Re: [RFC / CFT] PR c++/66192 - Remove TARGET_RELAXED_ORDERING and use load acquires.

[David Edelsohn <dje.gcc@gmail.com>]

On Fri, May 22, 2015 at 11:23 AM, Ramana Radhakrishnan
<ramana.radhakrishnan@foss.arm.com> wrote:

> So on powerpc where targetm.guard_mask_bit is false - this is what I see.
>
>
> {
>   static int * p;
>
>     static int * p;
>   if (<<cleanup_point (unsigned char) *(char *) &(long long int)
> __atomic_load_8 (&_ZGVZ1fvE1p, 2) == 0>>)
>     {
>       if (<<cleanup_point __cxa_guard_acquire (&_ZGVZ1fvE1p) != 0>>)
>         {
>           <<cleanup_point <<< Unknown tree: expr_stmt
>   TARGET_EXPR <D.2846, 0>;, p = (int *) operator new (4);;, D.2846 = 1;;,
> __cxa_guard_release (&_ZGVZ1fvE1p); >>>>>;
>         }
>     }
>   return <retval> = p;
> }
>
> with the following output - David - is this what you would expect ?
>
>
> 0:      addis 2,12,.TOC.-0b@ha
>         addi 2,2,.TOC.-0b@l
>         .localentry     _Z1fv,.-_Z1fv
>         mflr %r0
>         std %r30,-16(%r1)
>         std %r31,-8(%r1)
>         .cfi_register 65, 0
>         .cfi_offset 30, -16
>         .cfi_offset 31, -8
>         addis %r30,%r2,_ZGVZ1fvE1p@toc@ha
>         addi %r30,%r30,_ZGVZ1fvE1p@toc@l
>         std %r0,16(%r1)
>         stdu %r1,-64(%r1)
>         .cfi_def_cfa_offset 64
>         .cfi_offset 65, 16
>         addis %r10,%r2,_ZGVZ1fvE1p@toc@ha               # gpr load fusion,
> type long
>         ld %r10,_ZGVZ1fvE1p@toc@l(%r10)
>         cmpw %cr7,%r10,%r10
>         bne- %cr7,$+4
>         isync
>         rlwinm %r9,%r10,0,0xff
>         std %r10,32(%r1)
>         cmpwi %cr7,%r9,0
>         beq %cr7,.L11
> .L9:
>         addi %r1,%r1,64
>         .cfi_remember_state
>         .cfi_def_cfa_offset 0
>         addis %r3,%r2,_ZZ1fvE1p@toc@ha          # gpr load fusion, type long
>         ld %r3,_ZZ1fvE1p@toc@l(%r3)
>         ld %r0,16(%r1)
>         ld %r30,-16(%r1)
>         ld %r31,-8(%r1)
>         mtlr %r0
>         .cfi_restore 65
>         .cfi_restore 31
>         .cfi_restore 30
>         blr
>         .p2align 4,,15
> .L11:
>         .cfi_restore_state
>         mr %r3,%r30

It looks reasonable, but we really need to examine the code produced
by the final version of the patch for some examples.

Thanks, David