[PATCH] D13618: [Extension] Optimizing const member objects.

[Richard Smith via cfe-commits]

rsmith added a subscriber: rsmith.

================
Comment at: lib/CodeGen/CGDecl.cpp:933
@@ +932,3 @@
+  ASTContext &Ctx = getContext();
+  auto &OffsetsInfo = InvariantOffsets.FindAndConstruct(Record).second;
+  OffsetsType &Args = OffsetsInfo.Offsets;
----------------
Instead of tracking a separate `Computed` flag, use `InvariantOffsets.count(Record)` here, and insert the value below.

================
Comment at: lib/CodeGen/CGDecl.cpp:943-959
@@ -950,2 +942,19 @@
+
+  // Trace through fields collecting offsets of writeonce candidates.
+  for (const auto *Field : Record->fields()) {
+    assert(dyn_cast<FieldDecl>(Field) && "Field decls only.");
+    QualType FieldType = Field->getType();
+    if (FieldType.isWriteOnce(Ctx)) {
+      CharUnits WidthChars = Ctx.getTypeSizeInChars(FieldType);
+      uint64_t Width = WidthChars.getQuantity();
+      Args.push_back(llvm::ConstantInt::get(Int64Ty, Width));  // Size
+
+      uint64_t Offset = Ctx.getFieldOffset(Field);
+      Args.push_back(llvm::ConstantInt::get(Int64Ty, Offset));  // Offset
+    } else if (const CXXRecordDecl *RecField =
+               Ctx.getBaseElementType(FieldType)->getAsCXXRecordDecl()) {
+      auto &FieldArgs = ComputeInvariantOffsets(RecField);
+      Args.insert(Args.end(), FieldArgs.begin(), FieldArgs.end());
     }
   }
+
----------------
It'd be good to also handle the case of a `const` field of class type that contains a `mutable` member -- in that case, all members other than the `mutable` member can be marked as invariant.

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Comment at: lib/CodeGen/CGDecl.cpp:956-957
@@ -950,1 +955,4 @@
+               Ctx.getBaseElementType(FieldType)->getAsCXXRecordDecl()) {
+      auto &FieldArgs = ComputeInvariantOffsets(RecField);
+      Args.insert(Args.end(), FieldArgs.begin(), FieldArgs.end());
     }
----------------
The recursive call to `ComputeInvariatOffsets` here invalidates your `Args` reference (`DenseMap` insertions invalidate all iterators and references to map elements).


http://reviews.llvm.org/D13618