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COFF: Allow ICF on vtable sections.

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Differential Revision: https://reviews.llvm.org/D46734

llvm-svn: 332059
This commit is contained in:
Peter Collingbourne 2018-05-10 23:31:58 +00:00
parent 0c2f6be662
commit b6c5a3045b
2 changed files with 38 additions and 5 deletions
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15
lld/COFF/ICF.cpp
View file

@ -77,9 +77,10 @@ uint32_t ICF::getHash(SectionChunk *C) {
// 2017) says that /opt:icf folds both functions and read-only data.
// Despite that, the MSVC linker folds only functions. We found
// a few instances of programs that are not safe for data merging.
// Therefore, we merge only functions just like the MSVC tool. However, we merge
// identical .xdata sections, because the address of unwind information is
// insignificant to the user program and the Visual C++ linker does this.
// Therefore, we merge only functions just like the MSVC tool. However, we also
// merge read-only sections in a couple of cases where the address of the
// section is insignificant to the user program and the behaviour matches that
// of the Visual C++ linker.
bool ICF::isEligible(SectionChunk *C) {
// Non-comdat chunks, dead chunks, and writable chunks are not elegible.
bool Writable = C->getOutputCharacteristics() & llvm::COFF::IMAGE_SCN_MEM_WRITE;
@ -90,8 +91,12 @@ bool ICF::isEligible(SectionChunk *C) {
if (C->getOutputCharacteristics() & llvm::COFF::IMAGE_SCN_MEM_EXECUTE)
return true;
// .xdata unwind info sections are eligble.
return C->getSectionName().split('$').first == ".xdata";
// .xdata unwind info sections are eligible.
if (C->getSectionName().split('$').first == ".xdata")
return true;
// So are vtables.
return C->Sym && C->Sym->getName().startswith("??_7");
}
// Split an equivalence class into smaller classes.

28
lld/test/COFF/icf-vtables.s Normal file
View file

@ -0,0 +1,28 @@
# REQUIRES: x86
# RUN: llvm-mc -triple=x86_64-windows-msvc -filetype=obj -o %t.obj %s
# RUN: lld-link %t.obj /out:%t.exe /entry:main /subsystem:console
# RUN: llvm-objdump -s %t.exe | FileCheck %s
# CHECK: Contents of section .text:
.globl main
main:
# CHECK-NEXT: 140001000 00200040 01000000 01200040 01000000
.8byte "??_"
.8byte "??_7"
# CHECK-NEXT: 140001010 01200040 01000000
.8byte "??_7a"
.section .rdata,"dr",discard,"??_"
.globl "??_"
"??_":
.byte 42
.section .rdata,"dr",discard,"??_7"
.globl "??_7"
"??_7":
.byte 42
.section .rdata,"dr",discard,"??_7a"
.globl "??_7a"
"??_7a":
.byte 42