[lld] r329088 - [lld] fix data race in ELF/ICF.cpp
Bob Haarman via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 3 10:27:40 PDT 2018
Author: inglorion
Date: Tue Apr 3 10:27:39 2018
New Revision: 329088
URL: http://llvm.org/viewvc/llvm-project?rev=329088&view=rev
Log:
[lld] fix data race in ELF/ICF.cpp
Summary:
r328610 fixed a data race in the COFF linker. This change makes a
similar fix to the ELF linker.
Reviewers: ruiu, pcc, rnk
Reviewed By: ruiu
Subscribers: emaste, llvm-commits, arichardson
Differential Revision: https://reviews.llvm.org/D45192
Modified:
lld/trunk/ELF/ICF.cpp
Modified: lld/trunk/ELF/ICF.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/ICF.cpp?rev=329088&r1=329087&r2=329088&view=diff
==============================================================================
--- lld/trunk/ELF/ICF.cpp (original)
+++ lld/trunk/ELF/ICF.cpp Tue Apr 3 10:27:39 2018
@@ -362,17 +362,12 @@ template <class ELFT> size_t ICF<ELFT>::
// vector. Therefore, Sections vector can be considered as contiguous
// groups of sections, grouped by the class.
//
-// This function calls Fn on every group that starts within [Begin, End).
-// Note that a group must start in that range but doesn't necessarily
-// have to end before End.
+// This function calls Fn on every group within [Begin, End).
template <class ELFT>
void ICF<ELFT>::forEachClassRange(size_t Begin, size_t End,
std::function<void(size_t, size_t)> Fn) {
- if (Begin > 0)
- Begin = findBoundary(Begin - 1, End);
-
while (Begin < End) {
- size_t Mid = findBoundary(Begin, Sections.size());
+ size_t Mid = findBoundary(Begin, End);
Fn(Begin, Mid);
Begin = Mid;
}
@@ -392,12 +387,23 @@ void ICF<ELFT>::forEachClass(std::functi
Current = Cnt % 2;
Next = (Cnt + 1) % 2;
- // Split sections into 256 shards and call Fn in parallel.
- size_t NumShards = 256;
+ // Shard into non-overlapping intervals, and call Fn in parallel.
+ // The sharding must be completed before any calls to Fn are made
+ // so that Fn can modify the Chunks in its shard without causing data
+ // races.
+ const size_t NumShards = 256;
size_t Step = Sections.size() / NumShards;
- parallelForEachN(0, NumShards, [&](size_t I) {
- size_t End = (I == NumShards - 1) ? Sections.size() : (I + 1) * Step;
- forEachClassRange(I * Step, End, Fn);
+ size_t Boundaries[NumShards + 1];
+ Boundaries[0] = 0;
+ Boundaries[NumShards] = Sections.size();
+
+ parallelForEachN(1, NumShards, [&](size_t I) {
+ Boundaries[I] = findBoundary((I - 1) * Step, Sections.size());
+ });
+
+ parallelForEachN(1, NumShards + 1, [&](size_t I) {
+ if (Boundaries[I - 1] < Boundaries[I])
+ forEachClassRange(Boundaries[I - 1], Boundaries[I], Fn);
});
++Cnt;
}
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