Add a shared multi-file background writer with lazy worker startup.
Represent PDB output as a file artifact, keep PDB output state internal
to the builder, and overlap deferred PDB writers with the file maps release.
Cache immutable section and relocation metadata before color refinement,
then reuse generated-tagged concurrent tables.
Parallelize grouping and fold marking.
Include associative COMDAT descendants in contribution hashes and
canonicalize relocation targets to selected COMDAT leaders.
Stop treating COMDAT section-definition symbols as symlink anchors.
Keep zero-sized COMDAT sections only when they have an owned symlink,
so referenced empty COMDAT symbols still resolve while marker sections
like .gsspr/.gssep are skipped.
Update COMDAT/ICF tests to cover zero-sized COMDAT relocation behavior
and the adjusted removed-COMDAT handling.
Include the null import descriptor in the import directory size and derive
the IAT directory RVA from the first import descriptor of the start of
the .idata contribution.
Collapse COMDAT leader symbol patching to a single raw-symbol write path
and make the same-object versus cross-object symlink handling explicit.
Preserve public symbol offsets for ICF folds while avoiding cross-object
section number rewrites.
Fold section definition and contributions collection into a worker-count
task with barriers around the serial merge. Share section filtering
between both phases and keep zero-size COMDATs so offset-zero symbols
still map to a section.
Parse /DEF, /GUARD, and /SECTION switches, including DEF
handling for NAME/LIBRARY, BASE, VERSION, HEAPSIZE, STACKSIZE, EXPORTS,
and SECTIONS.
Store section directives in linker config and apply them consistently
when gathering object sections when pushing/searching image sections.
Pull load-config symbols for /GUARD without setting GUARD_CF until guard
tables are emitted.
Add coverage for DEF file parity, section directives, and guard
load-config handling.
Previously, COMDAT symlinks were assigned as each object batch was loaded.
Weak symbol replacement could later change the selected leader, leaving
objects from earlier passes with stale COMDAT leader refs. Library search
does not need symlinks to be valid, so solve this by doing a single sweep
assignment of COMDAT leaders after a fixed point is found.
Add identical COMDAT folding using a color-refinement over foldable
read-only sections. Hash section contents, relocation targets, and target
colors until partitions stabilize, then redirect folded COMDAT symlinks
and discard duplicate sections.
Honor .llvm_addrsig via /LLVM_ADDRSIG so address-significant sections
are not folded, keep separate color space for code, unwind info, and
MSVC vftables, and update COMDAT symbol/section mapping after folding.
Add linker tests covering function folding, relocation-sensitive folds,
alignment, color-space separation, symlink chains, .llvm_addrsig,
pdata/xdata, and C++ ICF cases.
Nikita SmithandRyan Fleury
Martins MozeikoandRyan Fleury