Re: [PATCH v2] combine: Narrow comparison of memory and constant

[Jeff Law <jeffreyalaw@gmail.com>]

On 6/19/23 08:23, Stefan Schulze Frielinghaus via Gcc-patches wrote:
> Comparisons between memory and constants might be done in a smaller mode
> resulting in smaller constants which might finally end up as immediates
> instead of in the literal pool.
> 
> For example, on s390x a non-symmetric comparison like
>    x <= 0x3fffffffffffffff
> results in the constant being spilled to the literal pool and an 8 byte
> memory comparison is emitted.  Ideally, an equivalent comparison
>    x0 <= 0x3f
> where x0 is the most significant byte of x, is emitted where the
> constant is smaller and more likely to materialize as an immediate.
> 
> Similarly, comparisons of the form
>    x >= 0x4000000000000000
> can be shortened into x0 >= 0x40.
> 
> Bootstrapped and regtested on s390x, x64, aarch64, and powerpc64le.
> Note, the new tests show that for the mentioned little-endian targets
> the optimization does not materialize since either the costs of the new
> instructions are higher or they do not match.  Still ok for mainline?
> 
> gcc/ChangeLog:
> 
> 	* combine.cc (simplify_compare_const): Narrow comparison of
> 	memory and constant.
> 	(try_combine): Adapt new function signature.
> 	(simplify_comparison): Adapt new function signature.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.dg/cmp-mem-const-1.c: New test.
> 	* gcc.dg/cmp-mem-const-2.c: New test.
> 	* gcc.dg/cmp-mem-const-3.c: New test.
> 	* gcc.dg/cmp-mem-const-4.c: New test.
> 	* gcc.dg/cmp-mem-const-5.c: New test.
> 	* gcc.dg/cmp-mem-const-6.c: New test.
> 	* gcc.target/s390/cmp-mem-const-1.c: New test.
Sorry.  I'd looked at this a while back, wanted to take another looksie 
and totally forgot about it.

OK for the trunk.  Thanks for your patience.

jeff