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COFF: ICF a section and its associated sections as a unit.

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This is needed to avoid merging two functions with identical
instructions but different xdata. It also reduces binary size by
deduplicating identical pdata sections.

Fixes PR35337.

Differential Revision: https://reviews.llvm.org/D46672

llvm-svn: 332169
This commit is contained in:
Peter Collingbourne 2018-05-12 02:12:40 +00:00
parent a41660df7e
commit 107f55005b
2 changed files with 120 additions and 4 deletions
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27
lld/COFF/ICF.cpp
View File

@ -45,6 +45,8 @@ public:
private:
void segregate(size_t Begin, size_t End, bool Constant);
bool assocEquals(const SectionChunk *A, const SectionChunk *B);
bool equalsConstant(const SectionChunk *A, const SectionChunk *B);
bool equalsVariable(const SectionChunk *A, const SectionChunk *B);
@ -91,8 +93,9 @@ bool ICF::isEligible(SectionChunk *C) {
if (C->getOutputCharacteristics() & llvm::COFF::IMAGE_SCN_MEM_EXECUTE)
return true;
// .xdata unwind info sections are eligible.
if (C->getSectionName().split('$').first == ".xdata")
// .pdata and .xdata unwind info sections are eligible.
StringRef OutSecName = C->getSectionName().split('$').first;
if (OutSecName == ".pdata" || OutSecName == ".xdata")
return true;
// So are vtables.
@ -125,6 +128,19 @@ void ICF::segregate(size_t Begin, size_t End, bool Constant) {
}
}
// Returns true if two sections' associative children are equal.
bool ICF::assocEquals(const SectionChunk *A, const SectionChunk *B) {
auto ChildClasses = [&](const SectionChunk *SC) {
std::vector<uint32_t> Classes;
for (const SectionChunk *C : SC->children())
if (!C->SectionName.startswith(".debug") &&
C->SectionName != ".gfids$y" && C->SectionName != ".gljmp$y")
Classes.push_back(C->Class[Cnt % 2]);
return Classes;
};
return ChildClasses(A) == ChildClasses(B);
}
// Compare "non-moving" part of two sections, namely everything
// except relocation targets.
bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
@ -154,7 +170,8 @@ bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
return A->getOutputCharacteristics() == B->getOutputCharacteristics() &&
A->SectionName == B->SectionName && A->Alignment == B->Alignment &&
A->Header->SizeOfRawData == B->Header->SizeOfRawData &&
A->Checksum == B->Checksum && A->getContents() == B->getContents();
A->Checksum == B->Checksum && A->getContents() == B->getContents() &&
assocEquals(A, B);
}
// Compare "moving" part of two sections, namely relocation targets.
@ -170,7 +187,9 @@ bool ICF::equalsVariable(const SectionChunk *A, const SectionChunk *B) {
return D1->getChunk()->Class[Cnt % 2] == D2->getChunk()->Class[Cnt % 2];
return false;
};
return std::equal(A->Relocs.begin(), A->Relocs.end(), B->Relocs.begin(), Eq);
return std::equal(A->Relocs.begin(), A->Relocs.end(), B->Relocs.begin(),
Eq) &&
assocEquals(A, B);
}
// Find the first Chunk after Begin that has a different class from Begin.

97
lld/test/COFF/icf-pdata.s Normal file
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@ -0,0 +1,97 @@
# RUN: llvm-mc %s -triple x86_64-windows-msvc -filetype=obj -o %t.obj
# RUN: lld-link %t.obj -dll -noentry -out:%t.dll -merge:.xdata=.xdata
# RUN: llvm-readobj -sections -coff-exports %t.dll | FileCheck %s
# CHECK: Name: .pdata
# CHECK-NEXT: VirtualSize: 0x18
# CHECK: Name: .xdata
# CHECK-NEXT: VirtualSize: 0x10
# CHECK: Name: xdata1
# CHECK-NEXT: RVA: 0x1010
# CHECK: Name: xdata1a
# CHECK-NEXT: RVA: 0x1010
# CHECK: Name: xdata1b
# CHECK-NEXT: RVA: 0x1030
.text
callee:
ret
.def xdata1;
.scl 2;
.type 32;
.endef
.section .text,"xr",one_only,xdata1
.globl xdata1 # -- Begin function xdata1
.p2align 4, 0x90
xdata1: # @xdata1
.seh_proc xdata1
# BB#0: # %entry
subq $40, %rsp
.seh_stackalloc 40
.seh_endprologue
callq callee
nop
addq $40, %rsp
jmp callee # TAILCALL
.seh_handlerdata
.section .text,"xr",one_only,xdata1
.seh_endproc
# -- End function
# xdata1a is identical to xdata1, so it should be ICFd, and so should its pdata.
# It also has associative debug and CFG sections which should be ignored by ICF.
.def xdata1a;
.scl 2;
.type 32;
.endef
.section .text,"xr",one_only,xdata1a
.globl xdata1a # -- Begin function xdata1a
.p2align 4, 0x90
xdata1a: # @xdata1a
.seh_proc xdata1a
# BB#0: # %entry
subq $40, %rsp
.seh_stackalloc 40
.seh_endprologue
callq callee
nop
addq $40, %rsp
jmp callee # TAILCALL
.seh_handlerdata
.section .text,"xr",one_only,xdata1a
.seh_endproc
.section .debug$S,"r",associative,xdata1a
.section .gfids$y,"r",associative,xdata1a
.section .gljmp$y,"r",associative,xdata1a
# xdata1b's text is identical to xdata1, but its xdata specifies a different
# stack size, so it cannot be ICFd with xdata1.
.def xdata1b;
.scl 2;
.type 32;
.endef
.section .text,"xr",one_only,xdata1b
.globl xdata1b # -- Begin function xdata1b
.p2align 4, 0x90
xdata1b: # @xdata1b
.seh_proc xdata1b
# BB#0: # %entry
subq $40, %rsp
.seh_stackalloc 48
.seh_endprologue
callq callee
nop
addq $40, %rsp
jmp callee # TAILCALL
.seh_handlerdata
.section .text,"xr",one_only,xdata1b
.seh_endproc
# -- End function
.section .drectve,"yn"
.ascii " -export:xdata1"
.ascii " -export:xdata1a"
.ascii " -export:xdata1b"