[clang] [CIR] Upstream support for operator assign (PR #145979)

[Andy Kaylor via cfe-commits]

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@@ -258,6 +258,30 @@ void CIRGenFunction::emitDelegateCXXConstructorCall(
                          /*Delegating=*/true, thisAddr, delegateArgs, loc);
 }
 
+void CIRGenFunction::emitImplicitAssignmentOperatorBody(FunctionArgList &args) {
+  const auto *assignOp = cast<CXXMethodDecl>(curGD.getDecl());
+  const Stmt *rootS = assignOp->getBody();
+  assert(isa<CompoundStmt>(rootS) &&
+         "Body of an implicit assignment operator should be compound stmt.");
+  const auto *rootCS = cast<CompoundStmt>(rootS);
+
+  // LexicalScope Scope(*this, RootCS->getSourceRange());
+  // FIXME(cir): add all of the below under a new scope.
+
+  assert(!cir::MissingFeatures::incrementProfileCounter());
+  // Classic codegen uses a special class to attempt to replace member
+  // initializers with memcpy. We could possibly defer that to the
+  // lowering or optimization phases to keep the memory accesses more
+  // explicit. For now, we don't insert memcpy at all, though in some
+  // cases the AST contains a call to memcpy.
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andykaylor wrote:

I'm not even convinced clang is always doing things like this because they couldn't be done in LLVM IR. I think sometimes it just seemed like a good idea at the time. For example, here if we just emitted a loop with calls to a B copy assignment operator that copied the single data member, the optimizer would inline the calls and turn it into a memcpy (https://godbolt.org/z/Yj4M4doYv).

https://github.com/llvm/llvm-project/pull/145979