[PATCH] D36351: [lld][ELF] Add profile guided section layout

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added a comment.

Could you send me a patch to produce a call graph file so that I can try this patch on my machine?



================
Comment at: ELF/CallGraphSort.cpp:99-101
+  if (To != Other.To)
+    return To < Other.To;
+  return false;
----------------
You can just return `To < Other.To`.


================
Comment at: ELF/CallGraphSort.cpp:127
+  // Create the graph.
+  for (const auto &C : Profile) {
+    if (C.second == 0)
----------------
This loop is a bit too dense. It cannot be understood without reading each line carefully as I don't understand the whole picture. Please insert a blank line between code blocks. Adding more comment would help.


================
Comment at: ELF/CallGraphSort.cpp:128
+  for (const auto &C : Profile) {
+    if (C.second == 0)
+      continue;
----------------
Please define local variables for `C.first.first`, `C.first.second` and `C.second` so that they are accessed through meaningful names.


================
Comment at: ELF/CallGraphSort.cpp:130-135
+    auto FromDR = dyn_cast_or_null<DefinedRegular>(Symtab->find(C.first.first));
+    auto ToDR = dyn_cast_or_null<DefinedRegular>(Symtab->find(C.first.second));
+    if (!FromDR || !ToDR)
+      continue;
+    auto FromSB = dyn_cast_or_null<const InputSectionBase>(FromDR->Section);
+    auto ToSB = dyn_cast_or_null<const InputSectionBase>(ToDR->Section);
----------------
auto -> auto *


================
Comment at: ELF/CallGraphSort.cpp:147
+      Nodes[To].IncidentEdges.push_back(EI);
+    } else
+      Edges[EI].Weight = SaturatingAdd(Edges[EI].Weight, C.second);
----------------
nit: add {}


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Comment at: ELF/CallGraphSort.cpp:153
+
+void CallGraphSort::contractEdge(EdgeIndex CEI) {
+  // Make a copy of the edge as the original will be marked killed while being
----------------
Please add a function comment as to what this function is intended to do. I do not understand this function because I don't get a whole picture.


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Comment at: ELF/CallGraphSort.cpp:158-163
+  // Remove the self edge from From.
+  FE.erase(std::remove(FE.begin(), FE.end(), CEI));
+  std::vector<EdgeIndex> &TE = Nodes[CE.To].IncidentEdges;
+  // Update all edges incident with To to reference From instead. Then if they
+  // aren't self edges add them to From.
+  for (EdgeIndex EI : TE) {
----------------
Add blank lines before comments.


================
Comment at: ELF/CallGraphSort.cpp:165-166
+    Edge &E = Edges[EI];
+    // E.From = E.From == CE.To ? CE.From : E.From;
+    // E.To = E.To == CE.To ? CE.From : E.To;
+    if (E.From == CE.To)
----------------
Please remove debug code.


================
Comment at: ELF/CallGraphSort.cpp:178-180
+  // Free memory.
+  std::vector<EdgeIndex>().swap(TE);
+
----------------
This looks odd. Why do you need to do this? I think you can just leave it alone.


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Comment at: ELF/CallGraphSort.cpp:207-208
+
+// Group InputSections into clusters using the Call-Chain Clustering heuristic
+// then sort the clusters by density.
+void CallGraphSort::generateClusters() {
----------------
This might be understood for those who read the paper, but I don't think that is enough. Please write more comment as to what are clusters, what is density, and what is the heuristic.


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Comment at: ELF/CallGraphSort.cpp:272-273
+DenseMap<const InputSectionBase *, int> elf::computeCallGraphProfileOrder() {
+  CallGraphSort CGS(Config->CallGraphProfile);
+  return CGS.run();
+}
----------------
You can do this in one line without defining a local variable.


================
Comment at: ELF/Writer.cpp:926-928
+    for (BaseCommand *Base : Script->Opt.Commands)
+      if (auto *OS = dyn_cast<OutputSection>(Base))
+        if (OS->Name == ".text") {
----------------
I'd factor this code out as `OutputSection *findOutputSection(StringRef Name)`.


https://reviews.llvm.org/D36351