GitLab

Simon Jakobi pushed to branch wip/sjakobi/T27653 at Glasgow Haskell Compiler / GHC

Commits:

218d6445

by Simon Jakobi at 2026-08-13T11:52:41+02:00

testsuite: Migrate perf tests off collect_compiler_stats('all')

The 'all' metric argument applies a single tolerance to bytes
allocated, max_bytes_used and peak_megabytes_allocated, although their
noise profiles are incompatible (#27653): allocations are nearly
deterministic, residency needs 10-20%, and peak is quantized to 1 MB.
Any single tolerance is too tight for one metric or too slack for
another. This migrates all users of 'all' (and of the 'all' default)
to explicit per-metric collection, ahead of removing 'all' from the
driver.

peak_megabytes_allocated is dropped everywhere: its 1 MB granularity
makes tight relative windows meaningless (#27613), and it is sensitive
to GC timing. In #27489 it drifted by -5.3% while max_bytes_used moved
by less than 0.1%. Where a test guards a memory property,
max_bytes_used covers it at byte granularity.

Where the motivating ticket was about compile-time memory
(T11545, T15304, T26425, LinkableUsage01/02), residency remains
gated via max_bytes_used, now with a residency-appropriate tolerance.

max_bytes_used is dropped where residency was only ever an accident of
'all':

* T15630, T15630a, T20261: the underlying tickets (#15630, #20261)
  contain no memory data at all. One is a simplifier-ticks blowup and
  the other is stated entirely in allocation numbers, so the 20%
  window never had teeth.

* T21839c: #21839's measurements show residency essentially flat
  (+0.16%) while allocations moved +7%, so allocations are the
  discriminating metric. They are already gated at 1% via
  collect_compiler_runtime. The ghc/max gate had previously broken CI
  spuriously (9fd11585eb widened it from 1% to 10% for that reason).

Allocation tolerances are tightened to the testsuite's conventional 2%
where 'all' previously left them at 10-20%.

Assisted-by: Claude Fable 5

2e568d97

by Simon Jakobi at 2026-08-13T12:05:11+02:00

testsuite: Remove the 'all' metric argument of collect_stats

'all' gated bytes allocated, max_bytes_used and peak_megabytes_allocated
at a single tolerance, although their noise profiles are incompatible,
making such tests either flaky or toothless (#27653).

Assisted-by: Claude Fable 5

8e164679

by Simon Jakobi at 2026-08-13T12:06:47+02:00

testsuite: Make the deviation argument of collect_stats mandatory

Almost every caller passes an explicit tolerance matched to the
metric's noise profile, and the silent 20% default is far slacker than
'bytes allocated' merits. Only two tests relied on it. They now state
their tolerance explicitly:

large-project gets 10%, in line with other large compile-time tests.

T9848 gets 2%: its metric is byte-for-byte deterministic across CI
jobs and platforms of a given test_env, has drifted only about 2.5%
since 2015, and the fusion failure it guards against would show up as
a roughly +30000% jump.

Assisted-by: Claude Fable 5

7 changed files:

libraries/base/tests/all.T
testsuite/driver/README.md
testsuite/driver/testlib.py
testsuite/tests/bytecode/TLinkable/all.T
testsuite/tests/perf/compiler/all.T
testsuite/tests/perf/compiler/large-project/all.T
testsuite/tests/perf/space_leaks/all.T

Changes:

libraries/base/tests/all.T

@@ -243,7 +243,7 @@ test('T8684', expect_broken(8684), compile_and_run, [''])
  test('hWaitForInput-accurate-stdin', [js_broken(22349), expect_broken_for(16535, threaded_ways), req_process], compile_and_run, [''])
  test('T9826',normal, compile_and_run,[''])
  test('T9848',
 -        [ collect_stats('bytes allocated')
 +        [ collect_stats('bytes allocated', 2)
          , only_ways(['normal'])
          , js_broken(22261)
          ],

testsuite/driver/README.md

@@ -35,11 +35,13 @@ differences, and things such as that are not necessary to be considered by the
  test writer anymore. This is due to the fact that the test comparison relies
  entirely on locally collected metrics on the testing machine.
 -As such, it is perfectly sufficient to write `collect_stats('all',20)` in the
 -".T" files to measure the 3 potential stats that can be collected for that test
 -and automatically test them for regressions, failing if there is more than a 20%
 -change in any direction. In fact, even that is not necessary as
 -`collect_stats()` defaults to 'all', and 20% deviation allowed.
 +A test states which metric to measure and how much deviation to allow, e.g.
 +`collect_stats('bytes allocated', 2)` in the ".T" files. Such a test fails if
 +the metric changes by more than 2% in either direction. To gate several metrics,
 +use one `collect_stats` call per metric, so that each gets a tolerance matched
 +to its noise profile: allocations are nearly deterministic and support tight
 +windows, while the residency metrics need considerably slacker ones (see
 +Note [Measuring residency] in testlib.py).
  The function `collect_compiler_stats()` is completely equivalent in every way to
  `collect_stats` except that it measures the performance of the compiler itself

testsuite/driver/testlib.py

@@ -24,7 +24,7 @@ import subprocess
  from testglobals import config, ghc_env, default_testopts, brokens, t, \
                          TestRun, TestResult, TestOptions, PerfMetric
  from testutil import strip_quotes, lndir, link_or_copy_file, passed, \
 -                     failBecause, testing_metrics, residency_testing_metrics, \
 +                     failBecause, residency_testing_metrics, \
                       stable_perf_counters, \
                       PassFail, badResult, str_warn, str_removeprefix
  from term_color import Color, colored
@@ -816,28 +816,20 @@ def _collect_generic_stat(name : TestName, opts, metric_infos):
  # -----
 -# Defaults to "test everything, and only break on extreme cases"
 -#
 -# The inputs to this function are slightly interesting:
 -# metric can be either:
 -#     - 'all', in which case all 3 possible metrics are collected and compared.
 -#     - The specific metric one wants to use in the test.
 -#     - A set of the metrics one wants to use in the test.
 -#
 -# Deviation defaults to 20% because the goal is correctness over performance.
 -# The testsuite should avoid breaking when there is not an actual error.
 -# Instead, the testsuite should notify of regressions in a non-breaking manner.
 +# metric is either a single metric name or a set of metric names. Use one
 +# call per metric so each gets a tolerance matched to its noise profile.
 +# See Note [Measuring residency] for the residency metrics.
+ #
  # collect_compiler_stats is used when the metrics collected are about the compiler.
  # collect_stats is used in the majority case when the metrics to be collected
  # are about the performance of the runtime code generated by the compiler.
 -def collect_compiler_stats(metric='all',deviation=20):
 +def collect_compiler_stats(metric, deviation):
      def f(name, opts, m=metric, d=deviation):
          no_lint(name, opts)
          return _collect_stats(name, opts, m, d, None, True)
      return f
 -def collect_stats(metric='all', deviation=20, static_stats_file=None):
 +def collect_stats(metric, deviation, static_stats_file=None):
      return lambda name, opts, m=metric, d=deviation, s=static_stats_file: _collect_stats(name, opts, m, d, s)
  def statsFile(comp_test: bool, name: str) -> str:
@@ -864,12 +856,9 @@ def _collect_stats(name: TestName, opts, metrics, deviation: Optional[int],
          # This is a bit weird, though.
          return
 -    # Normalize metrics to a list of strings.
 +    # Normalize metrics to a set of strings.
      if isinstance(metrics, str):
 -        if metrics == 'all':
 -            metrics = testing_metrics()
 -        else:
 -            metrics = { metrics }
 +        metrics = { metrics }
      opts.is_stats_test = True
      if is_compiler_stats_test:

testsuite/tests/bytecode/TLinkable/all.T

@@ -3,7 +3,8 @@
  # after they have been loaded into the `LoaderState`.
  # However, this property is currently not validated automatically.
  test('LinkableUsage01'
 -    , [ collect_compiler_stats('all', 2)
 +    , [ collect_compiler_stats('bytes allocated', 2)
 +      , collect_compiler_stats('max_bytes_used', 5)
        , extra_files(['genLinkables.sh', 'BCOTemplate.hs'])
        , pre_cmd('$MAKE -s --no-print-directory LinkableUsage01_Prep')
        , req_bco
@@ -18,7 +19,8 @@ test('LinkableUsage01'
  # Performance test for bytecode `Linkable`s.
  test('LinkableUsage02'
 -    , [ collect_compiler_stats('all', 2)
 +    , [ collect_compiler_stats('bytes allocated', 2)
 +      , collect_compiler_stats('max_bytes_used', 5)
        , extra_files(['genLinkables.sh', 'BCOTemplate.hs'])
        , pre_cmd('$MAKE -s --no-print-directory LinkableUsage02_Prep')
        , req_bco

testsuite/tests/perf/compiler/all.T

@@ -640,13 +640,16 @@ test ('T15164',
        ],
        compile,
        ['-v0 -O'])
 +# T15630/T15630a guard against exponential simplifier blowup when inlining
 +# join points (#15630). T15630a is a monomorphic variant that has blown up
 +# even when T15630 was fine; see the comment in T15630.hs.
  test('T15630',
 -      [collect_compiler_stats()
 +      [collect_compiler_stats('bytes allocated', 2)
        ],
        compile,
        ['-O2'])
  test('T15630a',
 -      [collect_compiler_stats()
 +      [collect_compiler_stats('bytes allocated', 2)
        ],
        compile,
        ['-O2'])
@@ -770,12 +773,19 @@ test ('T9198',
        compile,
        [''])
 +# Guards against quadratic demand-analysis cost on wide recursive data
 +# types, which manifested as a compile-time memory blowup (#11545).
  test('T11545',
 -     [ collect_compiler_stats('all', 15) ],
 +     [ collect_compiler_stats('bytes allocated', 2)
 +     , collect_compiler_residency(15) ],
       compile, ['-O'])
 +# Guards against the compile-time memory blowup of #15304, caused by
 +# over-keen inlining and demand-analysis memory usage on a module with
 +# many wide strict constructors.
  test('T15304',
 -     [ collect_compiler_stats('all', 10) ],
 +     [ collect_compiler_stats('bytes allocated', 2)
 +     , collect_compiler_residency(10) ],
       compile, ['-O'])
  test ('T20049',
        [ collect_compiler_stats('bytes allocated',2) ],
@@ -797,8 +807,10 @@ test('T16875',  # Testing one hole-fit with a lot in scope for #16875
       collect_compiler_runtime(4),
       compile, ['-fdefer-type-errors -fno-max-valid-hole-fits -package ghc'])
 +# Guards against renamer/typechecker allocation regressions on very large
 +# generated modules (#20261, a Happy-generated parser).
  test ('T20261',
 -      [collect_compiler_stats('all')],
 +      [collect_compiler_stats('bytes allocated', 2)],
        compile,
        [''])
@@ -807,8 +819,7 @@ test ('T20261',
  # does not sensibly handle one test acting as both
  # a compile-time and a run-time performance test
  test('T21839c',
 -    [   collect_compiler_stats('all', 10),
 -        collect_compiler_runtime(1),
 +    [   collect_compiler_runtime(1),
          only_ways(['normal'])],
      compile,
      ['-O'])
@@ -874,8 +885,12 @@ test('interpreter_steplocal',
       ghci_script,
       ['interpreter_steplocal.script'])
 +# Guards against the compile-time memory blowup of #26425; primarily
 +# stresses OccAnal and unfolding performance on a long chain of nested
 +# join points and cases.
  test ('T26425',
 -      [ collect_compiler_stats('all',20) ],
 +      [ collect_compiler_stats('bytes allocated', 2)
 +      , collect_compiler_residency(20) ],
        compile,
        ['-O'])

testsuite/tests/perf/compiler/large-project/all.T

@@ -7,7 +7,7 @@ def large_project_makedepend(num):
      return test(
          f'large-project-makedepend-{num}',
+         [
 -            collect_compiler_stats('bytes allocated'),
 +            collect_compiler_stats('bytes allocated', 10),
              pre_cmd(f'./large-project.sh {num}'),
              extra_files(['large-project.sh']),
              ignore_stderr,

testsuite/tests/perf/space_leaks/all.T

  setTestOpts(js_skip)
  test('space_leak_001',
 -     # This could potentially be replaced with
 -     # collect_stats('all',5) to test all 3 with
 -     # 5% possible deviation.
       [ collect_stats('bytes allocated',5),
        collect_runtime_residency(15),
        omit_ways(['profasm','profthreaded','threaded1','threaded2',