[llvm] dd832c7 - [RuntimeDyld] Speedup resolution of relocations to external symbols

[Maksim Panchenko via llvm-commits]

Author: Maksim Panchenko
Date: 2021-03-11T16:58:49-08:00
New Revision: dd832c7d3a7c808d76207a95a97ca14b3006874d

URL: https://github.com/llvm/llvm-project/commit/dd832c7d3a7c808d76207a95a97ca14b3006874d
DIFF: https://github.com/llvm/llvm-project/commit/dd832c7d3a7c808d76207a95a97ca14b3006874d.diff

LOG: [RuntimeDyld] Speedup resolution of relocations to external symbols

>From what I can tell, the loop inside applyExternalSymbolRelocations()
used to call getSymbolAddress(). After the JITSymbolResolver interface
redesign, the functionality has changed, and the loop should no longer
trigger repopulation of ExternalSymbolRelocations. If that's the case,
there is no need to update the loop iterator manually, and
ExternalSymbolRelocations can be cleared at once. This way, when there
are many external symbols in the program, the function runs much faster.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D97531

Added: 
    

Modified: 
    llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

Removed: 
    


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diff  --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
index e49e6e541f15..cd1da2a00164 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
@@ -1085,16 +1085,13 @@ void RuntimeDyldImpl::resolveRelocationList(const RelocationList &Relocs,
 
 void RuntimeDyldImpl::applyExternalSymbolRelocations(
     const StringMap<JITEvaluatedSymbol> ExternalSymbolMap) {
-  while (!ExternalSymbolRelocations.empty()) {
-
-    StringMap<RelocationList>::iterator i = ExternalSymbolRelocations.begin();
-
-    StringRef Name = i->first();
+  for (auto &RelocKV : ExternalSymbolRelocations) {
+    StringRef Name = RelocKV.first();
+    RelocationList &Relocs = RelocKV.second;
     if (Name.size() == 0) {
       // This is an absolute symbol, use an address of zero.
       LLVM_DEBUG(dbgs() << "Resolving absolute relocations."
                         << "\n");
-      RelocationList &Relocs = i->second;
       resolveRelocationList(Relocs, 0);
     } else {
       uint64_t Addr = 0;
@@ -1105,13 +1102,6 @@ void RuntimeDyldImpl::applyExternalSymbolRelocations(
         assert(RRI != ExternalSymbolMap.end() && "No result for symbol");
         Addr = RRI->second.getAddress();
         Flags = RRI->second.getFlags();
-        // The call to getSymbolAddress may have caused additional modules to
-        // be loaded, which may have added new entries to the
-        // ExternalSymbolRelocations map.  Consquently, we need to update our
-        // iterator.  This is also why retrieval of the relocation list
-        // associated with this symbol is deferred until below this point.
-        // New entries may have been added to the relocation list.
-        i = ExternalSymbolRelocations.find(Name);
       } else {
         // We found the symbol in our global table.  It was probably in a
         // Module that we loaded previously.
@@ -1137,15 +1127,11 @@ void RuntimeDyldImpl::applyExternalSymbolRelocations(
 
         LLVM_DEBUG(dbgs() << "Resolving relocations Name: " << Name << "\t"
                           << format("0x%lx", Addr) << "\n");
-        // This list may have been updated when we called getSymbolAddress, so
-        // don't change this code to get the list earlier.
-        RelocationList &Relocs = i->second;
         resolveRelocationList(Relocs, Addr);
       }
     }
-
-    ExternalSymbolRelocations.erase(i);
   }
+  ExternalSymbolRelocations.clear();
 }
 
 Error RuntimeDyldImpl::resolveExternalSymbols() {