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ELF: ICF: Include contents of referenced sections in initial partitioning hash. NFCI. 

On my machine this reduced median link time of lld-speed-test/chrome
from 2.68s to 2.41s. It also reduces link time of Chrome for Android
with a prototype compiler change that causes the compiler to create
large numbers of identical (modulo relocations) sections from >15
minutes to a few seconds.

Differential Revision: https://reviews.llvm.org/D54773

llvm-svn: 347594
This commit is contained in:
Peter Collingbourne 2018-11-26 21:15:47 +00:00
parent b955bf382c
commit c81be65166
1 changed files with 27 additions and 2 deletions
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29
lld/ELF/ICF.cpp
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@ -119,6 +119,9 @@ private:
void forEachClass(llvm::function_ref<void(size_t, size_t)> Fn);
template <class RelTy>
void combineRelocHashes(InputSection *IS, ArrayRef<RelTy> Rels);
std::vector<InputSection *> Sections;
// We repeat the main loop while `Repeat` is true.
@ -423,6 +426,22 @@ void ICF<ELFT>::forEachClass(llvm::function_ref<void(size_t, size_t)> Fn) {
++Cnt;
}
// Combine the hashes of the sections referenced by the given section into its
// hash.
template <class ELFT>
template <class RelTy>
void ICF<ELFT>::combineRelocHashes(InputSection *IS, ArrayRef<RelTy> Rels) {
uint32_t Hash = IS->Class[1];
for (RelTy Rel : Rels) {
Symbol &S = IS->template getFile<ELFT>()->getRelocTargetSym(Rel);
if (auto *D = dyn_cast<Defined>(&S))
if (auto *RelSec = dyn_cast_or_null<InputSection>(D->Section))
Hash ^= RelSec->Class[1];
}
// Set MSB to 1 to avoid collisions with non-hash IDs.
IS->Class[0] = Hash | (1U << 31);
}
static void print(const Twine &S) {
if (Config->PrintIcfSections)
message(S);
@ -438,8 +457,14 @@ template <class ELFT> void ICF<ELFT>::run() {
// Initially, we use hash values to partition sections.
parallelForEach(Sections, [&](InputSection *S) {
// Set MSB to 1 to avoid collisions with non-hash IDs.
S->Class[0] = xxHash64(S->data()) | (1U << 31);
S->Class[1] = xxHash64(S->data());
});
parallelForEach(Sections, [&](InputSection *S) {
if (S->AreRelocsRela)
combineRelocHashes(S, S->template relas<ELFT>());
else
combineRelocHashes(S, S->template rels<ELFT>());
});
// From now on, sections in Sections vector are ordered so that sections