If memory serves, there are primops for converting between unboxed values of different widths.
Certainly converting between a float and a non-float will require an instruction on some architectures, since they use different register sets.
Re (2) I have no idea. You'll need to get more information... pprTrace or something.
Simon
| -----Original Message-----
| From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Ömer
| Sinan Agacan
| Sent: 06 December 2015 18:25
| To: ghc-devs
| Subject: question about coercions between primitive types in STG level
|
| Hi all,
|
| In my compiler pass(D1559, see ElimUbxSums.hs) I'm doing some unsafe
| coercions at the STG level. It works fine for lifted types, but for
| unlifted ones I'm having some problems. What I'm trying to do is given
| a number of primitive types I'm finding the one with biggest size, and
| then generating a constructor that takes this biggest primitive type
| as argument.
|
| The problem is that this is not working very well - GHC is generating
| illegal instructions that try to load a F32 value to a register
| allocated for I64, using movss instruction.
|
| CoreLint is catching this error and printing this:
|
| Cmm lint error:
| in basic block c1hF
| in assignment:
| _g16W::I64 = 4.5 :: W32; // CmmAssign
| Reg ty: I64
| Rhs ty: F32
|
| So I have two questions about this:
|
| 1. Is there a way to safely do this? What are my options here? What
| I'm trying
| to do is to use a single data constructor field for different
| primitive
| types. The field is guaranteed to be as big as necessary.
|
| 2. In the Cmm code shown above, the type annotation is showing `W32`
| but in the
| error message it says `F32`. I'm confused about this, is this error
| message
| given because the sizes don't match? (64bits vs 32bits) Why the
| type
| annotation says W32 while the value has type F32?
|
| Thanks..
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