Re: [PATCH] options: Save and restore opts_set for Optimization and Target options

[Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>]

On Wed, Sep 30, 2020 at 11:32:55AM +0200, Jakub Jelinek wrote:
> On Mon, Sep 28, 2020 at 09:50:00PM +0200, Stefan Schulze Frielinghaus via Gcc-patches wrote:
> > This patch breaks quite a view test cases (target-attribute/tattr-*) on
> > IBM Z.  Having a look at function cl_target_option_restore reveals that
> > some members of opts_set are reduced to 1 or 0 depending on whether a
> > member was set before or not, e.g. for target_flags we have
> 
> I've tried to reproduce the tattr FAILs reported in
> https://gcc.gnu.org/pipermail/gcc-testresults/2020-September/608760.html
> in a cross-compiler (with
> #define HAVE_AS_MACHINE_MACHINEMODE 1
> ), but couldn't, neither the ICEs nor the scan-assembler failures.
> Anyway, could you do a side-by-side debugging of one of those failures
> before/after my change and see what behaves differently?

I think the problem boils down that on S/390 we distinguish between four
states of a flag: explicitely set to yes/no and implicitely set to
yes/no.  If set explicitely, the option wins.  For example, the options
`-march=z10 -mhtm` should enable the hardware transactional memory
option although z10 does not have one.  In the past if a flag was set or
not explicitely was encoded into opts_set->x_target_flags ... for each
flag individually, e.g. TARGET_OPT_HTM_P (opts_set->x_target_flags) was
used.  This has changed with the mentioned patch in the sense that
opts_set encodes whether any flag of x_target_flags was set or not but
not which individual one after a call to the generated function
cl_target_option_restore where we have:
opts_set->x_target_flags = (mask & 1) != 0;

Compiling the following program

#pragma GCC target ("arch=z10")
void fn_pragma_0 (void) { }

with options `-march=z13 -mzarch -mhtm -mdebug` produces different flags
for 4ac7b669580 (commit prior your patch) and ba948b37768 (your patch).

This is my current understanding of the option handling.  I will try to
come up with a trace where these things become hopefully more clear.

Cheers,
Stefan