On Mon, 12 Jun 2017, Richard Earnshaw (lists) wrote:
> It does. The problem seems to be a generic one in the driver in that
> the rewrite rules are always passed the first instance of -march and not
> the last. Indeed, with the aarch64 compiler, if I write
>
> gcc -mcpu=native -mcpu=cortex-a53
>
> then the driver will rewrite this as
>
> ./cc1 -mcpu=cortex-a53 -mcpu=<expansion of native cpu name>
>
> which doesn't seem to be the right thing at all.
>
> So we either have a generic problem with all option rewriting, or there
> are some subtle details of it that we've not figured out yet.
>
> Joseph, is there a way to get the rewrite rules to receive the *last*
> instance of a flag rather than the first? Or is the current behaviour
> simply wrong?
I think there are at least two separate issues here.
In the AArch64 port (and other ports), the specs for -mcpu=native use
%{mcpu=native:%<mcpu=native %:local_cpu_detect(cpu)} as part of
DRIVER_SELF_SPECS. Options added by DRIVER_SELF_SPECS are added at the
end of the command line (after OPTION_DEFAULT_SPECS has been processed).
Thus, if there is any -mcpu=native option, the options from generated by
local_cpu_detect will be added.
In patch 14 of this series, you have specs of the form %{mcpu=*: cpu %*}
inside a canon_arch call. According to the comment in gcc.c documenting
specs
%{S*:X} substitutes X if one or more switches whose names start
with -S was given to GCC. Normally X is substituted only
once, no matter how many such switches appeared. However,
if %* appears somewhere in X, then X will be substituted
once for each matching switch, with the %* replaced by the
part of that switch that matched the '*'. A space will be
appended after the last substition unless there is more
text in current sequence.
this ought to mean that every -mcpu= option results in a corresponding cpu
<something> in the arguments to canon_arch (in the same order as the
original options). If it doesn't, that sounds like a bug in the %*
handling.
Overridden options can be removed before specs processing if a cycle of
options is marked with Negative in the .opt files (see prune_options), but
that doesn't apply to options with arguments. If you had a system for
pruning e.g. all but the last -mcpu= option (for options where it's just
the last argument that matters), you'd also want to make sure that prior
options do still generate errors if the option argument is invalid.
--
Joseph S. Myers
[email protected]
