Hi!
On Mon, Sep 12, 2022 at 12:40:31AM +0100, Roger Sayle wrote:
> * gcc/combine.cc (expand_compound_operation): Don't expand/transform
> ZERO_EXTEND or SIGN_EXTEND on targets where rtx_cost claims they are
> cheap. If gen_lowpart returns a SUBREG of something other than a
> REG or a MEM, i.e. invalid RTL, return the original expression.
This needs testing and analysis on all platforms.
> @@ -7309,7 +7319,11 @@ expand_compound_operation (rtx x)
> if (modewidth >= pos + len)
> {
> tem = gen_lowpart (mode, XEXP (x, 0));
> - if (!tem || GET_CODE (tem) == CLOBBER)
> + if (!tem
> + || GET_CODE (tem) == CLOBBER
> + || (GET_CODE (tem) == SUBREG
> + && !REG_P (SUBREG_REG (tem))
> + && !MEM_P (SUBREG_REG (tem))))
> return x;
Why handle subregs of memory here? Those are antiquated, and should go
away pretty soon.
All of {expand,make}_compound_operation should be removed. But this is
non-trivial work. All of {SIGN,ZERO}_EXTRACT should be eradicated as
well, in my opinion.
Segher
