[PATCH] D36562: [Bitfield] Make the bitfield a separate location if it has width of legal integer type and its bit offset is naturally aligned for the type

[Hal Finkel via Phabricator via llvm-commits]

hfinkel added inline comments.


================
Comment at: lib/CodeGen/CGRecordLayoutBuilder.cpp:411
+  // component so as it can be accessed directly with lower cost.
+  auto betterBeSingleFieldRun = [&](RecordDecl::field_iterator Field) {
+    if (!Types.getCodeGenOpts().FineGrainedBitfieldAccesses)
----------------
betterBeSingleFieldRun -> IsBetterAsSingleFieldRun


================
Comment at: lib/CodeGen/CGRecordLayoutBuilder.cpp:444
     // Add bitfields to the run as long as they qualify.
-    if (Field != FieldEnd && Field->getBitWidthValue(Context) != 0 &&
-        Tail == getFieldBitOffset(*Field)) {
-      Tail += Field->getBitWidthValue(Context);
-      ++Field;
-      continue;
+    if (Field != FieldEnd && !SingleFieldRun) {
+      SingleFieldRun = betterBeSingleFieldRun(Field);
----------------
The logic here is not obvious. Can you please add a comment. SingleFieldRun here is only not equal to `betterBeSingleFieldRun(Field)` if we've skipped 0-length bitfields, right? Please explain what's going on and also please make sure there's a test case.


Repository:
  rL LLVM

https://reviews.llvm.org/D36562