From 8647b966ab6f1a1421ad192ee3777a4952b315e1 Mon Sep 17 00:00:00 2001
From: Kristoffer Carlsson <kristoffer.carlsson@chalmers.se>
Date: Fri, 19 Oct 2018 16:47:53 -0400
Subject: [PATCH] improve performance for sorting columns in sparse matrix
 (#29682)

(cherry picked from commit 2885b62bd3b3c99640f63017a96a584c6f10c10a)
---
 stdlib/SparseArrays/src/sparsematrix.jl | 40 +++++++++++++++----------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/stdlib/SparseArrays/src/sparsematrix.jl b/stdlib/SparseArrays/src/sparsematrix.jl
index 5b107ff86d258..bbc5135229beb 100644
--- a/stdlib/SparseArrays/src/sparsematrix.jl
+++ b/stdlib/SparseArrays/src/sparsematrix.jl
@@ -3401,37 +3401,47 @@ function sortSparseMatrixCSC!(A::SparseMatrixCSC{Tv,Ti}; sortindices::Symbol = :
     row = zeros(Ti, m)
     val = zeros(Tv, m)
 
-    for i = 1:n
-        @inbounds col_start = colptr[i]
-        @inbounds col_end = (colptr[i+1] - 1)
+    perm = Base.Perm(Base.ord(isless, identity, false, Base.Order.Forward), row)
 
-        numrows = col_end - col_start + 1
+    @inbounds for i = 1:n
+        nzr = nzrange(A, i)
+        numrows = length(nzr)
         if numrows <= 1
             continue
         elseif numrows == 2
-            f = col_start
+            f = first(nzr)
             s = f+1
             if rowval[f] > rowval[s]
-                @inbounds rowval[f], rowval[s] = rowval[s], rowval[f]
-                @inbounds nzval[f],  nzval[s]  = nzval[s],  nzval[f]
+                rowval[f], rowval[s] = rowval[s], rowval[f]
+                nzval[f],  nzval[s]  = nzval[s],  nzval[f]
             end
             continue
         end
+        resize!(row, numrows)
+        resize!(index, numrows)
 
         jj = 1
-        @simd for j = col_start:col_end
-            @inbounds row[jj] = rowval[j]
-            @inbounds val[jj] = nzval[j]
+        @simd for j = nzr
+            row[jj] = rowval[j]
+            val[jj] = nzval[j]
             jj += 1
         end
 
-        sortperm!(unsafe_wrap(Vector{Ti}, pointer(index), numrows),
-                  unsafe_wrap(Vector{Ti}, pointer(row), numrows))
+        if numrows <= 16
+            alg = Base.Sort.InsertionSort
+        else
+            alg = Base.Sort.QuickSort
+        end
+
+        # Reset permutation
+        index .= 1:numrows
+
+        sort!(index, alg, perm)
 
         jj = 1
-        @simd for j = col_start:col_end
-            @inbounds rowval[j] = row[index[jj]]
-            @inbounds nzval[j] = val[index[jj]]
+        @simd for j = nzr
+            rowval[j] = row[index[jj]]
+            nzval[j] = val[index[jj]]
             jj += 1
         end
     end