On Tue, Oct 29, 2019 at 02:19:25PM -0600, Jeff Law wrote:
> On 10/29/19 2:03 PM, Mikael Tillenius wrote:
> > I am using a cross compiler for Renesas H8S. In a few places it
> > generates really bad code. Given the following program:
> >
> > struct s {
> > char a, b;
> > char c[11];
> > } x[2];
> >
> > void test(int n)
> > {
> > struct s *sp = &x[n];
> >
> > sp->a = 1;
> > sp->b = 1;
> > }
> As we leave gimple the code looks like:
>
> MEM <struct s[2]> [(struct s *)&x][n_1(D)].a = 1;
> MEM <struct s[2]> [(struct s *)&x][n_1(D)].b = 1;
>
> One might argue that DOM or FRE should have created a common
> subexpression for the address arithmetic here. Even so it's not bad.
>
> CSE doesn't do its job though. THere's clearly a REG_EQUAL note which
> should have allowed it to at least cleanup the redundant multiplication
> for the address calculation.
And on other targets it does do its job fine, say riscv32, or m68k -O1
(the -O1 to prevent the two stores from being optimised into one).
I haven't managed to find another target where multiplication by 13 is
done with a libcall though. Maybe I should look harder.
> I recommend filing a bug report.
+1
Segher
