[clang] [CIR] Add initial support for bitfields in structs (PR #142041)

[Andy Kaylor via cfe-commits]

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@@ -172,6 +195,32 @@ CIRRecordLowering::CIRRecordLowering(CIRGenTypes &cirGenTypes,
       zeroInitializable(true), zeroInitializableAsBase(true), packed(packed),
       padded(false) {}
 
+void CIRRecordLowering::setBitFieldInfo(const FieldDecl *fd,
+                                        CharUnits startOffset,
+                                        mlir::Type storageType) {
+  CIRGenBitFieldInfo &info = bitFields[fd->getCanonicalDecl()];
+  info.isSigned = fd->getType()->isSignedIntegerOrEnumerationType();
+  info.offset =
+      (unsigned)(getFieldBitOffset(fd) - astContext.toBits(startOffset));
+  info.size = fd->getBitWidthValue();
+  info.storageSize = getSizeInBits(storageType).getQuantity();
+  info.storageOffset = startOffset;
+  info.storageType = storageType;
+  info.name = fd->getName();
+
+  if (info.size > info.storageSize)
+    info.size = info.storageSize;
+  // Reverse the bit offsets for big endian machines. Because we represent
+  // a bitfield as a single large integer load, we can imagine the bits
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andykaylor wrote:

"Because we represent a bitfield as a single large integer load..."

Do we though?

https://github.com/llvm/llvm-project/pull/142041