#5256: code in an "else" branch that is never executed still does influence
runtime (Vectorizer?)
-------------------------------+--------------------------------------------
Reporter: j.waldmann | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: None/Unknown
-------------------------------+--------------------------------------------
Comment(by j.waldmann):
compile:
{{{
ghc -O2 -fforce-recomp -threaded -rtsopts bug.hs
}}}
run: (with "id")
{{{
./bug 10000000 +RTS -N1
("numCap",1)
5000000
sum xs 0.250303s
(5000000,5000000)
foldb_cap 0.318648s
(5000000,5000000)
foldl' 0.026361s
}}}
run (with "undefined")
{{{
./bug 10000000 +RTS -N1
("numCap",1)
5000000
sum xs 0.246084s
(5000000,5000000)
foldb_cap 0.03731s
(5000000,5000000)
foldl' 0.02679s
}}}
notice the drop from 0.3 s to 0.04 s
{{{
ghc --info
[("Project name","The Glorious Glasgow Haskell Compilation System")
,("Project version","7.0.3")
,("Booter version","6.12.1")
,("Stage","2")
,("Build platform","x86_64-unknown-linux")
,("Host platform","x86_64-unknown-linux")
,("Target platform","x86_64-unknown-linux")
,("Have interpreter","YES")
,("Object splitting","YES")
,("Have native code generator","YES")
,("Have llvm code generator","YES")
,("Support SMP","YES")
,("Unregisterised","NO")
,("Tables next to code","YES")
,("RTS ways","l debug thr thr_debug thr_l thr_p dyn debug_dyn thr_dyn
thr_debug_dyn")
,("Leading underscore","NO")
,("Debug on","False")
,("LibDir","/usr/local/lib/ghc-7.0.3")
,("Global Package DB","/usr/local/lib/ghc-7.0.3/package.conf.d")
,("C compiler flags","[\"-fno-stack-protector\"]")
,("Gcc Linker flags","[]")
,("Ld Linker flags","[]")
]
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5256#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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