Commentary Cmm page (Observations and Areas for Improvement)
simonmarhaskell at gmail.com
Wed Nov 29 03:35:22 EST 2006
Peter Tanski wrote:
> On Nov 24, 2006, at 2:50 AM, Simon Peyton-Jones wrote:
>> Peter Tanski wrote:
>>> I was trying to determine the grounds for when a side-effecting
>>> primop would be inlined and when it would be coded as a separate
>> That's a matter for the implementation, not the C--, or Cmm,
>> specification. The user should not care. The implementer makes the
>> usual cost/performance/complexity trade-off, and decides. I think
>> there is no more to it than that.
> Quite so. The wiki is intended for implementers, in this case those
> who would be interested in implementing new Cmm primitive operators.
>> If you are asking what GHC's current code-generator's decisions are,
>> concerning this choice, I couldn't tell you without looking at the code!
> According to nativeGen/MachCodeGen.hs, out-of-line primitive operators
> (usually floating point operations) seem to be foreign calls. I
> suppose a possible addition to Cmm, such as primitive operators with
> exceptions, might be inlined but I haven't looked carefully at the
Floating point PrimOps (eg. sinFloat#) are compiled into
CmmForeignCall (CmmPrim MO_F32_Sin) ...
which the NCG can choose to compile to either a foreign call or an inline
instruction sequence. On x86 (using the x87 instruction set) some of these are
compiled into inline instructions; on x86_64 (using SSE2 for floating point)
they all turn into foriegn calls.
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