diff options
Diffstat (limited to 'docs/users_guide/profiling.rst')
| -rw-r--r-- | docs/users_guide/profiling.rst | 38 |
1 files changed, 33 insertions, 5 deletions
diff --git a/docs/users_guide/profiling.rst b/docs/users_guide/profiling.rst index 418c9b0bb0..1c2f458f10 100644 --- a/docs/users_guide/profiling.rst +++ b/docs/users_guide/profiling.rst @@ -439,19 +439,47 @@ compiled program. details. .. ghc-flag:: -fprof-late - :shortdesc: Auto-add ``SCC``\\ s to all top level bindings *after* the optimizer has run. + :shortdesc: Auto-add ``SCC``\\ s to all top level bindings *after* the core pipeline has run. :type: dynamic :reverse: -fno-prof-late :category: :since: 9.4.1 - Adds an automatic ``SCC`` annotation to all top level bindings late in the core pipeline after - the optimizer has run. This means these cost centres will not interfere with core-level optimizations + Adds an automatic ``SCC`` annotation to all top level bindings late in the compilation pipeline after + the optimizer has run and unfoldings have been created. This means these cost centres will not interfere with core-level optimizations and the resulting profile will be closer to the performance profile of an optimized non-profiled executable. - While the results of this are generally very informative some of the compiler internal names - will leak into the profile. + While the results of this are generally informative, some of the compiler internal names + will leak into the profile. Further if a function is inlined into a use site it's costs will be counted against the + caller's cost center. + + For example if we have this code: + + .. code-block:: haskell + + {-# INLINE mysum #-} + mysum = sum + main = print $ mysum [1..9999999] + + Then ``mysum`` will not show up in the profile since it will be inlined into main and therefore + it's associated costs will be attributed to mains implicit cost centre. + +.. ghc-flag:: -fprof-late-inline + :shortdesc: Auto-add ``SCC``\\ s to all top level bindings *after* the optimizer has run and retain them when inlining. + :type: dynamic + :reverse: -fno-prof-late-inline + :category: + + :since: 9.4.1 + + Adds an automatic ``SCC`` annotation to all top level bindings late in the core pipeline after + the optimizer has run. This is the same as :ghc-flag:`-fprof-late` except that cost centers are included in some unfoldings. + + The result of which is that cost centers *can* inhibit core optimizations to some degree at use sites + after inlining. Further there can be significant overhead from cost centres added to small functions if they are inlined often. + + You can try this mode if :ghc-flag:`-fprof-late` results in a profile that's too hard to interpret. .. ghc-flag:: -fprof-cafs :shortdesc: Auto-add ``SCC``\\ s to all CAFs |