[PATCH] D13545: [RuntimeDyld] Fix performance problem in resolveRelocations with many sections

[Keno Fischer via llvm-commits]

loladiro created this revision.
loladiro added a reviewer: lhames.
loladiro added a subscriber: llvm-commits.
loladiro set the repository for this revision to rL LLVM.

Rather than just iterating over all sections and checking whether we have relocations for them, iterate over the relocation map instead. This showed up heavily in an artificial julia benchmark that does lots of compilation. On that particular benchmark, this patch gives
~15% performance improvements. As far as I can tell the primary reason why the original
loop was so expensive is that Relocations[i] actually constructs a relocationList (allocating memory & doing lots of other unnecessary computing) if none is found.

Repository:
  rL LLVM

http://reviews.llvm.org/D13545

Files:
  lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

Index: lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
===================================================================
--- lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
+++ lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
@@ -91,18 +91,18 @@
   // First, resolve relocations associated with external symbols.
   resolveExternalSymbols();
 
-  // Just iterate over the sections we have and resolve all the relocations
-  // in them. Gross overkill, but it gets the job done.
-  for (int i = 0, e = Sections.size(); i != e; ++i) {
+  // Iterate over all outstanding relocations
+  for (auto it = Relocations.begin(), e = Relocations.end(); it != e; ++it) {
     // The Section here (Sections[i]) refers to the section in which the
     // symbol for the relocation is located.  The SectionID in the relocation
     // entry provides the section to which the relocation will be applied.
-    uint64_t Addr = Sections[i].LoadAddress;
-    DEBUG(dbgs() << "Resolving relocations Section #" << i << "\t"
+    int Idx = it->getFirst();
+    uint64_t Addr = Sections[Idx].LoadAddress;
+    DEBUG(dbgs() << "Resolving relocations Section #" << Idx << "\t"
                  << format("%p", (uintptr_t)Addr) << "\n");
-    resolveRelocationList(Relocations[i], Addr);
-    Relocations.erase(i);
+    resolveRelocationList(it->getSecond(), Addr);
   }
+  Relocations.clear();
 
   // Print out sections after relocation.
   DEBUG(


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