Re: pre egcs-1.1 testing and Linux 2.1.x

Stephen R. van den Berg (srb@cuci.nl)
Mon, 24 Aug 1998 16:58:37 +0200

Andrea Arcangeli wrote:
>On Mon, 24 Aug 1998, Philip Blundell wrote:
>>I think it's more subtle than that. The bug is not in the optimisations per
>>se, it's in the register allocator and just happens to be provoked more often
>>by higher optimisation (particularly when regparm is in use, because that
>>increases register pressure significantly near function calls).

>Are you sure? Did you tried it in practice? I thought that was the RTL
>code generated by the optimization function (not arch dependent) that was
>buggy:

It's not quite that simple.

>GOOD RTL -> buggy optimization function -> BAD RTL
>The RTL is arch indipendent.

>As you say it could be also that:
>GOOD RTL -> not buggy optimization function -> GOOD RTL 2
>and that:

>GOOD RTL -> buggy asm generator -> GOOD ASM
>GOOD RTL 2 -> buggy asm generator -> BAD ASM

Actually what happens is:

GOOD RTL -> several optimisations -> GOOD RTL2
GOOD RTL2 -> convert from arch-indep to arch-dep register tags -> BAD RTL3
BAD RTL3 -> BAD ASM

If the first optimisation step is left out, the conversion from:
GOOD RTL -> GOOD RTL3
works without problems in most cases (even though the conversion itself
is buggy, but only sometimes).

-- 
Sincerely,                                                          srb@cuci.nl
           Stephen R. van den Berg (AKA BuGless).


This signature third word omitted, yet is comprehensible.


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