I did some experiments over the weekend and I discovered the flaw in my approach to address the differences in code generated during register allocation which are due to differences in FP calculations.
Initially I attempted to reduce the differences in FP calculations using the default compilation modes when compiling 32 and 64 bit. This was a mistake since trying to get calculations done using the X87 FP stack instructions when compiling -m32 to closely match those done by SSE2 instructions (-m64 default) may be a hopeless cause. I discovered over the weekend that the key change that reduces the differences in FP calculations was the change to build the X8664 compiler compiled 32-bits with "-mfpmath=sse -msse2" when using GCC. Thus the changes needed to address these issues are much simpler (the patches are attached). Sorry for the confusion on my part. Also I filed a bug on the issue: https://bugs.open64.net/show_bug.cgi?id=1005 Note that attached to the bug report is a script to build all 4 versions of the X8664 compiler. The test example is h264ref from SPEC 2006. Also there is a script that can be used to build a SPEC benchmark with all 4 versions of the compiler and compares the generated assembly files. Could a gatekeeper review these changes when they have the chance? Thanks, Doug > -----Original Message----- > From: Sun Chan [mailto:sun.c...@gmail.com] > Sent: Saturday, August 04, 2012 2:31 PM > To: Gilmore, Doug > Cc: "C. Bergström"; open64-devel > Subject: Re: [Open64-devel] Review request: fixing issues when building > the compiler as 64-bit binaries > > my point is, even these kind of "comparison" error due to rounding etc > should not have cause your heuristics to go haywire. If your > heuristics is so sensitive, something else is wrong. If you can > illustrate with an example, that might be good. For the kind of > heuristics I have seen, they don't matter. > Sun > > On Sun, Aug 5, 2012 at 1:58 AM, Gilmore, Doug <doug.gilm...@amd.com> > wrote: > > I was looking into other issues yesterday so I was sidetracked. > >> -----Original Message----- > >> From: Sun Chan [mailto:sun.c...@gmail.com] > >> Sent: Saturday, August 04, 2012 3:24 AM > >> To: Gilmore, Doug > >> Cc: "C. Bergström"; open64-devel > >> Subject: Re: [Open64-devel] Review request: fixing issues when > building > >> the compiler as 64-bit binaries > >> > >> I haven't had any real code segment to explain why the change to > float > >> to double is needed for the claim, i.e. enable 64bit porting, and > >> better precision. I have to do this in the abstract. > >> I don't see any relationship between float and double to 64 bit > >> porting. As for precision, the example given is "probability". For > >> compiler optimization, it is true that probability is widely used to > >> help heuristics, but I have yet to see an example where one needs > >> beyond 2 decimal point precision. > > If actually had 2 decimal point precision float point arithmetic, > then > > you would need to be extremely careful to insure that there were no > > reordering of FP operations. Otherwise there would be enough noise > in > > the calculations to produce different FP comparison results. > > > > I am still collecting data on this. > > > > Sorry for the delay. > > > > Doug > >> I'm gonna have to say, this change from float to double is not > useful > >> other than making data size larger, which is in general not a good > >> thing. > >> Sun > >> > >> On Fri, Aug 3, 2012 at 7:38 AM, Sun Chan <sun.c...@gmail.com> wrote: > >> > for the float/double issue, can you include a code snippet that > will > >> > affect by this change (you have mentioned probability, for > example) > >> > Thx! > >> > Sun > >> >
0001-Changed-a-test-in-INTERFERE_MGR-Create_End.patch
Description: 0001-Changed-a-test-in-INTERFERE_MGR-Create_End.patch
0002-X8664-m32-FP-compilation-mode-change-when-compiling-.patch
Description: 0002-X8664-m32-FP-compilation-mode-change-when-compiling-.patch
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