Re: [PATCH GCC/03]New option warning missed optimization on loops whose counter may overflow

[Martin Jambor <mjambor at suse dot cz>]

On Thu, Jul 21, 2016 at 04:50:31PM +0000, Bin Cheng wrote:
> Hi,
> This patch adds new option -Wmissed-loop-optimizations warning on loops whose counter may overflow, as well as makes -Wunsafe-loop-optimizations an alias to the new option.
> Bootstrap and test on x86_64 ongoing.  Is it OK?

I'm repeating myself and since we already have a warning for this it
might make sense to continue having one, but shouldn't we be trying to
move towards the -fopt-info mechanism for optimization feedback?  We
already seem to have OPTGROUP_LOOP even, so could you perhaps consider
also adding a call to

dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc, text)

?

Thanks,

Martin

> 
> Thanks,
> bin
> 
> 2016-07-20  Bin Cheng  <bin.cheng@arm.com>
> 
> 	* common.opt (Wmissed-loop-optimizations): New option.
> 	(Wunsafe-loop-optimizations): Alias to Wmissed-loop-optimizations.
> 	* doc/invoke.texi (Wmissed-loop-optimizations): Ditto.
> 	(Wunsafe-loop-optimizations): Alias to Wmissed-loop-optimizations.
> 	* tree-ssa-loop-niter.c (number_of_iterations_exit): Use option
> 	Wmissed-loop-optimizations.

> diff --git a/gcc/common.opt b/gcc/common.opt
> index 8a292ed..3d62657 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -625,7 +625,12 @@ Common Var(warn_null_dereference) Warning
>  Warn if dereferencing a NULL pointer may lead to erroneous or undefined behavior.
>  
>  Wunsafe-loop-optimizations
> -Common Var(warn_unsafe_loop_optimizations) Warning
> +Common Alias(Wmissed-loop-optimizations)
> +Warn if the loop cannot be optimized due to nontrivial assumptions.
> +Same as -Wmissed-loop-optimizations.
> +
> +Wmissed-loop-optimizations
> +Common Var(warn_missed_loop_optimizations) Warning
>  Warn if the loop cannot be optimized due to nontrivial assumptions.
>  
>  Wmissing-noreturn
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 3041c18..5a2bb09 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -302,8 +302,8 @@ Objective-C and Objective-C++ Dialects}.
>  -Wswitch  -Wswitch-bool  -Wswitch-default  -Wswitch-enum @gol
>  -Wswitch-unreachable  -Wsync-nand @gol
>  -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
> --Wtype-limits  -Wundef @gol
> --Wuninitialized  -Wunknown-pragmas  -Wunsafe-loop-optimizations @gol
> +-Wtype-limits  -Wundef -Wuninitialized  -Wunknown-pragmas @gol
> +-Wmissed-loop-optimizations -Wunsafe-loop-optimizations @gol
>  -Wunsuffixed-float-constants  -Wunused  -Wunused-function @gol
>  -Wunused-label  -Wunused-local-typedefs -Wunused-parameter @gol
>  -Wno-unused-result -Wunused-value @gol -Wunused-variable @gol
> @@ -4990,9 +4990,14 @@ If the stack usage is (partly) dynamic and not bounded, it's:
>  @opindex Wunsafe-loop-optimizations
>  @opindex Wno-unsafe-loop-optimizations
>  Warn if the loop cannot be optimized because the compiler cannot
> -assume anything on the bounds of the loop indices.  With
> -@option{-funsafe-loop-optimizations} warn if the compiler makes
> -such assumptions.
> +assume anything on the bounds of the loop indices.  Same as
> +@option{-Wmissed-loop-optimizations}.
> +
> +@item -Wmissed-loop-optimizations
> +@opindex Wmissed-loop-optimizations
> +@opindex Wno-missed-loop-optimizations
> +Warn if the loop cannot be optimized because the compiler cannot
> +assume anything on the bounds of the loop indices.
>  
>  @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
>  @opindex Wno-pedantic-ms-format
> diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
> index 2061eafa..38b5552 100644
> --- a/gcc/tree-ssa-loop-niter.c
> +++ b/gcc/tree-ssa-loop-niter.c
> @@ -2333,7 +2333,7 @@ number_of_iterations_exit (struct loop *loop, edge exit,
>  
>        wording = N_("missed loop optimization, the loop counter may overflow");
>        warning_at ((LOCATION_LINE (loc) > 0) ? loc : input_location,
> -		  OPT_Wunsafe_loop_optimizations, "%s", gettext (wording));
> +		  OPT_Wmissed_loop_optimizations, "%s", gettext (wording));
>      }
>  
>    return false;