Re: i370 port

["Paul Edwards" <mutazilah@gmail.com>]

> Why are you migrating to 3.4.6 now, instead of to a current version?
> If you want to include this in mainline some day, then eventually it
> has to be caught up - and 3.4.6 is older than it may appear from the
> release date, since it branched off of mainline five years ago.  A lot
> has changed since then.

A question about those changes.

One of the things that I experienced when porting 3.2.3 to MVS
was that GCC was sensitive to the exact floating point representation.

Register selection was different depending on those slight differences.

Below is what documentation I have for it.  Dave Edwards, who
wrote another S/370 emulator, was the one who discovered that.

Does anyone know if that was changed somewhere along the line?

BFN.  Paul.



17. The assembler code generated by gccmvs when run on the
PC is slightly different (even when the same parameters
are used for code generation) from that when run on the
mainframe, if -O2 is used instead of -Os. But functionally
equivalent. This non-deterministic nature of the compiler
is disconcerting. It seems to not always allocate registers
consistently. This has been traced to floating point code
in predict.c and local-alloc.c which is sensitive to the
very small changes in floating point representation. This
should be changed to include deltas when comparing floating
point values. Here's an example of what's happening:

*** c-lex.s Mon Jan 14 20:48:35 2008
--- temp.dat Mon Jan 14 21:14:04 2008
***************
*** 1328,1335 ****
           SLR   15,15
           STC   15,0(3,4)
           SLR   6,6
-          LR    9,6
           LR    8,6
           L     2,192(13)
           CLR   2,5
           BNL   L303
--- 1328,1335 ----
           SLR   15,15
           STC   15,0(3,4)
           SLR   6,6
           LR    8,6
+          LR    9,6
           L     2,192(13)
           CLR   2,5
           BNL   L303