Adding -ffp-contract=off flag.
#266
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This is needed for floating point stability. The global placement depends on the output of the FFT library. Without `-ffp-contract=off` the current FFT library produces different results dependent on if the compiler is targeting an x86 architecture which has the "FMA instruction". The FMA instruction omits the rounding done in the multiplication instruction, making the calculations produce different results for some input values See https://kristerw.github.io/2021/11/09/fp-contract/ See also OpenROAD change @ The-OpenROAD-Project/OpenROAD#4518 Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>
QuantamHD
approved these changes
Jan 10, 2024
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Should this go in the bazelrc as a global option as well? |
Potentially, I don't know how that works? |
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You can add flags to the bazel command line by default so https://github.com/hdl/bazel_rules_hdl/blob/main/.bazelrc#L17 So something like |
This is needed for floating point stability. The global placement depends on the output of the FFT library. Without `-ffp-contract=off` the current FFT library produces different results dependent on if the compiler is targeting an x86 architecture which has the "FMA instruction". The FMA instruction omits the rounding done in the multiplication instruction, making the calculations produce different results for some input values See https://kristerw.github.io/2021/11/09/fp-contract/ See also OpenROAD change @ The-OpenROAD-Project/OpenROAD#4518 Signed-off-by: Tim Ansell <tansell@google.com>
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Looks good! |
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This is needed for floating point stability.
The global placement depends on the output of the FFT library. Without
-ffp-contract=offthe current FFT library produces different results dependent on if the compiler is targeting an x86 architecture which has the "FMA instruction".The FMA instruction omits the rounding done in the multiplication instruction, making the calculations produce different results for some input values
See https://kristerw.github.io/2021/11/09/fp-contract/
See also OpenROAD change @
The-OpenROAD-Project/OpenROAD#4518