[clang] [clang][SemaCXX] Fix crash caused by unresolved overloaded function type when using `__builtin_bit_cast` (PR #200574)

[Rajveer Singh Bharadwaj via cfe-commits]

https://github.com/Rajveer100 updated https://github.com/llvm/llvm-project/pull/200574

>From 424016df3a6101526074ba017fd103e6d1f53678 Mon Sep 17 00:00:00 2001
From: Rajveer <rajveer.developer at icloud.com>
Date: Sat, 30 May 2026 18:31:33 +0530
Subject: [PATCH] [clang][SemaCXX] Fix crash caused by unresolved overloaded
 function type when using `__builtin_bit_cast`

Resolves #200112

By early checking for placeholder expressions, crash can be avoided for
unreachable builtin type when fetching type info.
---
 clang/docs/ReleaseNotes.rst             |  2 ++
 clang/lib/Sema/SemaCast.cpp             |  7 +++++++
 clang/test/SemaCXX/builtin-bit-cast.cpp | 10 ++++++++++
 3 files changed, 19 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3c1eacfc05dc8..bceddf6e6bd9b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -619,6 +619,8 @@ Bug Fixes to Compiler Builtins
 - Fixed a crash when calling `__builtin_allow_sanitize_check` with no arguments. (#GH183927)
 - ``__annotation`` is now diagnosed as unsupported on non-Windows/UEFI targets, fixing a
   crash when using it with ``-fms-extensions`` on other platforms. (#GH184318)
+- Fixed a compiler crash due to an unresolved overloaded function type when
+  calling ``__builtin_bit_cast``. (#GH200112)
 
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 0040f3aa1a891..133837623a7a6 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -439,6 +439,13 @@ ExprResult Sema::ActOnBuiltinBitCastExpr(SourceLocation KWLoc, Declarator &D,
 ExprResult Sema::BuildBuiltinBitCastExpr(SourceLocation KWLoc,
                                          TypeSourceInfo *TSI, Expr *Operand,
                                          SourceLocation RParenLoc) {
+  if (Operand->hasPlaceholderType()) {
+    ExprResult PR = CheckPlaceholderExpr(Operand);
+    if (PR.isInvalid())
+      return ExprError();
+    Operand = PR.get();
+  }
+
   CastOperation Op(*this, TSI->getType(), Operand);
   Op.OpRange = CastOperation::OpRangeType(KWLoc, KWLoc, RParenLoc);
   TypeLoc TL = TSI->getTypeLoc();
diff --git a/clang/test/SemaCXX/builtin-bit-cast.cpp b/clang/test/SemaCXX/builtin-bit-cast.cpp
index 8717371b941b0..626065d5bdc00 100644
--- a/clang/test/SemaCXX/builtin-bit-cast.cpp
+++ b/clang/test/SemaCXX/builtin-bit-cast.cpp
@@ -46,3 +46,13 @@ extern S<int> extern_decl;
 int x = __builtin_bit_cast(int, extern_decl);
 S<char> y = __builtin_bit_cast(S<char>, 0);
 }
+
+template <class To, class From>
+// expected-note at +1{{possible target for call}}
+constexpr To bit_cast(const From &from) {
+  return __builtin_bit_cast(To, bit_cast);
+  // expected-error at -1{{reference to overloaded function could not be resolved; did you mean to call it?}}
+} // expected-note {{control reached end of constexpr function}}
+constexpr __int128_t foo = bit_cast<__int128_t>((long double)0);
+// expected-error at -1{{constexpr variable 'foo' must be initialized by a constant expression}}
+// expected-note at -2{{in call to 'bit_cast<__int128, long double>((long double)0)'}}