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Diffstat (limited to 'docs/users_guide/debugging.rst')
| -rw-r--r-- | docs/users_guide/debugging.rst | 22 |
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diff --git a/docs/users_guide/debugging.rst b/docs/users_guide/debugging.rst index 83d093cd06..1a1791bbbd 100644 --- a/docs/users_guide/debugging.rst +++ b/docs/users_guide/debugging.rst @@ -111,6 +111,28 @@ Dumping out compiler intermediate structures Show allocation and runtime statistics for various stages of compilation. Allocations are measured in bytes. Timings are measured in milliseconds. +.. ghc-flag:: -ddump-make-stats + :shortdesc: Dump information about the project build time and build graph. + :type: dynamic + + Show some statistics about the project build graph after compilation has finished. + These can be useful identifying bottlenecks in your projects module structure. + + The statistics which are currently outputted are: + + * The modules which took longest to compile. + * The modules which have the largest "flow". The initial flow is 1, and split + evenly between all roots of the dependency graph. The flow is propagated + through the graph, accumulated on each node and split evenly on children. + The result is that any synchronisation points will have a flow equal to 1, + and likewise other important modules will have a high flow value. + * The length of the longest (critical) path through the project. This provides + a lower bound on the projects compilation time. + * The "parallelism score" which is the sum of compiling all nodes divided by + the length of the critical path. This should be a more stable metric then + critical path length because it doesn't depend on how fast your computer is. + + GHC is a large program consisting of a number of stages. You can tell GHC to dump information from various stages of compilation using the ``-ddump-⟨pass⟩`` flags listed below. Note that some of these tend to produce a lot of output. |