Re: [PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Jeff Law <law at redhat dot com>]

On 03/31/2017 03:40 PM, Segher Boessenkool wrote:
> The function simplify_binary_operation_1 has code that does
> /* Convert (compare (gt (flags) 0) (lt (flags) 0)) to (flags).  */
> but this transformation is only valid if "flags" has the same machine
> mode as the outer compare.  This fixes it.
>
> Bootstrapped and tested on powerpc64-linux {-m32,-m64} (and tested the
> new testcase with {-m32,-m64}{,-misel}).  Is this okay for trunk?
>
>
> Segher
>
>
> 2017-03-31  Segher Boessenkool  <segher@kernel.crashing.org>
>
> 	PR rtl-optimization/60818
> 	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
> 	a compare of comparisons with the thing compared if this results
> 	in a different machine mode.
>
> gcc/testsuite/
> 	PR rtl-optimization/60818
> 	* gcc.c-torture/compile/pr60818.c: New testcase.
Doesn't seem like a regression.  But I can't see how it could possibly 
result in any correctness issues -- the absolute worst would be a 
performance issue and even that seems highly unlikely.

OK for the trunk if you think it's worth fixing for gcc-7.  Else it's 
pre-approved for gcc-8.


jeff