https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81519
Bug ID: 81519
Summary: Enhancement: Add --help=target-distcc or similar to
dump clean, optimal CFLAGS without using -march=native
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: driver
Assignee: unassigned at gcc dot gnu.org
Reporter: daniel.santos at pobox dot com
Target Milestone: ---
To be clear, there is a working solution and that is to run a command such as
this:
gcc -v -E -x c -march=native -mtune=native - < /dev/null 2>&1 | grep cc1 | perl
-pe 's/^.* - //g;'
The problem is that it is very verbose and redundant. You can filter out the
-mno-* flags, but I'm not certain that that is always correct and still leaves
many more -m<extention> flags. Ideally, a command such as `gcc -Q -x c
-march=native --help=target-distcc' would emit something like
CFLAGS="-march=sandybridge --param l1-cache-size=32 --param
l1-cache-line-size=64 --param l2-cache-size=8192 -mtune=sandybridge"
In addition to the above, the output should contain any -m<extension> and
-mno-<extension> flags for each that actually differ from the arch and not
include extensions that are already included in another extension.
Calculating this from a script would actually be possible if bug #39851 were
fixed, but there is currently no (that I am aware of) way to get an output of
extensions each arch consists of. These extensions are listed in invoke.texi
by marketing name, but this would still be a parsing challenge and is subject
to human error since it isn't parsed from the backend code.
Alternatively, I presume that cleaning up the driver code to omit redundant
options could result in the first example being sufficient, but I don't
understand the implications of that and I suspect would likely break other
things.
