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Re: x86 regression: optimizer bug in 1.1 and dev
- To: Mumit Khan <khan at xraylith dot wisc dot edu>
- Subject: Re: x86 regression: optimizer bug in 1.1 and dev
- From: Toon Moene <toon at moene dot indiv dot nluug dot nl>
- Date: Tue, 10 Nov 98 23:42:06 +0100
- Cc: law at cygnus dot com, egcs-bugs at cygnus dot com
- Organization: Moene Computational Physics, Maartensdijk, The Netherlands
- References: <9811100808.AA14890@modi.xraylith.wisc.edu>
>> Excess precision on x86 issue I suspect.
>>
>> -ffloat-store makes it go away.
>>
> I completely forgot about this little gem.
>
> Is this something that we should always be adding to our
> compile flags on x86?
No, because:
1. It generates slower code.
2. It isn't correct in more convoluted examples anyway.
The bottom line, which I have repeated on comp.arch and
comp.compilers, is: Unless you don't use floating point registers
*at all*, reasonable floating point behaviour on the ix86
architecture is impossible.
[ There's a processor specific flag you can set prior to the main
program executing, but it'll only restrict floating point arithmetic
to double precision for the mantissa - the range of the exponent is
still the 80-bit variant one ]
Cheers,
Toon.