4 files changed, 88 insertions, 1 deletions
diff --git a/testsuite/tests/perf/compiler/InstanceMatching.stderr b/testsuite/tests/perf/compiler/InstanceMatching.stderr
new file mode 100644
index 0000000000..f4e978cf2e
--- /dev/null
+++ b/testsuite/tests/perf/compiler/InstanceMatching.stderr
@@ -0,0 +1,5 @@
+
+Match.hs:1006:1: error:
+    • No instance for (Show (F001 a)) arising from a use of ‘showsPrec’
+    • In the first argument of ‘(.)’, namely ‘(showsPrec 11 b1)’
+      In the second argument of ‘(.)’, namely
diff --git a/testsuite/tests/perf/compiler/Makefile b/testsuite/tests/perf/compiler/Makefile
index 0011c70710..33d2878db7 100644
--- a/testsuite/tests/perf/compiler/Makefile
+++ b/testsuite/tests/perf/compiler/Makefile
@@ -28,3 +28,8 @@ MultiLayerModulesTH_Make_Prep:
 MultiLayerModulesTH_OneShot_Prep: MultiLayerModulesTH_Make_Prep
 	$(CP) MultiLayerModules.hs MultiLayerModulesTH_OneShot.hs
 
+# Type family skolems
+InstanceMatching:
+	./genMatchingTest 0
+	'$(TEST_HC)' $(TEST_HC_OPTS) -fno-code -fwrite-interface Defs.hs
+
diff --git a/testsuite/tests/perf/compiler/all.T b/testsuite/tests/perf/compiler/all.T
index 4136572419..532db501e6 100644
--- a/testsuite/tests/perf/compiler/all.T
+++ b/testsuite/tests/perf/compiler/all.T
@@ -282,6 +282,7 @@ test('MultiLayerModules',
      multimod_compile,
      ['MultiLayerModules', '-v0'])
 
+
 # MultiLayerModules flip flops by 2.5%, depending on the
 # number of modules within GHC (#19293). Just widen the
 # acceptance window until we figured out how to fix it.
@@ -334,6 +335,30 @@ test('MultiLayerModulesDefsGhci',
      ghci_script,
      ['MultiLayerModulesDefsGhci.script'])
 
+test('InstanceMatching',
+     [ collect_compiler_stats('bytes allocated',3),
+       pre_cmd('$MAKE -s --no-print-directory InstanceMatching'),
+       extra_files(['genMatchingTest']),
+       compile_timeout_multiplier(5),
+       grep_errmsg('F001')],
+     multimod_compile_fail,
+     ['Match', '-fno-code -fwrite-interface -v0'])
+
+# This module stresses the KnownTC and NoKnownTC (skolem variable) cases
+test('InstanceMatching1',
+     [ collect_compiler_stats('bytes allocated',3),
+       pre_cmd('./genMatchingTest 1'),
+       extra_files(['genMatchingTest']),
+       compile_timeout_multiplier(5)
+       # this is _a lot_
+       # but this test has been failing every now and then,
+       # especially on i386. Let's just give it some room
+       # to complete successfully reliably everywhere.
+     ],
+     multimod_compile,
+     ['Defs', '-fno-code -fwrite-interface -v0'])
+
+
 test('MultiLayerModulesNoCode',
      [ collect_compiler_residency(15),
        pre_cmd('./genMultiLayerModulesNoCode'),
@@ -558,7 +583,7 @@ test('hard_hole_fits', # Testing multiple hole-fits with lots in scope for #1687
 test('T16875',  # Testing one hole-fit with a lot in scope for #16875
      collect_compiler_stats('bytes allocated', 2),
      compile, ['-fdefer-type-errors -fno-max-valid-hole-fits -package ghc'])
-test ('T20261', 
+test ('T20261',
       [collect_compiler_stats('all')],
       compile,
       [''])
diff --git a/testsuite/tests/perf/compiler/genMatchingTest b/testsuite/tests/perf/compiler/genMatchingTest
new file mode 100755
index 0000000000..9356d9028a
--- /dev/null
+++ b/testsuite/tests/perf/compiler/genMatchingTest
@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+# Generate a module with N data types and instances
+DEFS=10000
+MATCHES=500
+MODE=$1
+echo "module Defs where" > Defs.hs;
+for i in $(seq -w 1 $DEFS); do
+  echo "data T$i a = T$i a deriving Show" >> Defs.hs;
+done
+
+echo "{-# LANGUAGE TypeFamilies #-}" > Match.hs
+echo "{-# LANGUAGE StandaloneDeriving #-}" >> Match.hs
+echo "{-# LANGUAGE EmptyDataDecls #-}" >> Match.hs
+echo "module Match where" >> Match.hs
+echo "import Defs" >> Match.hs
+
+if [ $MODE -eq 0 ]; then
+  for i in $(seq -w 1 $MATCHES); do
+    echo "type family F$i a where" >> Match.hs;
+  done
+  echo "data T a = T" >> Match.hs
+  for i in $(seq -w 1 $MATCHES); do
+    echo "       (F$i a)" >> Match.hs;
+  done
+  echo "deriving instance Show (T a)" >> Match.hs;
+fi
+#elif [ $MODE -eq 1 ]; then
+#  echo "data T " >> Match.hs
+#    for i in $(seq -w 1 $MATCHES); do
+#      echo "       a$i" >> Match.hs;
+#    done
+#    echo "       = T " >> Match.hs
+#    for i in $(seq -w 1 $MATCHES); do
+#      echo "       a$i" >> Match.hs;
+#    done
+#    echo "deriving instance Show (T" >> Match.hs
+#    for i in $(seq -w 1 $MATCHES); do
+#      echo "       a$i" >> Match.hs;
+#    done
+#    echo "    )" >> Match.hs;
+#else
+#  for i in $(seq -w 1 $MATCHES); do
+#    echo "data F$i a" >> Match.hs;
+#  done
+#  echo "data T a = T" >> Match.hs
+#  for i in $(seq -w 1 $MATCHES); do
+#    echo "       (F$i a)" >> Match.hs;
+#  done
+#  echo "deriving instance Show (T a)" >> Match.hs;
+#
+#fi
+