This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: basic asm and memory clobbers

On 11/23/2015 03:04 AM, Andrew Haley wrote:
On 21/11/15 12:56, David Wohlferd wrote:
So, what now?

While I'd like to take the big step and start kicking out warnings for
non-top-level right now, that may be too bold for phase 3.  A more
modest step for v6 would just provide a way to find them (maybe
something like -Wnon-top-basic-asm or -Wonly-top-basic-asm) and doc the
current behavior as well as the upcoming change.

Warnings would be good.

My warning still holds: there are modes of compilation on some
machines where you can't clobber all registers without causing reload
failures.  This is why Jeff didn't fix this in 1999.  So, if we really
do want to clobber "all" registers in basic asm it'll take a lot of
Exactly. In retrospect, I probably should have generated more tests for those conditions back in '99. Essentially they'd document a class of problems we'd like to fix over time.

I know some have been addressed in various forms, but it hasn't been systematic.

My recommendation here is to:

  1. Note in the docs what the behaviour should be.  This guides where
  we want to go from an implementation standpoint.  I think it'd be fine
  to *suggest* only using old style asms at the toplevel, but I'm less
  convinced that mandating that restriction is wise.

  2. As we come across failures for adhere to the desired behaviour,
  fix or document them as known inconsistencies.  If we find that some
  are inherently un-fixable, then we'll need to tighten the docs around

The more I think about it, I'm just not keen on forcing all those old-style asms to change.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]