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Re: i686 (PentiumPro) Optimizer Bug


On Mon, Nov 16, 1998 at 10:15:43AM -0600, Robert Lipe wrote:
> I was unable to duplicate this problem with either 1.0.2 (as shipped
> with redhad 5.1) or with a Linux snapshot of egcs-2.92.21.
> 
> Interestingly, on 1.1.1, this example emits an opcode the OpenServer
> assembler cannot grok.  It seems to choke on:
> 
> 	/usr/tmp/cc2QneXL.s:35:unknown instruction: fcmove
> 	/usr/tmp/cc2QneXL.s:58:unknown instruction: fcmove

fcmove is a PPro/PII specific instruction: Float conditional move. (There's
also a non-float variant.)
It saves a conditional branch and is therefore used by the optimizer when
compiling w/ march=pentiumpro. Obviously, something's wrong with it ...

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|  cand.phys. Kurt Garloff        C1-O4-101 (Chemiegeb"aude)   |
|Lehrstuhl Hochfrequenztechnik  (Fakult"at f"ur Elektrotechnik)|
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