[PATCH] PR85678: Change default to -fno-common

[Iain Sandoe]

Hi Wilco,

Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:

>> Testsuite fails are order “a few hundred” mostly seem to be related to tree-prof
>> and vector tests (plus the anticipated scan-asm stuff, where code-gen will have
>> changed).  I don’t have cycles to analyse the causes right now - but that gives
>> an idea.
> 
> Are those tests specific to Power? I got 14 failures in total across the full
> C and C++ test suites. Note it's easy to update the default options for a
> specific test directory if needed.

No, the test was on x86_64-darwin16 (m32/m64)  and a very rough estimate of the 
number of fails (but definitely in the hundreds, not tens) - I haven’t tried the same on
PPC; the h/w is tied up with gcc-7 backport testing.

the change for *-*-darwin* will be that the ABI mandates common items to be 
indirected, thus defaulting to no-common will have the effect of changing the
generated code - and it’s a fairly common pattern in the testsuite to have uninit globals.

 * I’d expect broken scan-asms (probably not difficult to fix, just tedious).
 * not sure why it seems to have a particularly adverse effect on the tree-prof stuff.

short on cycles in the run up to stage #1 end + gcc-7 release .. but will try to 
poke at it over the next few days.

cheers
Iain