Hi,

With Hongtao's help (thanks), we got the SPEC2017 performance
evaluation result on x86_64 (see [1]), this new parameter
ira-consider-dup-in-all-alts has negative effects on i386.
Since we observed it can benefit ports aarch64 and rs6000, the
param is set as 1 by default, this patch is to disable it on
i386 explicitly to avoid performance degradation there.

Bootstrapped & regtested on x86_64-redhat-linux.

Is it ok for trunk?

BR,
Kewen

[1] https://gcc.gnu.org/pipermail/gcc-patches/2021-June/573986.html
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