[clang] [CIR] Inline trivial copy/move assignment at call sites (PR #198918)

[Erich Keane via cfe-commits]

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@@ -901,6 +901,36 @@ void CIRGenFunction::emitImplicitAssignmentOperatorBody(FunctionArgList &args) {
   assert(!cir::MissingFeatures::incrementProfileCounter());
   assert(!cir::MissingFeatures::runCleanupsScope());
 
+  // For a memcpy-equivalent assignment operator, copy the whole object, then
+  // fall through to emit the trailing `return *this`.
+  if (assignOp->isMemcpyEquivalentSpecialMember(getContext())) {
+    CanQualType recordTy =
+        getContext().getCanonicalTagType(assignOp->getParent());
+    LValue dest = makeNaturalAlignAddrLValue(loadCXXThis(), recordTy);
+    mlir::Value srcPtr = builder.createLoad(getLoc(assignOp->getLocation()),
+                                            getAddrOfLocalVar(args.back()));
+    LValue src = makeNaturalAlignAddrLValue(srcPtr, recordTy);
+    emitAggregateAssign(dest, src, recordTy);
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erichkeane wrote:

Hmm... this really seems wrong to me.  I think we should just leave the copies and count on some level of optimization to figure out "this is all the things, just optimize them all".

CIR should better reflect the AST/semantics.

https://github.com/llvm/llvm-project/pull/198918