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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000

On May 13, 2009, at 4:51 AM, Duncan Sands wrote:


Sorry, I missed to mention that I used an additional option -mpc64 for
32-bit GCC4.4. It is not possible to generate SPECFP2000 expected
results by GCC4.4 without this option. LLVM does not support this
option. And this option can significantly improve the performance. So
32-bit comparison of SPECFP2000 should be taken with a grain of salt.

what does -mpc64 do exactly? The gcc docs say:
`-mpc64' rounds the the significands of results of floating-point operations to 53 bits (double precision)
Does this mean that a rounding operation is performed after each fp
operation, or that optimizations are permitted that don't result in
accurate extended double precision values as long as they are correct
to 53 bits, or something else?

The LLVM code generators have an option called -limit-float-precision:
-limit-float-precision=<uint> - Generate low-precision inline sequences for some float libcalls
I'm not sure what it does exactly, but perhaps it is similar to - mpc64?

No, that inline a small set of libcalls into sequences code that implement low precision math (6, 8, 12 bits).




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