[LLVMdev] TSVC/Equivalencing-dbl

Hal Finkel hfinkel at anl.gov
Fri Oct 5 11:32:33 PDT 2012

----- Original Message -----
> From: "Duncan Sands" <duncan.sands at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: llvmdev at cs.uiuc.edu
> Sent: Friday, October 5, 2012 12:10:03 PM
> Subject: Re: TSVC/Equivalencing-dbl
> Oops, I ran the testsuite wrong: read clang output for dragonegg
> output.

Okay, can you resummarize? Do you mean that?

gcc -O0:
S1421         0.00                 16000

gcc -O0 under valgrind:
S1421         0.00                 17208.404325315

S1421    0.00           17208.404325315

This is all on Darwin, right?

I would certainly tend to suspect an 80-bit-intermediate issue, but, both gcc and clang give 16000 on PowerPC (which has no 80-bit). It could be a rounding issue, but would Darwin really have a different default rounding mode?

The computation being performed here is [in s1421() in tsc.inc]:
                for (int i = 0; i < LEN/2; i++) {
                        b[i] = xx[i] + a[i];
So *if* we're adding up the same numbers in the same order, the answer should be the same everywhere ;) Can you put in some print statements and confirm?

Thanks again,


Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory

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