[PATCH] D51443: [dsymutil] Remove non-determinism.

[Jonas Devlieghere via Phabricator via llvm-commits]

JDevlieghere created this revision.
JDevlieghere added reviewers: friss, aprantl.
Herald added a subscriber: mgrang.

Before this patch, analyzeContext called `getCanonicalDIEOffset()`, for which the result depends on the timings of the `setCanonicalDIEOffset()` calls in the `cloneLambda`. This can lead to slightly different output between runs.

This patch fixes this by moving the call to `getCanonicalDIEOffset()` into the `cloneLambda`.


Repository:
  rL LLVM

https://reviews.llvm.org/D51443

Files:
  llvm/tools/dsymutil/DwarfLinker.cpp


Index: llvm/tools/dsymutil/DwarfLinker.cpp
===================================================================
--- llvm/tools/dsymutil/DwarfLinker.cpp
+++ llvm/tools/dsymutil/DwarfLinker.cpp
@@ -271,6 +271,19 @@
   Info.Prune &= (DIE.getTag() == dwarf::DW_TAG_module) ||
                 dwarf::toUnsigned(DIE.find(dwarf::DW_AT_declaration), 0);
 
+  return Info.Prune;
+}
+
+/// The canonical DIE offset is calculated when cloning a DIE. Therefore we
+/// cannot do it during analysis, but rather have to fix it up at the beginning
+/// of the clone step.
+static bool updatePruning(const DWARFDie &DIE, CompileUnit &CU) {
+  unsigned MyIdx = CU.getOrigUnit().getDIEIndex(DIE);
+  CompileUnit::DIEInfo &Info = CU.getInfo(MyIdx);
+
+  for (auto Child : DIE.children())
+    Info.Prune &= updatePruning(Child, CU);
+
   // Don't prune it if there is no definition for the DIE.
   Info.Prune &= Info.Ctxt && Info.Ctxt->getCanonicalDIEOffset();
 
@@ -2512,14 +2525,13 @@
               *CU, UnitID++, !Options.NoODR && !Options.Update, ""));
         }
       }
-      
+
       // Now build the DIE parent links that we will use during the next phase.
       for (auto &CurrentUnit : LinkContext.CompileUnits) {
         auto CUDie = CurrentUnit->getOrigUnit().getUnitDIE();
         if (!CUDie)
           continue;
-        analyzeContextInfo(CurrentUnit->getOrigUnit().getUnitDIE(), 0,
-                           *CurrentUnit, &ODRContexts.getRoot(),
+        analyzeContextInfo(CUDie, 0, *CurrentUnit, &ODRContexts.getRoot(),
                            UniquingStringPool, ODRContexts);
       }
 
@@ -2547,6 +2559,15 @@
       if (!LinkContext.ObjectFile)
         continue;
 
+      // We need to update all compile units before doing lookForDIEsToKeep as
+      // the latter can follow cross-CU links through its attributes.
+      for (auto &CurrentUnit : LinkContext.CompileUnits) {
+        auto CUDie = CurrentUnit->getOrigUnit().getUnitDIE();
+        if (!CUDie)
+          continue;
+        updatePruning(CUDie, *CurrentUnit);
+      }
+
       // Then mark all the DIEs that need to be present in the linked output
       // and collect some information about them.
       // Note that this loop can not be merged with the previous one because


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