[clang] [Clang][CodeGen] Add workaround for old glibc `__PTR_ALIGN` macro (PR #137851)

[Eli Friedman via cfe-commits]

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@@ -4820,6 +4820,15 @@ bool CodeGenFunction::isUnderlyingBasePointerConstantNull(const Expr *E) {
   const Expr *UnderlyingBaseExpr = E->IgnoreParens();
   while (auto *BaseMemberExpr = dyn_cast<MemberExpr>(UnderlyingBaseExpr))
     UnderlyingBaseExpr = BaseMemberExpr->getBase()->IgnoreParens();
+  // Workaround for old glibc's __PTR_ALIGN macro
+  // If the condition can be constant evaluated, we check the selected arm.
+  if (auto *Select = dyn_cast<ConditionalOperator>(UnderlyingBaseExpr)) {
+    if (auto *C = dyn_cast_if_present<llvm::Constant>(
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efriedma-quic wrote:

EvaluateAsBooleanCondition, to ensure this is based on the AST.  (tryEmitAbstract on a boolean is mostly the same thing these days, but not quite.)

https://github.com/llvm/llvm-project/pull/137851