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Simplify RelrSection<ELFT>::updateAllocSize. 

This patch also speeds it up by making some constants compile-time
constants. Other than that, NFC.

Differential Revision: https://reviews.llvm.org/D49101

llvm-svn: 336614
This commit is contained in:
Rui Ueyama 2018-07-09 22:29:57 +00:00
parent 77eeac3d9e
commit 703c872a4a
1 changed files with 32 additions and 38 deletions
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70
lld/ELF/SyntheticSections.cpp
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@ -1745,53 +1745,47 @@ template <class ELFT> bool RelrSection<ELFT>::updateAllocSize() {
size_t OldSize = RelrRelocs.size();
RelrRelocs.clear();
// Same as Config->Wordsize but faster because this is a compile-time
// constant.
const size_t Wordsize = sizeof(typename ELFT::uint);
// Number of bits to use for the relocation offsets bitmap.
// These many relative relocations can be encoded in a single entry.
const size_t NBits = 8 * Config->Wordsize - 1;
// Must be either 63 or 31.
const size_t NBits = Wordsize * 8 - 1;
// Get offsets for all relative relocations and sort them.
std::vector<uint64_t> Offsets;
for (const RelativeReloc &Rel : Relocs) {
for (const RelativeReloc &Rel : Relocs)
Offsets.push_back(Rel.getOffset());
}
std::sort(Offsets.begin(), Offsets.end());
llvm::sort(Offsets.begin(), Offsets.end());
uint64_t Base = 0;
typename std::vector<uint64_t>::iterator Curr = Offsets.begin();
while (Curr != Offsets.end()) {
uint64_t Current = *Curr;
assert(Current % 2 == 0);
// For each leading relocation, find following ones that can be folded
// as a bitmap and fold them.
for (size_t I = 0, E = Offsets.size(); I < E;) {
// Add a leading relocation.
RelrRelocs.push_back(Elf_Relr(Offsets[I]));
++I;
uint64_t Bits = 0;
typename std::vector<uint64_t>::iterator Next = Curr;
if (Base > 0 && Base <= Current) {
while (Next != Offsets.end()) {
uint64_t Delta = *Next - Base;
// If Next is too far out, it cannot be folded into Curr.
if (Delta >= NBits * Config->Wordsize)
break;
// If Next is not a multiple of wordsize away, it cannot
// be folded into Curr.
if (Delta % Config->Wordsize != 0)
break;
// Next can be folded into Curr, add it to the bitmap.
Bits |= 1ULL << (Delta / Config->Wordsize);
++Next;
}
// Find foldable relocations to create a bitmap.
uint64_t Bitmap = 0;
for (size_t J = I; J < E; ++J) {
uint64_t Delta = Offsets[J] - Offsets[I];
// If it is too far, it cannot be folded.
if (Delta >= NBits * Wordsize)
break;
// If it is not a multiple of wordsize away, it cannot be folded.
if (Delta % Wordsize)
break;
// Fold it.
Bitmap |= 1ULL << (Delta / Wordsize);
}
if (Bits == 0) {
RelrRelocs.push_back(Elf_Relr(Current));
// This is not a continuation entry, only one offset was
// consumed. Set base offset for subsequent bitmap entries.
Base = Current + Config->Wordsize;
++Curr;
} else {
RelrRelocs.push_back(Elf_Relr((Bits << 1) | 1));
// This is a continuation entry encoding multiple offsets
// in a bitmap. Advance base offset by NBits words.
Base += NBits * Config->Wordsize;
Curr = Next;
if (Bitmap) {
RelrRelocs.push_back(Elf_Relr((Bitmap << 1) | 1));
I += NBits;
}
}