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[Bug target/57952] AVX/AVX2 no ymm registers used in a trivial reduction
- From: "jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 17 May 2017 13:25:45 +0000
- Subject: [Bug target/57952] AVX/AVX2 no ymm registers used in a trivial reduction
- Auto-submitted: auto-generated
- References: <bug-57952-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57952
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Why should there be any references to that? -march= is an ISA selection
option, it says the compiler may use the instructions from the ISA.
-ftree-vectorize is an optimization option (default at -O3 and -Ofast), which
attempts to vectorize loops using the selected ISA if possible. The reason it
isn't on at -O2 is that it doesn't always improve code, it can make code slower
as well, and usually makes the code larger; it really depends on the loop etc.