Check if a buffer for the decompression of acyclic coloring is needed

Author: amontoison

src/decompression.jl

@@ -575,7 +575,7 @@ function decompress!(
     nzA = nonzeros(A)
     uplo == :F && check_same_pattern(A, S)
 
-    if eltype(buffer) == R
+    if eltype(buffer) == R || isempty(buffer)
         buffer_right_type = buffer
     else
         buffer_right_type = similar(buffer, R)

src/result.jl

@@ -361,7 +361,8 @@ function TreeSetColoringResult(
 
     # buffer holds the sum of edge values for subtrees in a tree.
     # For each vertex i, buffer[i] is the sum of edge values in the subtree rooted at i.
-    buffer = Vector{R}(undef, nvertices)
+    # Note that we don't need a buffer is all trees are stars
+    buffer = all(is_star) ? R[] : Vector{R}(undef, nvertices)
 
     return TreeSetColoringResult(
         A,

test/allocations.jl

@@ -132,3 +132,16 @@ end;
         test_noallocs_structured_decompression(1000; structure, partition, decompression)
     end
 end;
+
+@testset "Multi-precision acyclic decompression" begin
+    A = sparse([0 0 1; 0 1 0; 1 0 0])
+    problem = ColoringProblem(; structure=:symmetric, partition=:column)
+    result = coloring(A, problem, GreedyColoringAlgorithm{:substitution}())
+    @test isempty(result.buffer)
+    for T in (Float32, Float64)
+        C = rand(T) * T.(A)
+        B = compress(C, result)
+        bench_multiprecision = @be decompress!(C, B, result)
+        @test minimum(bench_multiprecision).allocs == 0
+    end
+end