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Opened by dons@trac-dons

-fhpc inteferes/prevents rewrite rules from firing

Use case:

I'm writing tests for rewrite rules, and using HPC to determine if rules were fired (and their code exercised). HPC is quite cool here, since it lets us see which rules fired, without needing to explicitly export functions to test.

However, -fhpc seems to prevent many rules from firing (likely due to ticks getting in the way?)

For example:

import qualified  Data.ByteString.Char8 as C

main = print (C.pack "literal")

When compiled normally, triggers a nice rewrite rule:

$ ghc -O2 A.hs -ddump-rule-firings -c
Rule fired: unpack
Rule fired: Class op show
Rule fired: unpack-list
Rule fired: ByteString packChars/packAddress

Now with -fhpc:

$ ghc -O2 A.hs -ddump-rule-firings A.hs -c -fhpc
Rule fired: unpack
Rule fired: Class op show
Rule fired: unpack-list

What's the best way to ensure the same code is exercised with and without -fhpc here? (I'd quite like to get this working, since rewrite rules benefit from testing.)

Edited by thomie