[clang] [Clang] Fix assertion when instantiating a matrix type with an invalid element type (PR #224331)

[Akash Manna via cfe-commits]

https://github.com/akash-manna-sky created https://github.com/llvm/llvm-project/pull/224331

Fixes #202744

`Sema::BuildMatrixType` skips the element type check while the element type is dependent, so `template <typename Y> using matrix_5_5 = Y __attribute__((matrix_type(5, 5)));` gives a `ConstantMatrixType` whose element is still unchecked. On instantiation, `TreeTransform::RebuildConstantMatrixType` called `ASTContext::getConstantMatrixType` directly, so nothing ever validated the substituted type. `matrix_5_5<matrix_5_5<float>>` then hit the "need a valid element type" assertion. The dependent-dimension case (`matrix_type(R, C)`) was fine because `RebuildDependentSizedMatrixType` already goes through `BuildMatrixType`.

`RebuildConstantMatrixType` now goes through `Sema::BuildMatrixType` as well, the same way `RebuildExtVectorType` does for vectors: it takes the attribute location and wraps the dimensions in integer literals. An invalid instantiated element type now gets the usual `invalid matrix element type` error instead of crashing, and the `_BitInt` element check that this path also skipped is applied too.


>From 8e0410fe99bd1731d4a5b5dd058909b777707aeb Mon Sep 17 00:00:00 2001
From: Akash Manna <akash.manna.mymail at gmail.com>
Date: Thu, 17 Sep 2026 20:30:29 +0530
Subject: [PATCH] [Clang] Fix assertion when instantiating a matrix type with
 an invalid element type

A matrix_type with constant dimensions and a dependent element type is
built as a ConstantMatrixType, with the element type check deferred to
instantiation. TreeTransform::RebuildConstantMatrixType then called
ASTContext::getConstantMatrixType directly, so the check never ran and
an invalid element type (e.g. another matrix) hit the "need a valid
element type" assertion.

Rebuild the type through Sema::BuildMatrixType instead, as
RebuildDependentSizedMatrixType already does, so the instantiated
element type is validated and diagnosed like in the non-template case.

Fixes #202744
---
 clang/docs/ReleaseNotes.md              |  4 ++++
 clang/lib/Sema/TreeTransform.h          | 19 ++++++++++++++-----
 clang/test/SemaTemplate/matrix-type.cpp | 18 ++++++++++++++++++
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 3cca316a91d4d3..cec77fafe37723 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -626,6 +626,10 @@ features cannot lower the translation-unit ABI level;
 - Fixed an assertion when an invalid statement appeared in a ``switch``
   statement nested inside a C++26 expansion statement. (#GH210575)
 
+- Fixed an assertion when a ``matrix_type`` with constant dimensions and a
+  dependent element type was instantiated with an invalid element type.
+  (#GH202744)
+
 - Fixed friend declarations sometimes making non-visible default arguments
   incorrectly visible to default argument redefinition checks across modules.
 
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index c8458fda58a88e..5ee5ee4b249b1f 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -1045,7 +1045,8 @@ class TreeTransform {
 
   /// Build a new matrix type given the element type and dimensions.
   QualType RebuildConstantMatrixType(QualType ElementType, unsigned NumRows,
-                                     unsigned NumColumns);
+                                     unsigned NumColumns,
+                                     SourceLocation AttributeLoc);
 
   /// Build a new matrix type given the type and dependently-defined
   /// dimensions.
@@ -6288,7 +6289,7 @@ TreeTransform<Derived>::TransformConstantMatrixType(TypeLocBuilder &TLB,
   QualType Result = TL.getType();
   if (getDerived().AlwaysRebuild() || ElementType != T->getElementType()) {
     Result = getDerived().RebuildConstantMatrixType(
-        ElementType, T->getNumRows(), T->getNumColumns());
+        ElementType, T->getNumRows(), T->getNumColumns(), TL.getAttrNameLoc());
     if (Result.isNull())
       return QualType();
   }
@@ -18158,9 +18159,17 @@ TreeTransform<Derived>::RebuildDependentSizedExtVectorType(QualType ElementType,
 
 template <typename Derived>
 QualType TreeTransform<Derived>::RebuildConstantMatrixType(
-    QualType ElementType, unsigned NumRows, unsigned NumColumns) {
-  return SemaRef.Context.getConstantMatrixType(ElementType, NumRows,
-                                               NumColumns);
+    QualType ElementType, unsigned NumRows, unsigned NumColumns,
+    SourceLocation AttributeLoc) {
+  ASTContext &Ctx = SemaRef.Context;
+  QualType SizeTy = Ctx.getSizeType();
+  unsigned SizeWidth = Ctx.getIntWidth(SizeTy);
+  IntegerLiteral *RowExpr = IntegerLiteral::Create(
+      Ctx, llvm::APInt(SizeWidth, NumRows), SizeTy, AttributeLoc);
+  IntegerLiteral *ColumnExpr = IntegerLiteral::Create(
+      Ctx, llvm::APInt(SizeWidth, NumColumns), SizeTy, AttributeLoc);
+  return SemaRef.BuildMatrixType(ElementType, RowExpr, ColumnExpr,
+                                 AttributeLoc);
 }
 
 template <typename Derived>
diff --git a/clang/test/SemaTemplate/matrix-type.cpp b/clang/test/SemaTemplate/matrix-type.cpp
index 1843c0a1a6ed62..a2ee6fdb3e08d4 100644
--- a/clang/test/SemaTemplate/matrix-type.cpp
+++ b/clang/test/SemaTemplate/matrix-type.cpp
@@ -152,6 +152,24 @@ int test_make6() {
   make6<2, 2>::type y;
 }
 
+namespace GH202744 {
+template <typename Y>
+using matrix_5_5 = Y __attribute__((matrix_type(5, 5))); // expected-error{{invalid matrix element type 'matrix_5_5<float>'}}
+
+template <typename T>
+struct make7 {
+  typedef T __attribute__((matrix_type(3, 3))) type; // expected-error{{invalid matrix element type 's'}}
+};
+
+void CastDoubleMatrixToIntCStyle() {
+  matrix_5_5<float> f;
+  make7<int>::type m;
+  matrix_5_5<matrix_5_5<float>> d; // expected-note{{in instantiation of template type alias 'matrix_5_5' requested here}}
+  i = (matrix_5_5<int>)d; // expected-error{{use of undeclared identifier 'i'}}
+  make7<s> x; // expected-note{{in instantiation of}}
+}
+} // namespace GH202744
+
 namespace Deduction {
 template <typename T>
 struct X0;