[clang] [clang] Lower _BitInt(129+) to a different type in LLVM IR (PR #91364)

[John McCall via cfe-commits]

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@@ -1886,6 +1896,29 @@ llvm::Constant *ConstantEmitter::emitForMemory(CodeGenModule &CGM,
     return Res;
   }
 
+  if (destType->isBitIntType()) {
+    if (CGM.getTypes().typeRequiresSplitIntoByteArray(destType, C->getType())) {
+      // Long _BitInt has array of bytes as in-memory type.
+      // So, split constant into individual bytes.
+      ConstantAggregateBuilder Builder(CGM);
+      llvm::Type *DesiredTy = CGM.getTypes().ConvertTypeForMem(destType);
+      llvm::Type *LoadStoreTy =
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rjmccall wrote:

Right.  Momchil, your description is actually a totally reasonable way of understanding what `convertTypeForLoadStore` *means* for `_BitInt`: the load/store type is an integer type that has the same width as the in-memory type.  We're just recognizing that as a more general concept.

https://github.com/llvm/llvm-project/pull/91364