[PATCH] D156603: [SymbolSize] Improve the performance of SymbolSize computation

[Steven Wu via Phabricator via llvm-commits]

steven_wu created this revision.
steven_wu added reviewers: kubamracek, aprantl, pete.
Herald added subscribers: ributzka, hiraditya.
Herald added a project: All.
steven_wu requested review of this revision.
Herald added a project: LLVM.

The current algorithm to compute the symbol size is quadratic if there
are lots of symbols sharing the same addresses. This happens in a debug
build when lots of debug symbols get emitted in the symtab.

This patch improves the performance like `llvm-symbolizer` that replies
on the symbol size computation. Symbolizing a release+assert clang with
DebugInfo sees significant improvements from 3:40min to less than 1s.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D156603

Files:
  llvm/lib/Object/SymbolSize.cpp


Index: llvm/lib/Object/SymbolSize.cpp
===================================================================
--- llvm/lib/Object/SymbolSize.cpp
+++ llvm/lib/Object/SymbolSize.cpp
@@ -84,16 +84,21 @@
 
   array_pod_sort(Addresses.begin(), Addresses.end(), compareAddress);
 
-  // Compute the size as the gap to the next symbol
-  for (unsigned I = 0, N = Addresses.size() - 1; I < N; ++I) {
+  // Compute the size as the gap to the next symbol. If multiple symbols have
+  // the same address, give both the same size. Because Addresses is sorted,
+  // using two pointers to keep track of the current symbol vs. the next symbol
+  // that doesn't have the same address for size computation.
+  for (unsigned I = 0, NextI = 0, N = Addresses.size() - 1; I < N; ++I) {
     auto &P = Addresses[I];
     if (P.I == O.symbol_end())
       continue;
 
-    // If multiple symbol have the same address, give both the same size.
-    unsigned NextI = I + 1;
-    while (NextI < N && Addresses[NextI].Address == P.Address)
-      ++NextI;
+    // If the next pointer is behind, update it to the next symbol.
+    if (NextI <= I) {
+      NextI = I + 1;
+      while (NextI < N && Addresses[NextI].Address == P.Address)
+        ++NextI;
+    }
 
     uint64_t Size = Addresses[NextI].Address - P.Address;
     P.Address = Size;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D156603.545386.patch
Type: text/x-patch
Size: 1317 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230729/983b781b/attachment.bin>