#7063: Register allocators can't handle non-uniform register sets
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Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.8.1
Component: Compiler (NCG) | Version: 7.4.2
Keywords: | Os: Unknown/Multiple
Architecture: x86 | Failure: Runtime performance bug
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Neither the linear scan register allocator nor the graph-colouring
allocator can properly handle the fact that some registers on x86 have 8
and 16-bit versions and some don't. We got away with this until now
because the only free registers on x86 were `%eax`, `%ecx` and `%edx`, but
now we can also treat `%esi` as free when it isn't being used for R1 (see
f857f0741515b9ebf186beb38fe64448de355817). However, `%esi` doesn't have
an 8-bit version, so we cannot treat it as allocatable because the
register allocator will try to use it when an 8-bit register is needed
(see 105754792adac0802a9a59b0df188b58fb53503f).
LLVM doesn't have this problem, so one workaround is to compile with
`-fllvm` to get the extra register(s) on x86.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7063>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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