[clang] [CIR] Upstream CastOp and scalar conversions (PR #130690)

[Morris Hafner via cfe-commits]

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@@ -121,29 +364,173 @@ mlir::Value CIRGenFunction::emitScalarExpr(const Expr *e) {
   return ScalarExprEmitter(*this, builder).Visit(const_cast<Expr *>(e));
 }
 
+[[maybe_unused]] static bool MustVisitNullValue(const Expr *e) {
+  // If a null pointer expression's type is the C++0x nullptr_t, then
+  // it's not necessarily a simple constant and it must be evaluated
+  // for its potential side effects.
+  return e->getType()->isNullPtrType();
+}
+
 // Emit code for an explicit or implicit cast.  Implicit
 // casts have to handle a more broad range of conversions than explicit
 // casts, as they handle things like function to ptr-to-function decay
 // etc.
 mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *ce) {
-  Expr *e = ce->getSubExpr();
+  Expr *subExpr = ce->getSubExpr();
   QualType destTy = ce->getType();
   CastKind kind = ce->getCastKind();
 
+  // These cases are generally not written to ignore the result of evaluating
+  // their sub-expressions, so we clear this now.
+  ignoreResultAssign = false;
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mmha wrote:

Note that `ignoreResultAssign` is a member variable and retains its value while we visit the expression. We might get called recursively so we should keep this store.

https://github.com/llvm/llvm-project/pull/130690