Stress test for nested module hierarchies

I'm optimizing a case that is well approximated by
multiple layers of modules where every module in a layer
imports all the modules in the layer below.

It turns out I regressed performance on such cases in 7fea7121.
I'm adding a test case to track improvements and prevent
future regressions.

Test Plan: ./validate

Reviewers: simonmar, austin, bgamari

Reviewed By: simonmar

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3575

2 files changed, 33 insertions, 0 deletions

diff --git a/testsuite/tests/perf/compiler/all.T b/testsuite/tests/perf/compiler/all.T
index 360bef4702..c90378bbb3 100644
--- a/testsuite/tests/perf/compiler/all.T
+++ b/testsuite/tests/perf/compiler/all.T
@@ -1096,3 +1096,15 @@ test('T13379',
      ],
      compile,
      [''])
+
+test('MultiLayerModules',
+     [ compiler_stats_num_field('bytes allocated',
+          [(wordsize(64), 6956533312, 10),
+          # initial:    12139116496
+          # 2017-05-12: 6956533312   Revert "Use a deterministic map for imp_dep_mods"
+          ]),
+       pre_cmd('./genMultiLayerModules'),
+       extra_files(['genMultiLayerModules']),
+     ],
+     multimod_compile,
+     ['MultiLayerModules', '-v0'])
diff --git a/testsuite/tests/perf/compiler/genMultiLayerModules b/testsuite/tests/perf/compiler/genMultiLayerModules
new file mode 100755
index 0000000000..b98c481166
--- /dev/null
+++ b/testsuite/tests/perf/compiler/genMultiLayerModules
@@ -0,0 +1,21 @@
+#!/bin/bash
+# Generate $DEPTH layers of modules with $WIDTH modules on each layer
+# Every module on layer N imports all the modules on layer N-1
+# MultiLayerModules.hs imports all the modules from the last layer
+DEPTH=15
+WIDTH=40
+for i in $(seq -w 1 $WIDTH); do
+  echo "module DummyLevel0M$i where" > DummyLevel0M$i.hs;
+done
+for l in $(seq 1 $DEPTH); do
+  for i in $(seq -w 1 $WIDTH); do
+    echo "module DummyLevel${l}M$i where" > DummyLevel${l}M$i.hs;
+    for j in $(seq -w 1 $WIDTH); do
+      echo "import DummyLevel$((l-1))M$j" >> DummyLevel${l}M$i.hs;
+    done
+  done
+done
+echo "module MultiLayerModules where" > MultiLayerModules.hs
+for j in $(seq -w 1 $WIDTH); do
+  echo "import DummyLevel${DEPTH}M$j" >> MultiLayerModules.hs;
+done