[clang] Improve stack usage to increase recursive initialization depth (PR #88546)

[Vitaly Buka via cfe-commits]

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@@ -1163,12 +1136,7 @@ class Sema;
     ConversionSequenceList
     allocateConversionSequences(unsigned NumConversions) {
       ImplicitConversionSequence *Conversions =
-          slabAllocate<ImplicitConversionSequence>(NumConversions);
-
-      // Construct the new objects.
-      for (unsigned I = 0; I != NumConversions; ++I)
-        new (&Conversions[I]) ImplicitConversionSequence();
-
+          new ImplicitConversionSequence[NumConversions];
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vitalybuka wrote:

Seems unusual to keep ownership in ArrayRef.
Could we make ConversionSequenceList just a std::vector if it owns the memory?

https://github.com/llvm/llvm-project/pull/88546