[llvm] [Parallel] Revert sequential task changes (PR #109084)

[Alexey Lapshin via llvm-commits]

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@@ -1647,30 +1647,44 @@ template <class ELFT> void elf::scanRelocations() {
   bool serial = !config->zCombreloc || config->emachine == EM_MIPS ||
                 config->emachine == EM_PPC64;
   parallel::TaskGroup tg;
-  for (ELFFileBase *f : ctx.objectFiles) {
-    auto fn = [f]() {
+  auto outerFn = [&]() {
+    for (ELFFileBase *f : ctx.objectFiles) {
+      auto fn = [f]() {
+        RelocationScanner scanner;
+        for (InputSectionBase *s : f->getSections()) {
+          if (s && s->kind() == SectionBase::Regular && s->isLive() &&
+              (s->flags & SHF_ALLOC) &&
+              !(s->type == SHT_ARM_EXIDX && config->emachine == EM_ARM))
+            scanner.template scanSection<ELFT>(*s);
+        }
+      };
+      if (serial)
+        fn();
+      else
+        tg.spawn(fn);
+    }
+    auto scanEH = [] {
       RelocationScanner scanner;
-      for (InputSectionBase *s : f->getSections()) {
-        if (s && s->kind() == SectionBase::Regular && s->isLive() &&
-            (s->flags & SHF_ALLOC) &&
-            !(s->type == SHT_ARM_EXIDX && config->emachine == EM_ARM))
-          scanner.template scanSection<ELFT>(*s);
+      for (Partition &part : ctx.partitions) {
+        for (EhInputSection *sec : part.ehFrame->sections)
+          scanner.template scanSection<ELFT>(*sec, /*isEH=*/true);
+        if (part.armExidx && part.armExidx->isLive())
+          for (InputSection *sec : part.armExidx->exidxSections)
+            if (sec->isLive())
+              scanner.template scanSection<ELFT>(*sec);
       }
     };
-    tg.spawn(fn, serial);
-  }
-
-  tg.spawn([] {
-    RelocationScanner scanner;
-    for (Partition &part : ctx.partitions) {
-      for (EhInputSection *sec : part.ehFrame->sections)
-        scanner.template scanSection<ELFT>(*sec, /*isEH=*/true);
-      if (part.armExidx && part.armExidx->isLive())
-        for (InputSection *sec : part.armExidx->exidxSections)
-          if (sec->isLive())
-            scanner.template scanSection<ELFT>(*sec);
-    }
-  });
+    if (serial)
+      scanEH();
+    else
+      tg.spawn(scanEH);
----------------
avl-llvm wrote:

Do we need to run scanEH(); on main thread here? If it uses threadIndex then it will receive UINT_MAX which is unwanted. On the another hand scanEH contains whole loop and then all scanSection would be done in deterministic order. It looks like we can replace whole "if(serial)" with single "tg.spawn(scanEH);" ?


https://github.com/llvm/llvm-project/pull/109084