to have a "canoncialRepresentative" pointer on InputSection instead of just the bool, which would be handy for ICF too. But I ended up not needing it for this patch, so I removed that again for now. Differential Revision: https://reviews.llvm.org/D102076 |
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.. | ||
Arch | ||
CMakeLists.txt | ||
Config.h | ||
Driver.cpp | ||
Driver.h | ||
DriverUtils.cpp | ||
Dwarf.cpp | ||
Dwarf.h | ||
ExportTrie.cpp | ||
ExportTrie.h | ||
InputFiles.cpp | ||
InputFiles.h | ||
InputSection.cpp | ||
InputSection.h | ||
LTO.cpp | ||
LTO.h | ||
MachOStructs.h | ||
MapFile.cpp | ||
MapFile.h | ||
MergedOutputSection.cpp | ||
MergedOutputSection.h | ||
ObjC.cpp | ||
ObjC.h | ||
Options.td | ||
OutputSection.cpp | ||
OutputSection.h | ||
OutputSegment.cpp | ||
OutputSegment.h | ||
Relocations.cpp | ||
Relocations.h | ||
SymbolTable.cpp | ||
SymbolTable.h | ||
Symbols.cpp | ||
Symbols.h | ||
SyntheticSections.cpp | ||
SyntheticSections.h | ||
Target.cpp | ||
Target.h | ||
UnwindInfoSection.cpp | ||
UnwindInfoSection.h | ||
Writer.cpp | ||
Writer.h |