[lld] r261327 - Add support for merging strings with alignment larger than one char.
Rafael Espindola via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 19 06:17:40 PST 2016
Author: rafael
Date: Fri Feb 19 08:17:40 2016
New Revision: 261327
URL: http://llvm.org/viewvc/llvm-project?rev=261327&view=rev
Log:
Add support for merging strings with alignment larger than one char.
This reduces the .rodata of scyladb from 4501932 to 4334639 bytes (1.038
times smaller).
I don't think it is critical to support tail merging, just exact
duplicates, but given the code organization it was actually a bit easier
to support both.
Added:
lld/trunk/test/ELF/tail-merge-string-align.s
Modified:
lld/trunk/ELF/InputFiles.cpp
lld/trunk/ELF/OutputSections.cpp
lld/trunk/ELF/OutputSections.h
lld/trunk/ELF/Writer.cpp
lld/trunk/test/ELF/merge-string-align.s
Modified: lld/trunk/ELF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputFiles.cpp?rev=261327&r1=261326&r2=261327&view=diff
==============================================================================
--- lld/trunk/ELF/InputFiles.cpp (original)
+++ lld/trunk/ELF/InputFiles.cpp Fri Feb 19 08:17:40 2016
@@ -162,15 +162,15 @@ static bool shouldMerge(const typename E
if (!EntSize || Sec.sh_size % EntSize)
fatal("SHF_MERGE section size must be a multiple of sh_entsize");
- // Don't try to merge if the aligment is larger than the sh_entsize.
+ // Don't try to merge if the aligment is larger than the sh_entsize and this
+ // is not SHF_STRINGS.
//
- // If this is not a SHF_STRINGS, we would need to pad after every entity. It
- // would be equivalent for the producer of the .o to just set a larger
+ // Since this is not a SHF_STRINGS, we would need to pad after every entity.
+ // It would be equivalent for the producer of the .o to just set a larger
// sh_entsize.
- //
- // If this is a SHF_STRINGS, the larger alignment makes sense. Unfortunately
- // it would complicate tail merging. This doesn't seem that common to
- // justify the effort.
+ if (Flags & SHF_STRINGS)
+ return true;
+
if (Sec.sh_addralign > EntSize)
return false;
Modified: lld/trunk/ELF/OutputSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=261327&r1=261326&r2=261327&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.cpp (original)
+++ lld/trunk/ELF/OutputSections.cpp Fri Feb 19 08:17:40 2016
@@ -1223,8 +1223,9 @@ template <class ELFT> void EHOutputSecti
template <class ELFT>
MergeOutputSection<ELFT>::MergeOutputSection(StringRef Name, uint32_t Type,
- uintX_t Flags)
- : OutputSectionBase<ELFT>(Name, Type, Flags) {}
+ uintX_t Flags, uintX_t Alignment)
+ : OutputSectionBase<ELFT>(Name, Type, Flags),
+ Builder(llvm::StringTableBuilder::RAW, Alignment) {}
template <class ELFT> void MergeOutputSection<ELFT>::writeTo(uint8_t *Buf) {
if (shouldTailMerge()) {
Modified: lld/trunk/ELF/OutputSections.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=261327&r1=261326&r2=261327&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.h (original)
+++ lld/trunk/ELF/OutputSections.h Fri Feb 19 08:17:40 2016
@@ -300,14 +300,15 @@ class MergeOutputSection final : public
bool shouldTailMerge() const;
public:
- MergeOutputSection(StringRef Name, uint32_t Type, uintX_t Flags);
+ MergeOutputSection(StringRef Name, uint32_t Type, uintX_t Flags,
+ uintX_t Alignment);
void addSection(InputSectionBase<ELFT> *S) override;
void writeTo(uint8_t *Buf) override;
unsigned getOffset(StringRef Val);
void finalize() override;
private:
- llvm::StringTableBuilder Builder{llvm::StringTableBuilder::RAW};
+ llvm::StringTableBuilder Builder;
};
// FDE or CIE
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=261327&r1=261326&r2=261327&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Fri Feb 19 08:17:40 2016
@@ -211,7 +211,7 @@ template <bool Is64Bits> struct SectionK
StringRef Name;
uint32_t Type;
uintX_t Flags;
- uintX_t EntSize;
+ uintX_t Alignment;
};
}
namespace llvm {
@@ -225,13 +225,13 @@ template <bool Is64Bits> struct DenseMap
0, 0};
}
static unsigned getHashValue(const SectionKey<Is64Bits> &Val) {
- return hash_combine(Val.Name, Val.Type, Val.Flags, Val.EntSize);
+ return hash_combine(Val.Name, Val.Type, Val.Flags, Val.Alignment);
}
static bool isEqual(const SectionKey<Is64Bits> &LHS,
const SectionKey<Is64Bits> &RHS) {
return DenseMapInfo<StringRef>::isEqual(LHS.Name, RHS.Name) &&
LHS.Type == RHS.Type && LHS.Flags == RHS.Flags &&
- LHS.EntSize == RHS.EntSize;
+ LHS.Alignment == RHS.Alignment;
}
};
}
@@ -840,7 +840,8 @@ OutputSectionFactory<ELFT>::create(Input
Sec = new EHOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
break;
case InputSectionBase<ELFT>::Merge:
- Sec = new MergeOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags);
+ Sec = new MergeOutputSection<ELFT>(Key.Name, Key.Type, Key.Flags,
+ Key.Alignment);
break;
case InputSectionBase<ELFT>::MipsReginfo:
Sec = new MipsReginfoOutputSection<ELFT>();
@@ -863,10 +864,15 @@ OutputSectionFactory<ELFT>::createKey(In
const Elf_Shdr *H = C->getSectionHdr();
uintX_t Flags = H->sh_flags & ~SHF_GROUP;
- // For SHF_MERGE we create different output sections for each sh_entsize.
- // This makes each output section simple and keeps a single level
- // mapping from input to output.
- uintX_t EntSize = isa<MergeInputSection<ELFT>>(C) ? H->sh_entsize : 0;
+ // For SHF_MERGE we create different output sections for each alignment.
+ // This makes each output section simple and keeps a single level mapping from
+ // input to output.
+ uintX_t Alignment = 0;
+ if (isa<MergeInputSection<ELFT>>(C)) {
+ Alignment = H->sh_addralign;
+ if (H->sh_entsize > Alignment)
+ Alignment = H->sh_entsize;
+ }
// GNU as can give .eh_frame secion type SHT_PROGBITS or SHT_X86_64_UNWIND
// depending on the construct. We want to canonicalize it so that
@@ -876,7 +882,7 @@ OutputSectionFactory<ELFT>::createKey(In
isa<EHInputSection<ELFT>>(C))
Type = SHT_X86_64_UNWIND;
- return SectionKey<ELFT::Is64Bits>{OutsecName, Type, Flags, EntSize};
+ return SectionKey<ELFT::Is64Bits>{OutsecName, Type, Flags, Alignment};
}
// The linker is expected to define some symbols depending on
Modified: lld/trunk/test/ELF/merge-string-align.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/merge-string-align.s?rev=261327&r1=261326&r2=261327&view=diff
==============================================================================
--- lld/trunk/test/ELF/merge-string-align.s (original)
+++ lld/trunk/test/ELF/merge-string-align.s Fri Feb 19 08:17:40 2016
@@ -1,15 +1,20 @@
// REQUIRES: x86
// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
// RUN: ld.lld %t.o -o %t.so -shared
-// RUN: llvm-readobj -s %t.so | FileCheck %s
+// RUN: llvm-readobj -s -section-data %t.so | FileCheck %s
- .section .rodata.str1.16,"aMS", at progbits,1
+ .section .rodata.foo,"aMS", at progbits,1
.align 16
.asciz "foo"
- .section .rodata.str1.1,"aMS", at progbits,1
+ .section .rodata.foo2,"aMS", at progbits,1
+ .align 16
.asciz "foo"
+ .section .rodata.bar,"aMS", at progbits,1
+ .align 16
+ .asciz "bar"
+
// CHECK: Name: .rodata
// CHECK-NEXT: Type: SHT_PROGBITS
// CHECK-NEXT: Flags [
@@ -19,10 +24,18 @@
// CHECK-NEXT: ]
// CHECK-NEXT: Address:
// CHECK-NEXT: Offset:
-// CHECK-NEXT: Size: 4
+// CHECK-NEXT: Size: 20
// CHECK-NEXT: Link: 0
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 16
+// CHECK-NEXT: EntrySize:
+// CHECK-NEXT: SectionData (
+// CHECK-NEXT: 0000: 666F6F00 00000000 00000000 00000000 |foo.............|
+// CHECK-NEXT: 0010: 62617200 |bar.|
+// CHECK-NEXT: )
+
+ .section .rodata.str1.1,"aMS", at progbits,1
+ .asciz "foo"
// CHECK: Name: .rodata
// CHECK-NEXT: Type: SHT_PROGBITS
@@ -37,3 +50,7 @@
// CHECK-NEXT: Link: 0
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 1
+// CHECK-NEXT: EntrySize:
+// CHECK-NEXT: SectionData (
+// CHECK-NEXT: 0000: 666F6F00 |foo.|
+// CHECK-NEXT: )
Added: lld/trunk/test/ELF/tail-merge-string-align.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/tail-merge-string-align.s?rev=261327&view=auto
==============================================================================
--- lld/trunk/test/ELF/tail-merge-string-align.s (added)
+++ lld/trunk/test/ELF/tail-merge-string-align.s Fri Feb 19 08:17:40 2016
@@ -0,0 +1,35 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared -O3
+// RUN: llvm-readobj -s -section-data %t.so | FileCheck %s
+
+ .section .rodata.4a,"aMS", at progbits,1
+ .align 4
+ .asciz "abcdef"
+
+ .section .rodata.4b,"aMS", at progbits,1
+ .align 4
+ .asciz "ef"
+
+ .section .rodata.4c,"aMS", at progbits,1
+ .align 4
+ .asciz "f"
+
+
+// CHECK: Name: .rodata
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT: SHF_ALLOC
+// CHECK-NEXT: SHF_MERGE
+// CHECK-NEXT: SHF_STRINGS
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address:
+// CHECK-NEXT: Offset:
+// CHECK-NEXT: Size: 1
+// CHECK-NEXT: Link: 0
+// CHECK-NEXT: Info: 0
+// CHECK-NEXT: AddressAlignment: 4
+// CHECK-NEXT: EntrySize:
+// CHECK-NEXT: SectionData (
+// CHECK-NEXT: 0000: 61626364 65660000 6600 |abcdef..f.|
+// CHECK-NEXT: )
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