[llvm] [InstCombine] Extend folding of aggregate construction to cases when source aggregates are partially available (PR #100828)

[via llvm-commits]

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@@ -1117,9 +1124,68 @@ Instruction *InstCombinerImpl::foldAggregateConstructionIntoAggregateReuse(
     // aggregate produced by OrigIVI must have been originally extracted from
     // the same aggregate. Is that so? Can we find said original aggregate?
     SourceAggregate = FindCommonSourceAggregate(UseBB, Pred);
-    if (Describe(SourceAggregate) != AggregateDescription::Found)
-      return nullptr; // Give up.
-    IV.first->second = *SourceAggregate;
+    if (Describe(SourceAggregate) == AggregateDescription::Found) {
+      FoundSrcAgg = true;
+      IV.first->second = *SourceAggregate;
+    } else {
+      // If UseBB is the single successor of Pred, we can add InsertValue to
+      // Pred.
+      auto *BI = dyn_cast<BranchInst>(Pred->getTerminator());
+      if (!BI || !BI->isUnconditional())
+        return nullptr;
+    }
+  }
+
+  if (!FoundSrcAgg)
+    return nullptr;
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weiguozhi wrote:

Because we limits the insertvalue to be moved to immediate predecessors and UseBB is the only successor of PredBB, the total execution count of UseBB is the sum of all predecessors. So once we have found some source aggregate in a PredBB, add insertvalue to all other predecessors still results in less dynamic count of insertvalue instructions.

https://github.com/llvm/llvm-project/pull/100828