Re: ppc64 minimal-toc problem.

[Alan Modra <amodra at bigpond dot net dot au>]

On Tue, Jul 17, 2001 at 02:48:03AM -0700, Geoff Keating wrote:
> > From: Alan Modra <amodra@bigpond.net.au>
> > On Tue, Jul 17, 2001 at 12:21:25AM -0700, Geoff Keating wrote:
> > > 
> > > which is pretty much what I'd expect, although I suspect 'mfcr' is not
> > > an instruction GCC should really be using...
> > 
> > I was using 3.0 branch sources, unchanged.  configured with
> > --host=i686-linux --target=powerpc-ibm-aix5.1 --enable-languages=c,
> > gcc/Makefile modified to set {,MAYBE_}USE_COLLECT2 null to get around a
> > build problem, then "-O2 -maix64 -mminimal-toc" gives me
> > 
> > .foo:
> >         ld 30,LCTOC..1(2)
> >         ld 0,0(3)
> >         ld 9,LC..0(30)
> >         and. 9,0,9
> >         mfcr 3
> >         rlwinm 3,3,3,1
> >         blr
> 
> That's interesting.  Have you tried debugging the problem?  As I said,
> it seems to work on the mainline.

Mainline works for me too.  On the branch, I'm seeing .19.lreg

(insn 47 11 52 (parallel[ 
            (set (reg:CC 91)
                (compare:CC (and:DI (reg:DI 83)
                        (const_double (const_int 0 [0x0]) -2147483648 [0x80000000] 0 [0x0]))
                    (const_int 0 [0x0])))
            (clobber (scratch:DI))
            (clobber (scratch:CC))
        ] ) 268 {*anddi3_internal2} (insn_list 11 (nil))
    (expr_list:REG_DEAD (reg:DI 83)
        (expr_list:REG_UNUSED (scratch:DI)
            (expr_list:REG_UNUSED (scratch:CC)
                (nil)))))

turning into .20.greg

(insn 56 11 57 (use (const_double (mem/u/f:DI (symbol_ref/u:DI ("*LC..0")) 5) -2147483648 [0x80000000] 0 [0x0])) -1 (nil)
    (nil))

(insn 57 56 47 (set (reg:DI 9 r9)
        (mem/u:DI (plus:DI (reg:DI 30 r30)
                (const:DI (minus:DI (symbol_ref/u:DI ("*LC..0"))
                        (symbol_ref:DI ("*LCTOC..1"))))) 6)) 294 {*movdi_internal64} (nil)
    (nil))

(insn 47 57 52 (parallel[ 
            (set (reg:CC 68 cr0 [91])
                (compare:CC (and:DI (reg:DI 0 r0 [83])
                        (reg:DI 9 r9))
                    (const_int 0 [0x0])))
            (clobber (reg:DI 9 r9))
            (clobber (scratch:CC))
        ] ) 268 {*anddi3_internal2} (insn_list 11 (nil))
    (nil))

This being the only use of the toc and r30 in this function, we run into
a problem as reload doesn't set regs_ever_live for r30.

On the other hand, mainline puts the constant in the toc during initial
rtl generation, apparently due to differences between mainline and branch
rs6000.c:logical_operand;  The mainline version returns 0 for
const_double (0, 0x80000000) while the branch returns 1.  One solution
for my testcase then is to install the mainline version of logical_operand
to the branch, but I'm worried that there might be other cases where the
toc is used for the first time during reload.

Alan Modra

PS. I see I mailed my patch to gnu.gcc.org instead of gcc.gnu.org.  If
anyone wants a copy, please ask.