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[LLD] [COFF] Handle undefined weak symbols in LTO #70430

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Merged
merged 1 commit into from
Nov 5, 2023
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[LLD] [COFF] Handle undefined weak symbols in LTO #70430

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2 changes: 2 additions & 0 deletions lld/COFF/InputFiles.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1040,6 +1040,8 @@ void BitcodeFile::parse() {
fakeSC = &ctx.ltoDataSectionChunk.chunk;
if (objSym.isUndefined()) {
sym = ctx.symtab.addUndefined(symName, this, false);
if (objSym.isWeak())
sym->deferUndefined = true;
} else if (objSym.isCommon()) {
sym = ctx.symtab.addCommon(this, symName, objSym.getCommonSize());
} else if (objSym.isWeak() && objSym.isIndirect()) {
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40 changes: 40 additions & 0 deletions lld/test/COFF/lto-weak-undefined.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,40 @@
; REQUIRES: x86

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Add a file-level comment about the purpose as this may be less intuitive.

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Thanks, I added this now.

;; Test linking of weak symbols with LTO. The weak symbol may be defined
;; by another object file, or may be left undefined. When compiling the
;; IR with an undefined weak symbol, the emitted object file will contain
;; a weak alias pointing at an absolute symbol for the address null.
;; Make sure both cases can be linked correctly.

; RUN: split-file %s %t.dir
; RUN: llvm-as %t.dir/main.ll -o %t.main.obj
; RUN: llvm-as %t.dir/optional.ll -o %t.optional.obj

; RUN: lld-link /entry:main %t.main.obj /out:%t-undef.exe
; RUN: lld-link /entry:main %t.main.obj %t.optional.obj /out:%t-def.exe

;--- 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-pc-windows-msvc"

define dso_local i32 @main() {
entry:
br i1 icmp ne (ptr @optionalFunc, ptr null), label %if.then, label %if.end

if.then:
tail call void @optionalFunc()
br label %if.end

if.end:
ret i32 0
}

declare extern_weak void @optionalFunc()

;--- optional.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-pc-windows-msvc"

define void @optionalFunc() {
ret void
}