panic when compiling SHA

[Simon Peyton-Jones]

| Note that removing the flag isn't a "solution" to the underlying problem
| of the intermediate code being awful. Switching to the linear allocator
| just permits compilation of core code that was worse than before. Now it
| needs to spill more registers when compiling the same source code.

In what way is the intermediate code awful? How could it be fixed?

Worth opening a ticket for that issue?  At the moment it's invisible because the issue appears superficially to be about register allocation.

Simon


| -----Original Message-----
| From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Ben
| Lippmeier
| Sent: 05 January 2014 10:47
| To: Kazu Yamamoto (山本和彦)
| Cc: ghc-devs at haskell.org
| Subject: Re: panic when compiling SHA
| 
| 
| On 04/01/2014, at 23:22 , Kazu Yamamoto (山本和彦) <kazu at iij.ad.jp>
| wrote:
| 
| > Hi,
| >
| >>> There are only a fixed number of register spill slots, and when
| >>> they're all used the compiler can't dynamically allocate more of
| >>> them.
| >>
| >> Not true any more in 7.8+ with the linear allocator.  I think it
| >> might still be true for the graph allocator, which is sadly suffering
| >> from a little bitrot and probably doesn't generate very good code
| >> with the new code generator.
| >>
| >> So, avoiding -fregs-graph should work around this with 7.8.
| >
| > I confirmed that removing -fregs-graph should work around this with
| > 7.8.
| 
| Ok, my mistake. We originally added -fregs-graph when compiling that
| module because both allocators had a fixed stack size, but the graph
| allocator did a better job of allocation and avoided overflowing the
| stack.
| 
| Note that removing the flag isn't a "solution" to the underlying problem
| of the intermediate code being awful. Switching to the linear allocator
| just permits compilation of core code that was worse than before. Now it
| needs to spill more registers when compiling the same source code.
| 
| Ben.
| 
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