[clang] [Clang] Introduce __builtin_is_modifiable_lvalue() (PR #132524)

[Andrew Pinski via cfe-commits]

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@@ -12985,6 +12985,16 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     assert(Src.isInt());
     return Success((Src.getInt() & (Alignment - 1)) == 0 ? 1 : 0, E);
   }
+  case Builtin::BI__builtin_is_modifiable_lvalue: {
+    const Expr *Arg = E->getArg(0);
+    SpeculativeEvaluationRAII SpeculativeEval(Info);
+    IgnoreSideEffectsRAII Fold(Info);
+
+    SourceLocation OrigLoc = Arg->getExprLoc();
+    bool IsLValue = Arg->IgnoreCasts()->isModifiableLvalue(
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pinskia wrote:

I suspect `IgnoreCasts()` should be removed here. Otherwise `(int)var` would be allowed. As we talked about on mastodon. The GCC implemention does not ignore casts.

https://github.com/llvm/llvm-project/pull/132524