[clang] [clang] Implement constexpr heap allocation alignments (PR #174549)

[via cfe-commits]

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@@ -10569,6 +10663,8 @@ static CharUnits getBaseAlignment(EvalInfo &Info, const LValue &Value) {
     return Info.Ctx.getDeclAlign(VD);
   if (const auto *E = Value.Base.dyn_cast<const Expr *>())
     return GetAlignOfExpr(Info.Ctx, E, UETT_AlignOf);
+  if (const auto &DA = Value.Base.dyn_cast<DynamicAllocLValue>())
+    return Info.Ctx.toCharUnitsFromBits(DA.getAlign());
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keinflue wrote:

But the alignment guarantees aren't only dependent on the type (including dynamic array size). So that information isn't sufficient to calculate the alignment ad-hoc.

https://github.com/llvm/llvm-project/pull/174549