id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
2756	state hack causes unneeded value to be evaluated	int-e	igloo	"The following code prints ""{{{Main: Why?}}}"" when compiled with {{{ghc -O1}}}. With {{{-fno-state-hack}}} it works fine.

{{{
data X = X ()

{-# NOINLINE newX #-}
newX :: () -> IO X
newX n = do
    let {-# NOINLINE value #-}
        value = n
    return (X value)

main = do
    x <- newX (error ""Why?"")
    case x of
        X _ -> return ()
}}}

Both pragmas are needed to exhibit the bug.

(In my actual code, {{{value}}} is an {{{unsafePerformIO}}} -- this was the motivation for adding the pragmas.)"	merge	closed	normal	6.10.2	Compiler	6.10.1	fixed			Unknown/Multiple	Unknown/Multiple		Unknown	simplCore/should_run/T2756