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[LLD] [COFF] Fix handling of LTO comdats with nontrivial selection types after 728cc0075e 

Commit 728cc0075e made comdat symbols
from LTO objects be treated as any regular comdat symbol. This works
great for symbols that actually are IMAGE_COMDAT_SELECT_ANY, but
if the symbols have a less trivial selection type that require comparing
either the section chunk size or contents, we can't check that before
actually doing the LTO compilation.

Therefore bring back one aspect of handling from before; that comdat
resolution with a leader from an LTO symbol is essentially skipped,
like it was before 728cc0075e.

Differential Revision: https://reviews.llvm.org/D104605
This commit is contained in:
Martin Storsjö 2021-06-20 23:58:46 +03:00
parent f9b3840c3d
commit d07f43641f
2 changed files with 50 additions and 8 deletions
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22
lld/COFF/InputFiles.cpp
View File

@ -500,12 +500,15 @@ void ObjFile::handleComdatSelection(
// symbol in `Sym` should be discarded, produce a duplicate symbol
// error, etc.
SectionChunk *leaderChunk = nullptr;
COMDATType leaderSelection = IMAGE_COMDAT_SELECT_ANY;
SectionChunk *leaderChunk = leader->getChunk();
COMDATType leaderSelection = leaderChunk->selection;
assert(leader->data && "Comdat leader without SectionChunk?");
leaderChunk = leader->getChunk();
leaderSelection = leaderChunk->selection;
if (isa<BitcodeFile>(leader->file)) {
// If the leader is only a LTO symbol, we don't know e.g. its final size
// yet, so we can't do the full strict comdat selection checking yet.
selection = leaderSelection = IMAGE_COMDAT_SELECT_ANY;
}
if ((selection == IMAGE_COMDAT_SELECT_ANY &&
leaderSelection == IMAGE_COMDAT_SELECT_LARGEST) ||
@ -558,8 +561,10 @@ void ObjFile::handleComdatSelection(
if (!config->mingw) {
symtab->reportDuplicate(leader, this);
} else {
const coff_aux_section_definition *leaderDef = findSectionDef(
leaderChunk->file->getCOFFObj(), leaderChunk->getSectionNumber());
const coff_aux_section_definition *leaderDef = nullptr;
if (leaderChunk->file)
leaderDef = findSectionDef(leaderChunk->file->getCOFFObj(),
leaderChunk->getSectionNumber());
if (!leaderDef || leaderDef->Length != def->Length)
symtab->reportDuplicate(leader, this);
}
@ -1050,8 +1055,9 @@ public:
class FakeSectionChunk {
public:
FakeSectionChunk(const coff_section *section) : chunk(nullptr, section) {
// FIXME: comdats from LTO files don't know their selection; treat them
// as "any".
// Comdats from LTO files can't be fully treated as regular comdats
// at this point; we don't know what size or contents they are going to
// have, so we can't do proper checking of such aspects of them.
chunk.selection = IMAGE_COMDAT_SELECT_ANY;
}

36
lld/test/COFF/lto-comdat-samesize.ll Normal file
View File

@ -0,0 +1,36 @@
; REQUIRES: x86
; RUN: split-file %s %t.dir
; RUN: llvm-as %t.dir/other.ll -o %t.other.bc
; RUN: llc -filetype=obj -o %t.main.obj %t.dir/main.ll
; RUN: lld-link -out:%t.exe -subsystem:console %t.other.bc %t.main.obj
#--- main.ll
target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-windows-msvc19.14.0"
$comdatData = comdat samesize
@comdatData = weak_odr dso_local global i32 42, comdat
define dso_local void @mainCRTStartup() {
entry:
tail call void @other()
ret void
}
declare dso_local void @other()
#--- other.ll
target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-windows-msvc19.14.0"
$comdatData = comdat samesize
@comdatData = weak_odr dso_local global i32 42, comdat
define dso_local void @other() {
entry:
ret void
}