[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 +1118,35 @@ 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.
+      if (succ_size(Pred) != 1)
+        return nullptr; // Give up.
+    }
+  }
+
+  if (!FoundSrcAgg)
+    return nullptr;
+
+  // For predecessors without appropriate source aggregate, create one in the
+  // predecessor.
+  for (auto &It : SourceAggregates) {
+    if (Describe(It.second) == AggregateDescription::Found)
+      continue;
+
+    BasicBlock *Pred = It.first;
+    Builder.SetInsertPoint(Pred, Pred->getTerminator()->getIterator());
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weiguozhi wrote:

It is because I expect DoPHITranslation translates a value into another value accessible in predecessor, if a value  is defined in successor, I expect DoPHITranslation returns null, but it actually returns the value itself, it is not accessible from predecessor, so it causes the error.


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