https://github.com/farzonl updated 
https://github.com/llvm/llvm-project/pull/171564

>From d7f655f5dfc86edcc68bc35916d13ee5fbd6abe8 Mon Sep 17 00:00:00 2001
From: Farzon Lotfi <[email protected]>
Date: Wed, 10 Dec 2025 00:41:04 -0500
Subject: [PATCH 1/2] [HLSL][Matrix] Support row and column indexing modes for
 MatrixSubscriptExpr

fixes #167617

In DXC HLSL supports different indexing modes via codegen for its
equivalent of the MatrixSubscriptExpr when the /Zpr and /Zpc flags are
used see: https://godbolt.org/z/bz5Y5WG36.

This change modifies EmitMatrixSubscriptExpr to consider the
MatrixRowMajor/MatrixColMajor Layout flags before generating an index.

Similarly it introduces `createRowMajorIndex` and
`createColumnMajorIndex` in `MatrixBuilder.h` for use in
`VisitMatrixSubscriptExpr`.
---
 clang/lib/CodeGen/CGExpr.cpp                  | 18 ++++--
 clang/lib/CodeGen/CGExprScalar.cpp            | 13 +++-
 clang/test/CodeGen/matrix-type-indexing.c     | 60 +++++++++++++++++++
 .../test/CodeGenCXX/matrix-type-indexing.cpp  | 36 +++++++++++
 .../BasicFeatures/matrix-type-indexing.hlsl   | 52 ++++++++++++++++
 llvm/include/llvm/IR/MatrixBuilder.h          | 17 +++++-
 6 files changed, 187 insertions(+), 9 deletions(-)
 create mode 100644 clang/test/CodeGen/matrix-type-indexing.c
 create mode 100644 clang/test/CodeGenCXX/matrix-type-indexing.cpp
 create mode 100644 
clang/test/CodeGenHLSL/BasicFeatures/matrix-type-indexing.hlsl

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 27ee96cb6dc82..3cf835c1ba516 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -4977,11 +4977,19 @@ LValue CodeGenFunction::EmitMatrixSubscriptExpr(const 
MatrixSubscriptExpr *E) {
   llvm::Value *RowIdx = EmitMatrixIndexExpr(E->getRowIdx());
   llvm::Value *ColIdx = EmitMatrixIndexExpr(E->getColumnIdx());
 
-  llvm::Value *NumRows = Builder.getIntN(
-      RowIdx->getType()->getScalarSizeInBits(),
-      E->getBase()->getType()->castAs<ConstantMatrixType>()->getNumRows());
-  llvm::Value *FinalIdx =
-      Builder.CreateAdd(Builder.CreateMul(ColIdx, NumRows), RowIdx);
+  llvm::Value *FinalIdx;
+  if (getLangOpts().getDefaultMatrixMemoryLayout() ==
+      LangOptions::MatrixMemoryLayout::MatrixRowMajor) {
+    llvm::Value *NumCols = Builder.getIntN(
+        RowIdx->getType()->getScalarSizeInBits(),
+        
E->getBase()->getType()->castAs<ConstantMatrixType>()->getNumColumns());
+    FinalIdx = Builder.CreateAdd(Builder.CreateMul(RowIdx, NumCols), ColIdx);
+  } else {
+    llvm::Value *NumRows = Builder.getIntN(
+        RowIdx->getType()->getScalarSizeInBits(),
+        E->getBase()->getType()->castAs<ConstantMatrixType>()->getNumRows());
+    FinalIdx = Builder.CreateAdd(Builder.CreateMul(ColIdx, NumRows), RowIdx);
+  }
   return LValue::MakeMatrixElt(
       MaybeConvertMatrixAddress(Base.getAddress(), *this), FinalIdx,
       E->getBase()->getType(), Base.getBaseInfo(), TBAAAccessInfo());
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp 
b/clang/lib/CodeGen/CGExprScalar.cpp
index 1de1378d25249..72aad9707a67e 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2155,9 +2155,18 @@ Value 
*ScalarExprEmitter::VisitMatrixSubscriptExpr(MatrixSubscriptExpr *E) {
   Value *ColumnIdx = CGF.EmitMatrixIndexExpr(E->getColumnIdx());
 
   const auto *MatrixTy = E->getBase()->getType()->castAs<ConstantMatrixType>();
-  unsigned NumRows = MatrixTy->getNumRows();
   llvm::MatrixBuilder MB(Builder);
-  Value *Idx = MB.CreateIndex(RowIdx, ColumnIdx, NumRows);
+
+  Value *Idx;
+  if (CGF.getLangOpts().getDefaultMatrixMemoryLayout() ==
+      LangOptions::MatrixMemoryLayout::MatrixRowMajor) {
+    unsigned NumCols = MatrixTy->getNumColumns();
+    Idx = MB.createRowMajorIndex(RowIdx, ColumnIdx, NumCols);
+  } else {
+    unsigned NumRows = MatrixTy->getNumRows();
+    Idx = MB.createColumnMajorIndex(RowIdx, ColumnIdx, NumRows);
+  }
+
   if (CGF.CGM.getCodeGenOpts().OptimizationLevel > 0)
     MB.CreateIndexAssumption(Idx, MatrixTy->getNumElementsFlattened());
 
diff --git a/clang/test/CodeGen/matrix-type-indexing.c 
b/clang/test/CodeGen/matrix-type-indexing.c
new file mode 100644
index 0000000000000..d76d14c3f67ef
--- /dev/null
+++ b/clang/test/CodeGen/matrix-type-indexing.c
@@ -0,0 +1,60 @@
+// RUN: %clang_cc1 -fenable-matrix -fmatrix-memory-layout=row-major -triple 
x86_64-apple-darwin %s -emit-llvm -disable-llvm-passes -o - | FileCheck %s 
--check-prefixes=CHECK,ROW-CHECK
+// RUN: %clang_cc1 -fenable-matrix -fmatrix-memory-layout=column-major -triple 
x86_64-apple-darwin %s -emit-llvm -disable-llvm-passes -o - | FileCheck %s 
--check-prefixes=CHECK,COL-CHECK
+// RUN: %clang_cc1 -fenable-matrix -triple x86_64-apple-darwin %s -emit-llvm 
-disable-llvm-passes -o - | FileCheck %s --check-prefixes=CHECK,COL-CHECK
+
+typedef float fx2x3_t __attribute__((matrix_type(2, 3)));
+ float Out[6];
+
+ fx2x3_t gM;
+
+void binaryOpMatrixSubscriptExpr(int index, fx2x3_t M) {
+    // CHECK-LABEL: binaryOpMatrixSubscriptExpr
+    // CHECK: %row = alloca i32, align 4
+    // CHECK: %col = alloca i32, align 4
+    // CHECK: [[row_load:%.*]] = load i32, ptr %row, align 4
+    // CHECK-NEXT: [[row_load_zext:%.*]] = zext i32 [[row_load]] to i64
+    // CHECK-NEXT: [[col_load:%.*]] = load i32, ptr %col, align 4
+    // CHECK-NEXT: [[col_load_zext:%.*]] = zext i32 [[col_load]] to i64
+    // COL-CHECK-NEXT: [[col_offset:%.*]] = mul i64 [[col_load_zext]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i64 [[col_offset]], 
[[row_load_zext]]
+    // ROW-CHECK-NEXT: [[row_offset:%.*]] = mul i64 [[row_load_zext]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i64 [[row_offset]], 
[[col_load_zext]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x float>, ptr %M.addr, 
align 4
+    // COL-CHECK-NEXT: %matrixext = extractelement <6 x float> 
[[matrix_as_vec]], i64 [[col_major_index]]
+    // ROW-CHECK-NEXT: %matrixext = extractelement <6 x float> 
[[matrix_as_vec]], i64 [[row_major_index]]
+    const unsigned int COLS = 3;
+    unsigned int row = index / COLS;
+    unsigned int col = index % COLS;
+    Out[index] = M[row][col];
+}
+
+float returnMatrixSubscriptExpr(int row, int col, fx2x3_t M) {
+    // CHECK-LABEL: returnMatrixSubscriptExpr
+    // CHECK: [[row_load:%.*]] = load i32, ptr [[row_ptr:%.*]], align 4
+    // CHECK-NEXT: [[row_load_sext:%.*]] = sext i32 [[row_load]] to i64
+    // CHECK-NEXT: [[col_load:%.*]] = load i32, ptr [[col_ptr:%.*]], align 4
+    // CHECK-NEXT: [[col_load_sext:%.*]] = sext i32 [[col_load]] to i64
+    // COL-CHECK-NEXT: [[col_offset:%.*]] = mul i64 [[col_load_sext]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i64 [[col_offset]], 
[[row_load_sext]]
+    // ROW-CHECK-NEXT: [[row_offset:%.*]] = mul i64 [[row_load_sext]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i64 [[row_offset]], 
[[col_load_sext]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x float>, ptr %M.addr, 
align 4
+    // COL-CHECK-NEXT: [[matrix_after_extract:%.*]] = extractelement <6 x 
float> [[matrix_as_vec]], i64 [[col_major_index]]
+    // ROW-CHECK-NEXT: [[matrix_after_extract:%.*]] = extractelement <6 x 
float> [[matrix_as_vec]], i64 [[row_major_index]]
+    // CHECK-NEXT: ret float [[matrix_after_extract]]
+    return M[row][col];
+}
+
+void storeAtMatrixSubscriptExpr(int row, int col, float value) {
+    // CHECK-LABEL: storeAtMatrixSubscriptExpr
+    // CHECK: [[value_load:%.*]] = load float, ptr [[value_ptr:%.*]], align 4
+    // ROW-CHECK: [[row_offset:%.*]] = mul i64 [[row_load:%.*]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i64 [[row_offset]], 
[[col_load:%.*]]
+    // COL-CHECK: [[col_offset:%.*]] = mul i64 [[col_load:%.*]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i64 [[col_offset]], 
[[row_load:%.*]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x float>, ptr @gM, align 4
+    // ROW-CHECK-NEXT: [[matrix_after_insert:%.*]] = insertelement <6 x float> 
[[matrix_as_vec]], float [[value_load]], i64 [[row_major_index]]
+    // COL-CHECK-NEXT: [[matrix_after_insert:%.*]] = insertelement <6 x float> 
[[matrix_as_vec]], float [[value_load]], i64 [[col_major_index]]
+    // CHECK-NEXT: store <6 x float> [[matrix_after_insert]], ptr @gM, align 4
+    gM[row][col] = value;
+}
diff --git a/clang/test/CodeGenCXX/matrix-type-indexing.cpp 
b/clang/test/CodeGenCXX/matrix-type-indexing.cpp
new file mode 100644
index 0000000000000..a390bcaf89119
--- /dev/null
+++ b/clang/test/CodeGenCXX/matrix-type-indexing.cpp
@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -fenable-matrix  -fmatrix-memory-layout=column-major 
-triple x86_64-apple-darwin %s -emit-llvm -disable-llvm-passes -o - -std=c++11 
| FileCheck %s
+// RUN: %clang_cc1 -fenable-matrix -triple x86_64-apple-darwin %s -emit-llvm 
-disable-llvm-passes -o - -std=c++11 | FileCheck %s
+
+ typedef float fx2x3_t __attribute__((matrix_type(2, 3)));
+ float Out[6];
+
+void binaryOpMatrixSubscriptExpr(int index, fx2x3_t M) {
+    // CHECK-LABEL: binaryOpMatrixSubscriptExpr
+    // CHECK: %row = alloca i32, align 4
+    // CHECK: %col = alloca i32, align 4
+    // CHECK: [[row_load:%.*]] = load i32, ptr %row, align 4
+    // CHECK-NEXT: [[row_load_zext:%.*]] = zext i32 [[row_load]] to i64
+    // CHECK-NEXT: [[col_load:%.*]] = load i32, ptr %col, align 4
+    // CHECK-NEXT: [[col_load_zext:%.*]] = zext i32 [[col_load]] to i64
+    // CHECK-NEXT: [[col_offset:%.*]] = mul i64 [[col_load_zext]], 2
+    // CHECK-NEXT: [[col_major_index:%.*]] = add i64 [[col_offset]], 
[[row_load_zext]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x float>, ptr %M.addr, 
align 4
+    // CHECK-NEXT: %matrixext = extractelement <6 x float> [[matrix_as_vec]], 
i64 [[col_major_index]]
+    const unsigned int COLS = 3;
+    unsigned int row = index / COLS;
+    unsigned int col = index % COLS;
+    Out[index] = M[row][col];
+}
+
+float returnMatrixSubscriptExpr(int row, int col, fx2x3_t M) {
+    // CHECK-LABEL: returnMatrixSubscriptExpr
+    // CHECK: [[row_load:%.*]] = load i32, ptr %row.addr, align 4
+    // CHECK-NEXT: [[row_load_sext:%.*]] = sext i32 [[row_load]] to i64
+    // CHECK-NEXT: [[col_load:%.*]] = load i32, ptr %col.addr, align 4
+    // CHECK-NEXT: [[col_load_sext:%.*]] = sext i32 [[col_load]] to i64
+    // CHECK-NEXT: [[col_offset:%.*]] = mul i64 [[col_load_sext]], 2
+    // CHECK-NEXT: [[col_major_index:%.*]] = add i64 [[col_offset]], 
[[row_load_sext]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x float>, ptr %M.addr, 
align 4
+    // CHECK-NEXT: %matrixext = extractelement <6 x float> [[matrix_as_vec]], 
i64 [[col_major_index]]
+    return M[row][col];
+}
diff --git a/clang/test/CodeGenHLSL/BasicFeatures/matrix-type-indexing.hlsl 
b/clang/test/CodeGenHLSL/BasicFeatures/matrix-type-indexing.hlsl
new file mode 100644
index 0000000000000..7a63bbb45ecf7
--- /dev/null
+++ b/clang/test/CodeGenHLSL/BasicFeatures/matrix-type-indexing.hlsl
@@ -0,0 +1,52 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple 
dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm 
-disable-llvm-passes -fmatrix-memory-layout=row-major -o - | FileCheck %s 
--check-prefixes=CHECK,ROW-CHECK
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple 
dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm 
-disable-llvm-passes -fmatrix-memory-layout=column-major -o - | FileCheck %s 
--check-prefixes=CHECK,COL-CHECK
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple 
dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm 
-disable-llvm-passes -o - | FileCheck %s --check-prefixes=CHECK,COL-CHECK
+
+RWBuffer<int> Out : register(u1);
+half2x3 gM;
+
+
+void binaryOpMatrixSubscriptExpr(int index, half2x3 M) {
+    // CHECK-LABEL: binaryOpMatrixSubscriptExpr
+    // CHECK: %row = alloca i32, align 4
+    // CHECK: %col = alloca i32, align 4
+    // CHECK: [[row_load:%.*]] = load i32, ptr %row, align 4
+    // CHECK-NEXT: [[col_load:%.*]] = load i32, ptr %col, align 4
+    // ROW-CHECK-NEXT: [[row_offset:%.*]] = mul i32 [[row_load]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i32 [[row_offset]], 
[[col_load]]
+    // COL-CHECK-NEXT: [[col_offset:%.*]] = mul i32 [[col_load]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i32 [[col_offset]], 
[[row_load]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x half>, ptr %M.addr, align 
2
+    // ROW-CHECK-NEXT: %matrixext = extractelement <6 x half> 
[[matrix_as_vec]], i32 [[row_major_index]]
+    // COL-CHECK-NEXT: %matrixext = extractelement <6 x half> 
[[matrix_as_vec]], i32 [[col_major_index]]
+    const uint COLS = 3;
+    uint row = index / COLS;
+    uint col = index % COLS;
+    Out[index] = M[row][col];
+}
+
+half returnMatrixSubscriptExpr(int row, int col, half2x3 M) {
+    // CHECK-LABEL: returnMatrixSubscriptExpr
+    // ROW-CHECK: [[row_offset:%.*]] = mul i32 [[row_load:%.*]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i32 [[row_offset]], 
[[col_load:%.*]]
+    // COL-CHECK: [[col_offset:%.*]] = mul i32 [[col_load:%.*]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i32 [[col_offset]], 
[[row_load:%.*]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x half>, ptr %M.addr, align 
2
+    // ROW-CHECK-NEXT: %matrixext = extractelement <6 x half> 
[[matrix_as_vec]], i32 [[row_major_index]]
+    // COL-CHECK-NEXT: %matrixext = extractelement <6 x half> 
[[matrix_as_vec]], i32 [[col_major_index]]
+    return M[row][col];
+}
+
+void storeAtMatrixSubscriptExpr(int row, int col, half value) {
+    // CHECK-LABEL: storeAtMatrixSubscriptExpr
+    // CHECK: [[value_load:%.*]] = load half, ptr [[value_ptr:%.*]], align 2
+    // ROW-CHECK: [[row_offset:%.*]] = mul i32 [[row_load:%.*]], 3
+    // ROW-CHECK-NEXT: [[row_major_index:%.*]] = add i32 [[row_offset]], 
[[col_load:%.*]]
+    // COL-CHECK: [[col_offset:%.*]] = mul i32 [[col_load:%.*]], 2
+    // COL-CHECK-NEXT: [[col_major_index:%.*]] = add i32 [[col_offset]], 
[[row_load:%.*]]
+    // CHECK-NEXT: [[matrix_as_vec:%.*]] = load <6 x half>, ptr addrspace(2) 
@gM, align 2
+    // ROW-CHECK-NEXT: [[matrix_after_insert:%.*]] = insertelement <6 x half> 
[[matrix_as_vec]], half [[value_load]], i32 [[row_major_index]]
+    // COL-CHECK-NEXT: [[matrix_after_insert:%.*]] = insertelement <6 x half> 
[[matrix_as_vec]], half [[value_load]], i32 [[col_major_index]]
+    // CHECK-NEXT: store <6 x half> [[matrix_after_insert]], ptr addrspace(2) 
@gM, align 2
+    gM[row][col] = value;
+}
diff --git a/llvm/include/llvm/IR/MatrixBuilder.h 
b/llvm/include/llvm/IR/MatrixBuilder.h
index 3a04ca87f2b55..0cea0f0ddafa3 100644
--- a/llvm/include/llvm/IR/MatrixBuilder.h
+++ b/llvm/include/llvm/IR/MatrixBuilder.h
@@ -241,8 +241,8 @@ class MatrixBuilder {
 
   /// Compute the index to access the element at (\p RowIdx, \p ColumnIdx) from
   /// a matrix with \p NumRows embedded in a vector.
-  Value *CreateIndex(Value *RowIdx, Value *ColumnIdx, unsigned NumRows,
-                     Twine const &Name = "") {
+  Value *createColumnMajorIndex(Value *RowIdx, Value *ColumnIdx,
+                                unsigned NumRows, Twine const &Name = "") {
     unsigned MaxWidth = std::max(RowIdx->getType()->getScalarSizeInBits(),
                                  ColumnIdx->getType()->getScalarSizeInBits());
     Type *IntTy = IntegerType::get(RowIdx->getType()->getContext(), MaxWidth);
@@ -251,6 +251,19 @@ class MatrixBuilder {
     Value *NumRowsV = B.getIntN(MaxWidth, NumRows);
     return B.CreateAdd(B.CreateMul(ColumnIdx, NumRowsV), RowIdx);
   }
+
+  /// Compute the index to access the element at (\p RowIdx, \p ColumnIdx) from
+  /// a matrix with \p NumCols embedded in a vector.
+  Value *createRowMajorIndex(Value *RowIdx, Value *ColumnIdx, unsigned NumCols,
+                             Twine const &Name = "") {
+    unsigned MaxWidth = std::max(RowIdx->getType()->getScalarSizeInBits(),
+                                 ColumnIdx->getType()->getScalarSizeInBits());
+    Type *IntTy = IntegerType::get(RowIdx->getType()->getContext(), MaxWidth);
+    RowIdx = B.CreateZExt(RowIdx, IntTy);
+    ColumnIdx = B.CreateZExt(ColumnIdx, IntTy);
+    Value *NumColsV = B.getIntN(MaxWidth, NumCols);
+    return B.CreateAdd(B.CreateMul(RowIdx, NumColsV), ColumnIdx);
+  }
 };
 
 } // end namespace llvm

>From 66d1eb9e69b03bcfa108c8c7187a2df9bd36f7eb Mon Sep 17 00:00:00 2001
From: Farzon Lotfi <[email protected]>
Date: Fri, 19 Dec 2025 13:58:31 -0500
Subject: [PATCH 2/2] address the new CreateIndex cases

---
 clang/lib/CodeGen/CGExpr.cpp         | 31 ++++++++++++++--------------
 clang/lib/CodeGen/CGExprScalar.cpp   | 18 ++++++++--------
 llvm/include/llvm/IR/MatrixBuilder.h | 30 +++++++++++++++------------
 3 files changed, 42 insertions(+), 37 deletions(-)

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 3cf835c1ba516..518cb50bb7722 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2482,7 +2482,10 @@ RValue CodeGenFunction::EmitLoadOfLValue(LValue LV, 
SourceLocation Loc) {
 
     for (unsigned Col = 0; Col < NumCols; ++Col) {
       llvm::Value *ColIdx = llvm::ConstantInt::get(Row->getType(), Col);
-      llvm::Value *EltIndex = MB.CreateIndex(Row, ColIdx, NumRows);
+      bool IsMatrixRowMajor = getLangOpts().getDefaultMatrixMemoryLayout() ==
+                              LangOptions::MatrixMemoryLayout::MatrixRowMajor;
+      llvm::Value *EltIndex =
+          MB.createIndex(Row, ColIdx, NumRows, NumCols, IsMatrixRowMajor);
       llvm::Value *Elt = Builder.CreateExtractElement(MatrixVec, EltIndex);
       llvm::Value *Lane = llvm::ConstantInt::get(Builder.getInt32Ty(), Col);
       Result = Builder.CreateInsertElement(Result, Elt, Lane);
@@ -2733,7 +2736,10 @@ void CodeGenFunction::EmitStoreThroughLValue(RValue Src, 
LValue Dst,
 
       for (unsigned Col = 0; Col < NumCols; ++Col) {
         llvm::Value *ColIdx = llvm::ConstantInt::get(Row->getType(), Col);
-        llvm::Value *EltIndex = MB.CreateIndex(Row, ColIdx, NumRows);
+        bool IsMatrixRowMajor = getLangOpts().getDefaultMatrixMemoryLayout() ==
+                                
LangOptions::MatrixMemoryLayout::MatrixRowMajor;
+        llvm::Value *EltIndex =
+            MB.createIndex(Row, ColIdx, NumRows, NumCols, IsMatrixRowMajor);
         llvm::Value *Lane = llvm::ConstantInt::get(Builder.getInt32Ty(), Col);
         llvm::Value *NewElt = Builder.CreateExtractElement(RowVal, Lane);
         MatrixVec = Builder.CreateInsertElement(MatrixVec, NewElt, EltIndex);
@@ -4976,20 +4982,15 @@ LValue CodeGenFunction::EmitMatrixSubscriptExpr(const 
MatrixSubscriptExpr *E) {
   // Extend or truncate the index type to 32 or 64-bits if needed.
   llvm::Value *RowIdx = EmitMatrixIndexExpr(E->getRowIdx());
   llvm::Value *ColIdx = EmitMatrixIndexExpr(E->getColumnIdx());
+  llvm::MatrixBuilder MB(Builder);
+  const auto *MatrixTy = E->getBase()->getType()->castAs<ConstantMatrixType>();
+  unsigned NumCols = MatrixTy->getNumColumns();
+  unsigned NumRows = MatrixTy->getNumRows();
+  bool IsMatrixRowMajor = getLangOpts().getDefaultMatrixMemoryLayout() ==
+                          LangOptions::MatrixMemoryLayout::MatrixRowMajor;
+  llvm::Value *FinalIdx =
+      MB.createIndex(RowIdx, ColIdx, NumRows, NumCols, IsMatrixRowMajor);
 
-  llvm::Value *FinalIdx;
-  if (getLangOpts().getDefaultMatrixMemoryLayout() ==
-      LangOptions::MatrixMemoryLayout::MatrixRowMajor) {
-    llvm::Value *NumCols = Builder.getIntN(
-        RowIdx->getType()->getScalarSizeInBits(),
-        
E->getBase()->getType()->castAs<ConstantMatrixType>()->getNumColumns());
-    FinalIdx = Builder.CreateAdd(Builder.CreateMul(RowIdx, NumCols), ColIdx);
-  } else {
-    llvm::Value *NumRows = Builder.getIntN(
-        RowIdx->getType()->getScalarSizeInBits(),
-        E->getBase()->getType()->castAs<ConstantMatrixType>()->getNumRows());
-    FinalIdx = Builder.CreateAdd(Builder.CreateMul(ColIdx, NumRows), RowIdx);
-  }
   return LValue::MakeMatrixElt(
       MaybeConvertMatrixAddress(Base.getAddress(), *this), FinalIdx,
       E->getBase()->getType(), Base.getBaseInfo(), TBAAAccessInfo());
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp 
b/clang/lib/CodeGen/CGExprScalar.cpp
index 72aad9707a67e..c4c97dc3773ae 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2136,7 +2136,10 @@ Value *ScalarExprEmitter::VisitMatrixSingleSubscriptExpr(
 
   for (unsigned Col = 0; Col != NumColumns; ++Col) {
     Value *ColVal = llvm::ConstantInt::get(RowIdx->getType(), Col);
-    Value *EltIdx = MB.CreateIndex(RowIdx, ColVal, NumRows, "matrix_row_idx");
+    bool IsMatrixRowMajor = CGF.getLangOpts().getDefaultMatrixMemoryLayout() ==
+                            LangOptions::MatrixMemoryLayout::MatrixRowMajor;
+    Value *EltIdx = MB.createIndex(RowIdx, ColVal, NumRows, NumColumns,
+                                   IsMatrixRowMajor, "matrix_row_idx");
     Value *Elt =
         Builder.CreateExtractElement(FlatMatrix, EltIdx, "matrix_elem");
     Value *Lane = llvm::ConstantInt::get(Builder.getInt32Ty(), Col);
@@ -2158,14 +2161,11 @@ Value 
*ScalarExprEmitter::VisitMatrixSubscriptExpr(MatrixSubscriptExpr *E) {
   llvm::MatrixBuilder MB(Builder);
 
   Value *Idx;
-  if (CGF.getLangOpts().getDefaultMatrixMemoryLayout() ==
-      LangOptions::MatrixMemoryLayout::MatrixRowMajor) {
-    unsigned NumCols = MatrixTy->getNumColumns();
-    Idx = MB.createRowMajorIndex(RowIdx, ColumnIdx, NumCols);
-  } else {
-    unsigned NumRows = MatrixTy->getNumRows();
-    Idx = MB.createColumnMajorIndex(RowIdx, ColumnIdx, NumRows);
-  }
+  unsigned NumCols = MatrixTy->getNumColumns();
+  unsigned NumRows = MatrixTy->getNumRows();
+  bool IsMatrixRowMajor = CGF.getLangOpts().getDefaultMatrixMemoryLayout() ==
+                          LangOptions::MatrixMemoryLayout::MatrixRowMajor;
+  Idx = MB.createIndex(RowIdx, ColumnIdx, NumRows, NumCols, IsMatrixRowMajor);
 
   if (CGF.CGM.getCodeGenOpts().OptimizationLevel > 0)
     MB.CreateIndexAssumption(Idx, MatrixTy->getNumElementsFlattened());
diff --git a/llvm/include/llvm/IR/MatrixBuilder.h 
b/llvm/include/llvm/IR/MatrixBuilder.h
index 0cea0f0ddafa3..6b6926c2d00a7 100644
--- a/llvm/include/llvm/IR/MatrixBuilder.h
+++ b/llvm/include/llvm/IR/MatrixBuilder.h
@@ -238,30 +238,34 @@ class MatrixBuilder {
     else
       B.CreateAssumption(Cmp);
   }
-
-  /// Compute the index to access the element at (\p RowIdx, \p ColumnIdx) from
-  /// a matrix with \p NumRows embedded in a vector.
-  Value *createColumnMajorIndex(Value *RowIdx, Value *ColumnIdx,
-                                unsigned NumRows, Twine const &Name = "") {
+  Value *createIndex(Value *RowIdx, Value *ColumnIdx, unsigned NumRows,
+                     unsigned NumCols, bool IsMatrixRowMajor = false,
+                     Twine const &Name = "") {
     unsigned MaxWidth = std::max(RowIdx->getType()->getScalarSizeInBits(),
                                  ColumnIdx->getType()->getScalarSizeInBits());
     Type *IntTy = IntegerType::get(RowIdx->getType()->getContext(), MaxWidth);
     RowIdx = B.CreateZExt(RowIdx, IntTy);
     ColumnIdx = B.CreateZExt(ColumnIdx, IntTy);
+    if (IsMatrixRowMajor) {
+      Value *NumColsV = B.getIntN(MaxWidth, NumCols);
+      return createRowMajorIndex(RowIdx, ColumnIdx, NumColsV, Name);
+    }
     Value *NumRowsV = B.getIntN(MaxWidth, NumRows);
+    return createColumnMajorIndex(RowIdx, ColumnIdx, NumRowsV, Name);
+  }
+
+private:
+  /// Compute the index to access the element at (\p RowIdx, \p ColumnIdx) from
+  /// a matrix with \p NumRows embedded in a vector.
+  Value *createColumnMajorIndex(Value *RowIdx, Value *ColumnIdx,
+                                Value *NumRowsV, Twine const &Name) {
     return B.CreateAdd(B.CreateMul(ColumnIdx, NumRowsV), RowIdx);
   }
 
   /// Compute the index to access the element at (\p RowIdx, \p ColumnIdx) from
   /// a matrix with \p NumCols embedded in a vector.
-  Value *createRowMajorIndex(Value *RowIdx, Value *ColumnIdx, unsigned NumCols,
-                             Twine const &Name = "") {
-    unsigned MaxWidth = std::max(RowIdx->getType()->getScalarSizeInBits(),
-                                 ColumnIdx->getType()->getScalarSizeInBits());
-    Type *IntTy = IntegerType::get(RowIdx->getType()->getContext(), MaxWidth);
-    RowIdx = B.CreateZExt(RowIdx, IntTy);
-    ColumnIdx = B.CreateZExt(ColumnIdx, IntTy);
-    Value *NumColsV = B.getIntN(MaxWidth, NumCols);
+  Value *createRowMajorIndex(Value *RowIdx, Value *ColumnIdx, Value *NumColsV,
+                             Twine const &Name) {
     return B.CreateAdd(B.CreateMul(RowIdx, NumColsV), ColumnIdx);
   }
 };

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