Moritz I have this stuff all paged out. Would you like to give a couple of concrete examples of what you have in mind, with any design alternatives? And illustrate your suggestion about propagation, which I don't yet grok. Thanks Simon | -----Original Message----- | From: Moritz Angermann [mailto:moritz.angermann@gmail.com] | Sent: 06 October 2017 04:37 | To: Simon Peyton Jones | Cc: GHC developers | Subject: Re: In C--: should CmmCall and CmmProc agree on their live | registers? | | Hi Simon, | | no, I did not until now. Thank you! As such it is acceptable that the | CmmCalls set of live registers is a superset of the CmmProcs live registers | that is called. | | Say we shrink the set of live registers of the CmmProc, as we determine that | some of the arguments passed in registers are not used in the graph at all. | Would we want to propagate this information to the CmmCall if possible? | | Cheers, | Moritz | | | > On Oct 5, 2017, at 5:59 PM, Simon Peyton Jones | wrote: | > | > Did you ever get a reply to this? | > | > In the output of the codegen, CmmProcs should have no live registers apart | from those used to pass args, and the standard ones. | > | > Simon | > | > | -----Original Message----- | > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of | > | Moritz Angermann | > | Sent: 22 September 2017 07:33 | > | To: GHC developers | > | Subject: In C--: should CmmCall and CmmProc agree on their live | registers? | > | | > | Hi, | > | | > | apologies for writing so many emails recently. This is a minor | > | spinoff from the "The Curious Case of T6084" email. | > | | > | While digging into it, I keep asking myself if CmmProc’s live | > | registers should match those of the CmmCall that is calling it? | > | | > | Is there any invariant we try to enforce or would want to enforce? | > | | > | - Can the CmmProcs live registers be a strict superset of | > | the corresponding CmmCalls? | > | | > | From the source comments in `compiler/cmm/Cmm.hs`: | > | > Registers live on entry. Note that the set of live | > | > registers will be correct in generated C-- code, but | > | > not in hand-written C-- code. However, | > | > splitAtProcPoints calculates correct liveness | > | > information for CmmProcs. | > | | > | I would assume that this is an invalid case? | > | | > | - Can the CmmProcs live registers be a strict subset of | > | the corresponding CmmCalls? | > | | > | This case however seems to be valid case. However, this | > | makes me wonder if we can, and should(?) propagate the | > | live register info from the CmmProc to the CmmCall so | > | that they match up, and the registers are not kept live | > | at the origin of the CmmCall if they aren’t needed? And | > | as such potentially compute anything to put into the | > | registers the CmmCall considers live, but the CmmProc | > | would ignore anyway? | > | | > | Cheers, | > | Moritz | > | _______________________________________________ | > | ghc-devs mailing list | > | ghc-devs@haskell.org | > | | > | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmail | > | .haskell | > | .org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc- | > | | > | devs&data=02%7C01%7Csimonpj%40microsoft.com%7C6009bb0f47a447a4217708 | > | d50183ce | > | fa%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636416587981602708&s | > | data=vII | > | rlKVJa6E%2FBvVz5Sod1c544nw6gsGp54Mlhr7bQ8g%3D&reserved=0