[clang] [Clang] prevent assertion failure for instantiation-dependent expressions in vector conversions (PR #173498)

[Oleksandr T. via cfe-commits]

https://github.com/a-tarasyuk created https://github.com/llvm/llvm-project/pull/173498

Fixes #173347

---

This patch resolves an assertion failure that occurs when instantiation-dependent expressions are constant-evaluated during vector conversions.

>From c0f04c81e894914c85fbe66ca2298e4067280e74 Mon Sep 17 00:00:00 2001
From: Oleksandr Tarasiuk <oleksandr.tarasiuk at outlook.com>
Date: Wed, 24 Dec 2025 16:56:48 +0200
Subject: [PATCH] [Clang] prevent assertion failure for instantiation-dependent
 expressions in vector conversions

---
 clang/docs/ReleaseNotes.rst   | 1 +
 clang/lib/Sema/SemaExpr.cpp   | 3 ++-
 clang/test/SemaCXX/vector.cpp | 5 +++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8e2e45b8ef385..a39c98dd146c6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -614,6 +614,7 @@ Bug Fixes to C++ Support
 - Fix the result of ``__is_pointer_interconvertible_base_of`` when arguments are qualified and passed via template parameters. (#GH135273)
 - Fixed a crash when evaluating nested requirements in requires-expressions that reference invented parameters. (#GH166325)
 - Fixed a crash when standard comparison categories (e.g. ``std::partial_ordering``) are defined with incorrect static member types. (#GH170015) (#GH56571)
+- Fixed an assertion failure in vector conversions involving instantiation-dependent template expressions. (#GH173347)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 5a31b42541d99..69e5c8028f2ed 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -10276,7 +10276,8 @@ static ExprResult convertVector(Expr *E, QualType ElementType, Sema &S) {
 /// IntTy without losing precision.
 static bool canConvertIntToOtherIntTy(Sema &S, ExprResult *Int,
                                       QualType OtherIntTy) {
-  if (Int->get()->containsErrors())
+  Expr *E = Int->get();
+  if (E->containsErrors() || E->isInstantiationDependent())
     return false;
 
   QualType IntTy = Int->get()->getType().getUnqualifiedType();
diff --git a/clang/test/SemaCXX/vector.cpp b/clang/test/SemaCXX/vector.cpp
index 06195f039cd92..744017304d121 100644
--- a/clang/test/SemaCXX/vector.cpp
+++ b/clang/test/SemaCXX/vector.cpp
@@ -799,3 +799,8 @@ template <int N> using templated_v_size = int  __attribute__((vector_size(N)));
 templated_v_size<-8> templated_v_neg_size; //expected-note{{in instantiation of template type alias 'templated_v_size' requested here}}
 
 #endif
+
+namespace GH173347 {
+typedef short __attribute__((__vector_size__(8))) V;
+template <int N> V test(V x) { return (x % 5) * N; }
+}