[GHC] #13904: LLVM does not need to trash caller-saved registers.

[GHC]

#13904: LLVM does not need to trash caller-saved registers.
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        Reporter:  kavon             |                Owner:  kavon
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  llvm, codegen
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #4992, #4308      |  Differential Rev(s):  Phab:D5190
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"adcb5fb47c0942671d409b940d8884daa9359ca4/ghc"
 adcb5fb4/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="adcb5fb47c0942671d409b940d8884daa9359ca4"
 Multiple fixes / improvements for LLVM backend

 - Fix for #13904 -- stop "trashing" callee-saved registers, since it is
   not actually doing anything useful.

 - Fix for #14251 -- fixes the calling convention for functions passing
   raw SSE-register values by adding padding as needed to get the values
   in the right registers. This problem cropped up when some args were
   unused an dropped from the live list.

 - Fixed a typo in 'readnone' attribute

 - Added 'lower-expect' pass to level 0 LLVM optimization passes to
   improve block layout in LLVM for stack checks, etc.

 Test Plan: `make test WAYS=optllvm` and `make test WAYS=llvm`

 Reviewers: bgamari, simonmar, angerman

 Reviewed By: angerman

 Subscribers: rwbarton, carter

 GHC Trac Issues: #13904, #14251

 Differential Revision: https://phabricator.haskell.org/D5190
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13904#comment:9>
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