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[BOLT][llvm] Reduce memory used by MCInst 

Summary:
BOLT creates MCInst for every instruction from the input. For large
binaries, this means we are creating tens if not hundreds of millions of
instructions. If the number of operands for average instruction is much
less than 8, we benefit from changing the type of Operands from
SmallVector<MCOperand, 8> to SmallVector<MCOperand, 2>. That seems
to be the optimal type for X86-64 on average.

The size of MCInst goes down from 176 to 80 which often reduces BOLT
memory consumption by gigabytes.

(cherry picked from FBD18218924)
This commit is contained in:
Maksim Panchenko 2019-10-28 17:40:18 -07:00
parent a3295715e4
commit ed8be23e73
1 changed files with 18 additions and 9 deletions
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27
bolt/llvm.patch
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@ -800,9 +800,18 @@ index 38c365538e3..dec295707e9 100644
/// This fragment is always inserted before an instruction, and holds that
/// instruction as context information (as well as a mask of kinds) for
diff --git a/include/llvm/MC/MCInst.h b/include/llvm/MC/MCInst.h
index db28fd0fd6d..e136a10b264 100644
index db28fd0fd6d..fbe315b4bd0 100644
--- a/include/llvm/MC/MCInst.h
+++ b/include/llvm/MC/MCInst.h
@@ -159,7 +159,7 @@ template <> struct isPodLike<MCOperand> { static const bool value = true; };
class MCInst {
unsigned Opcode = 0;
SMLoc Loc;
- SmallVector<MCOperand, 8> Operands;
+ SmallVector<MCOperand, 2> Operands;
// These flags could be used to pass some info from one target subcomponent
// to another, for example, from disassembler to asm printer. The values of
// the flags have any sense on target level only (e.g. prefixes on x86).
@@ -187,7 +187,7 @@ public:
using const_iterator = SmallVectorImpl<MCOperand>::const_iterator;
@ -998,10 +1007,11 @@ index 46504e74bc2..836fd8ddc45 100644
Expected<Elf_Shdr_Range> sections() const;
Expected<Elf_Sym_Range> symbols(const Elf_Shdr *Sec) const {
@@ -397,6 +409,34 @@ void ELFFile<ELFT>::getRelocationTypeName(uint32_t Type,
@@ -396,6 +408,34 @@ void ELFFile<ELFT>::getRelocationTypeName(uint32_t Type,
}
}
template <class ELFT>
+template <class ELFT>
+Expected<const typename ELFFile<ELFT>::Elf_Dyn *>
+ELFFile<ELFT>::dynamic_table_begin(const Elf_Phdr *Phdr) const {
+ if (!Phdr)
@ -1029,10 +1039,9 @@ index 46504e74bc2..836fd8ddc45 100644
+ return reinterpret_cast<const Elf_Dyn *>(base() + End);
+}
+
+template <class ELFT>
template <class ELFT>
Expected<const typename ELFT::Sym *>
ELFFile<ELFT>::getRelocationSymbol(const Elf_Rel *Rel,
const Elf_Shdr *SymTab) const {
diff --git a/include/llvm/Object/ELFObjectFile.h b/include/llvm/Object/ELFObjectFile.h
index 4d001039238..62837bbcaa0 100644
--- a/include/llvm/Object/ELFObjectFile.h
@ -1045,10 +1054,11 @@ index 4d001039238..62837bbcaa0 100644
relocation_iterator section_rel_begin(DataRefImpl Sec) const override;
relocation_iterator section_rel_end(DataRefImpl Sec) const override;
section_iterator getRelocatedSection(DataRefImpl Sec) const override;
@@ -717,6 +718,14 @@ bool ELFObjectFile<ELFT>::isSectionVirtual(DataRefImpl Sec) const {
@@ -716,6 +717,14 @@ bool ELFObjectFile<ELFT>::isSectionVirtual(DataRefImpl Sec) const {
return getSection(Sec)->sh_type == ELF::SHT_NOBITS;
}
template <class ELFT>
+template <class ELFT>
+bool ELFObjectFile<ELFT>::isSectionReadOnly(DataRefImpl Sec) const {
+ const Elf_Shdr *EShdr = getSection(Sec);
+ return EShdr->sh_flags & ELF::SHF_ALLOC &&
@ -1056,10 +1066,9 @@ index 4d001039238..62837bbcaa0 100644
+ EShdr->sh_type == ELF::SHT_PROGBITS;
+}
+
+template <class ELFT>
template <class ELFT>
relocation_iterator
ELFObjectFile<ELFT>::section_rel_begin(DataRefImpl Sec) const {
DataRefImpl RelData;
@@ -751,9 +760,6 @@ ELFObjectFile<ELFT>::section_rel_end(DataRefImpl Sec) const {
template <class ELFT>
section_iterator