From 8ea8f55205a212b1d3faa9f044de1436b9c9e8b4 Mon Sep 17 00:00:00 2001
From: Jishnu Bhattacharya <jishnub.github@gmail.com>
Date: Mon, 14 Apr 2025 16:55:49 +0530
Subject: [PATCH 1/3] Unaliasing and short-circuiting in `copytrito!`

---
 src/generic.jl  | 14 ++++++++++----
 test/generic.jl |  9 +++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/generic.jl b/src/generic.jl
index de3b195c..44206d6a 100644
--- a/src/generic.jl
+++ b/src/generic.jl
@@ -2088,20 +2088,21 @@ julia> copytrito!(B, A, 'L')
 function copytrito!(B::AbstractMatrix, A::AbstractMatrix, uplo::AbstractChar)
     require_one_based_indexing(A, B)
     BLAS.chkuplo(uplo)
+    B === A && return B
     m,n = size(A)
     A = Base.unalias(B, A)
     if uplo == 'U'
         LAPACK.lacpy_size_check(size(B), (n < m ? n : m, n))
+        # extract the parents for UpperTriangular matrices
+        Bv, Av = uppertridata(B), uppertridata(A)
         for j in axes(A,2), i in axes(A,1)[begin : min(j,end)]
-            # extract the parents for UpperTriangular matrices
-            Bv, Av = uppertridata(B), uppertridata(A)
             @inbounds Bv[i,j] = Av[i,j]
         end
     else # uplo == 'L'
         LAPACK.lacpy_size_check(size(B), (m, m < n ? m : n))
+        # extract the parents for LowerTriangular matrices
+        Bv, Av = lowertridata(B), lowertridata(A)
         for j in axes(A,2), i in axes(A,1)[j:end]
-            # extract the parents for LowerTriangular matrices
-            Bv, Av = lowertridata(B), lowertridata(A)
             @inbounds Bv[i,j] = Av[i,j]
         end
     end
@@ -2109,5 +2110,10 @@ function copytrito!(B::AbstractMatrix, A::AbstractMatrix, uplo::AbstractChar)
 end
 # Forward LAPACK-compatible strided matrices to lacpy
 function copytrito!(B::StridedMatrixStride1{T}, A::StridedMatrixStride1{T}, uplo::AbstractChar) where {T<:BlasFloat}
+    require_one_based_indexing(A, B)
+    BLAS.chkuplo(uplo)
+    B === A && return B
+    A = Base.unalias(B, A)
     LAPACK.lacpy!(B, A, uplo)
+    return B
 end
diff --git a/test/generic.jl b/test/generic.jl
index 11194a60..fdb079ba 100644
--- a/test/generic.jl
+++ b/test/generic.jl
@@ -879,4 +879,13 @@ end
     @test mul!(copy!(similar(v), v), v, 2, 2, 0) == 4v
 end
 
+@testset "aliasing in copytrito! for strided matrices" begin
+    M = rand(4, 1)
+    A = view(M, 1:3, 1:1)
+    A2 = copy(A)
+    B = view(M, 2:4, 1:1)
+    copytrito!(B, A, 'L')
+    @test B == A2
+end
+
 end # module TestGeneric

From 268050a8be1b9d97a822640bc2c99d77f5a0f755 Mon Sep 17 00:00:00 2001
From: Jishnu Bhattacharya <jishnub.github@gmail.com>
Date: Mon, 14 Apr 2025 18:04:42 +0530
Subject: [PATCH 2/3] Move `chkuplo` to `lacpy!`

---
 src/generic.jl | 1 -
 src/lapack.jl  | 1 +
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/generic.jl b/src/generic.jl
index 44206d6a..56a6b10f 100644
--- a/src/generic.jl
+++ b/src/generic.jl
@@ -2111,7 +2111,6 @@ end
 # Forward LAPACK-compatible strided matrices to lacpy
 function copytrito!(B::StridedMatrixStride1{T}, A::StridedMatrixStride1{T}, uplo::AbstractChar) where {T<:BlasFloat}
     require_one_based_indexing(A, B)
-    BLAS.chkuplo(uplo)
     B === A && return B
     A = Base.unalias(B, A)
     LAPACK.lacpy!(B, A, uplo)
diff --git a/src/lapack.jl b/src/lapack.jl
index 001cfc82..fcbc4db5 100644
--- a/src/lapack.jl
+++ b/src/lapack.jl
@@ -7176,6 +7176,7 @@ for (fn, elty) in ((:dlacpy_, :Float64),
         function lacpy!(B::AbstractMatrix{$elty}, A::AbstractMatrix{$elty}, uplo::AbstractChar)
             require_one_based_indexing(A, B)
             chkstride1(A, B)
+            chkuplo(uplo)
             m, n = size(A)
             m1, n1 = size(B)
             if uplo == 'U'

From 6bf623af1d07000bc2199e04ce1b321b34440a8e Mon Sep 17 00:00:00 2001
From: Jishnu Bhattacharya <jishnub.github@gmail.com>
Date: Mon, 14 Apr 2025 21:43:44 +0530
Subject: [PATCH 3/3] Revert "Move `chkuplo` to `lacpy!`"

This reverts commit 4aa966fbd8a13ccf65737be1ea029d209d390c00.
---
 src/generic.jl | 1 +
 src/lapack.jl  | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/generic.jl b/src/generic.jl
index 56a6b10f..44206d6a 100644
--- a/src/generic.jl
+++ b/src/generic.jl
@@ -2111,6 +2111,7 @@ end
 # Forward LAPACK-compatible strided matrices to lacpy
 function copytrito!(B::StridedMatrixStride1{T}, A::StridedMatrixStride1{T}, uplo::AbstractChar) where {T<:BlasFloat}
     require_one_based_indexing(A, B)
+    BLAS.chkuplo(uplo)
     B === A && return B
     A = Base.unalias(B, A)
     LAPACK.lacpy!(B, A, uplo)
diff --git a/src/lapack.jl b/src/lapack.jl
index fcbc4db5..001cfc82 100644
--- a/src/lapack.jl
+++ b/src/lapack.jl
@@ -7176,7 +7176,6 @@ for (fn, elty) in ((:dlacpy_, :Float64),
         function lacpy!(B::AbstractMatrix{$elty}, A::AbstractMatrix{$elty}, uplo::AbstractChar)
             require_one_based_indexing(A, B)
             chkstride1(A, B)
-            chkuplo(uplo)
             m, n = size(A)
             m1, n1 = size(B)
             if uplo == 'U'