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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/46900] [4.6 Regression] 50% slowdown when linking with LTO in a single step
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46900

--- Comment #6 from Tobias Burnus <burnus at gcc dot gnu.org> 2010-12-16 15:23:40 UTC ---
I think that the files passed to lto1 are the same - but I get different
command-line options:


a) Two-step compile with "-fexternal-blas -flto -Ofast -march=native"

x86_64-unknown-linux-gnu/4.6.0/lto1 -march=k8-sse3 -msahf --param
l1-cache-size=64 --param l1-cache-line-size=64 --param l2-cache-size=1024
-mtune=k8


b) Single-step compile:

x86_64-unknown-linux-gnu/4.6.0/lto1 -quiet -dumpbase ccmRjX1L.ltrans0.o
-mtune=generic -march=x86-64


Thus, the "-march=native" somehow gets lost in the single-step compile.