[ELF] - Implemented --symbol-ordering-file option.
Patch allows to pass a symbols file to linker.
LLD will map symbols to sections and sort sections
in output according to symbol ordering file.
That can help to reduce the startup time and/or
amount of pagefaults during startup.
Also, interesting benchmark result was produced by Rafael Espíndola.
After applying the symbols file for clang he timed compiling
X86MCTargetDesc.ii to an object file.
The page faults went from just
56,988 to 56,946 since most faults are not in the binary.
Running time went from 4.403053515 to 4.178112244.
The speedup seems to be because of better cache
locality.
Differential revision: https://reviews.llvm.org/D26130
llvm-svn: 286440
diff --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
index 4df316e..5e7050f 100644
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -14,6 +14,7 @@
#include "LinkerScript.h"
#include "Memory.h"
#include "Strings.h"
+#include "SymbolListFile.h"
#include "SymbolTable.h"
#include "SyntheticSections.h"
#include "Target.h"
@@ -978,6 +979,21 @@
this->Size = Off;
}
+template <class ELFT>
+void OutputSection<ELFT>::sort(
+ std::function<unsigned(InputSection<ELFT> *S)> Order) {
+ typedef std::pair<unsigned, InputSection<ELFT> *> Pair;
+ auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
+
+ std::vector<Pair> V;
+ for (InputSection<ELFT> *S : Sections)
+ V.push_back({Order(S), S});
+ std::stable_sort(V.begin(), V.end(), Comp);
+ Sections.clear();
+ for (Pair &P : V)
+ Sections.push_back(P.second);
+}
+
// Sorts input sections by section name suffixes, so that .foo.N comes
// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
// We want to keep the original order if the priorities are the same
@@ -986,16 +1002,7 @@
// For more detail, read the section of the GCC's manual about init_priority.
template <class ELFT> void OutputSection<ELFT>::sortInitFini() {
// Sort sections by priority.
- typedef std::pair<int, InputSection<ELFT> *> Pair;
- auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
-
- std::vector<Pair> V;
- for (InputSection<ELFT> *S : Sections)
- V.push_back({getPriority(S->Name), S});
- std::stable_sort(V.begin(), V.end(), Comp);
- Sections.clear();
- for (Pair &P : V)
- Sections.push_back(P.second);
+ sort([](InputSection<ELFT> *S) { return getPriority(S->Name); });
}
// Returns true if S matches /Filename.?\.o$/.