testsuite: Add performance test for #14766

This distills the essence of the Sigs.hs program found in the ticket.

testsuite/tests/perf/compiler/all.T

@@ -585,6 +585,13 @@ test ('T13253-spj',
       ],
       compile,
       ['-v0 -O'])
+test ('T14766',
+      [ collect_compiler_stats('bytes allocated',2),
+        pre_cmd('python3 genT14766.py > T14766.hs'),
+        extra_files(['genT14766.py']),
+      ],
+      compile,
+      ['-v0'])
 test ('T18223',
       [ collect_compiler_stats('bytes allocated',2)
       , compile_timeout_multiplier(2)

testsuite/tests/perf/compiler/genT14766.py

+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+N_VARS = 100
+N_BINDS = 50
+
+tyvars = ' '.join('v{i}'.format(i=i) for i in range(N_VARS))
+
+print('''
+{{-# LANGUAGE PartialTypeSignatures #-}}
+{{-# OPTIONS_GHC -Wno-partial-type-signatures #-}}
+
+module T14766 where
+
+newtype T {tyvars} = T ()
+
+'''.format(tyvars=tyvars))
+
+holes = ' '.join('_' for i in range(N_VARS))
+for i in range(N_BINDS):
+    print('v{i} :: T {holes}'.format(i=i, holes=holes))
+    print('v{i} = T ()'.format(i=i))
+
+