On Tue, 20 Feb 2024, Jakub Jelinek wrote:
> On Tue, Feb 20, 2024 at 09:01:10AM +0100, Richard Biener wrote:
> > I'm not sure those would be really equivalent (MEM_REF vs. V_C_E
> > as well as combined vs. split). It really depends how RTL expansion
> > handles this (as you can see padding can be fun here).
> >
> > So I'd be nervous for a match.pd rule here (also we can't match
> > memory defs).
>
> Ok. Perhaps forwprop then; anyway, that would be an optimization.
>
> > As for your patch I'd go with a MEM_REF unconditionally, I don't
> > think we want different behavior whether there's padding or not ...
>
> I've made it conditional so that the MEM_REFs don't appear that often in the
> FE trees, but maybe that is fine.
>
> The unconditional patch would then be:
>
> 2024-02-20 Jakub Jelinek <[email protected]>
>
> gcc/c-family/
> * c-common.cc (resolve_overloaded_atomic_exchange): Instead of setting
> p1 to VIEW_CONVERT_EXPR<I_type> (*p1), set it to MEM_REF with p1 and
> (typeof (p1)) 0 operands and I_type type.
> (resolve_overloaded_atomic_compare_exchange): Similarly for p2.
> gcc/cp/
> * pt.cc (tsubst_expr): Handle MEM_REF.
> gcc/testsuite/
> * g++.dg/ext/atomic-5.C: New test.
>
> --- gcc/c-family/c-common.cc.jj 2024-02-17 16:40:42.831571693 +0100
> +++ gcc/c-family/c-common.cc 2024-02-20 10:58:56.599865656 +0100
> @@ -7793,9 +7793,14 @@ resolve_overloaded_atomic_exchange (loca
> /* Convert object pointer to required type. */
> p0 = build1 (VIEW_CONVERT_EXPR, I_type_ptr, p0);
> (*params)[0] = p0;
> - /* Convert new value to required type, and dereference it. */
> - p1 = build_indirect_ref (loc, p1, RO_UNARY_STAR);
> - p1 = build1 (VIEW_CONVERT_EXPR, I_type, p1);
> + /* Convert new value to required type, and dereference it.
> + If *p1 type can have padding or may involve floating point which
> + could e.g. be promoted to wider precision and demoted afterwards,
> + state of padding bits might not be preserved. */
> + build_indirect_ref (loc, p1, RO_UNARY_STAR);
> + p1 = build2_loc (loc, MEM_REF, I_type,
> + build1 (VIEW_CONVERT_EXPR, I_type_ptr, p1),
Why the V_C_E to I_type_ptr? The type of p1 doesn't
really matter (unless it could be a non-pointer).
Also note that I_type needs to be properly address-space qualified
in case the access should be to an address-space. Formerly with
the INDIRECT_REF that would likely be automagic.
> + build_zero_cst (TREE_TYPE (p1)));
> (*params)[1] = p1;
>
> /* Move memory model to the 3rd position, and end param list. */
> @@ -7873,9 +7878,14 @@ resolve_overloaded_atomic_compare_exchan
> p1 = build1 (VIEW_CONVERT_EXPR, I_type_ptr, p1);
> (*params)[1] = p1;
>
> - /* Convert desired value to required type, and dereference it. */
> - p2 = build_indirect_ref (loc, p2, RO_UNARY_STAR);
> - p2 = build1 (VIEW_CONVERT_EXPR, I_type, p2);
> + /* Convert desired value to required type, and dereference it.
> + If *p2 type can have padding or may involve floating point which
> + could e.g. be promoted to wider precision and demoted afterwards,
> + state of padding bits might not be preserved. */
> + build_indirect_ref (loc, p2, RO_UNARY_STAR);
> + p2 = build2_loc (loc, MEM_REF, I_type,
> + build1 (VIEW_CONVERT_EXPR, I_type_ptr, p2),
> + build_zero_cst (TREE_TYPE (p2)));
> (*params)[2] = p2;
>
> /* The rest of the parameters are fine. NULL means no special return value
> --- gcc/cp/pt.cc.jj 2024-02-17 16:40:42.868571182 +0100
> +++ gcc/cp/pt.cc 2024-02-20 10:57:36.646973603 +0100
> @@ -20088,6 +20088,14 @@ tsubst_expr (tree t, tree args, tsubst_f
> RETURN (r);
> }
>
> + case MEM_REF:
> + {
> + tree op0 = RECUR (TREE_OPERAND (t, 0));
> + tree op1 = RECUR (TREE_OPERAND (t, 0));
> + tree new_type = tsubst (TREE_TYPE (t), args, complain, in_decl);
> + RETURN (build2_loc (EXPR_LOCATION (t), MEM_REF, new_type, op0, op1));
> + }
> +
> case NOP_EXPR:
> {
> tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
> --- gcc/testsuite/g++.dg/ext/atomic-5.C.jj 2024-02-20 10:57:36.647973589
> +0100
> +++ gcc/testsuite/g++.dg/ext/atomic-5.C 2024-02-20 10:57:36.647973589
> +0100
> @@ -0,0 +1,42 @@
> +// { dg-do compile { target c++14 } }
> +
> +template <int N>
> +void
> +foo (long double *ptr, long double *val, long double *ret)
> +{
> + __atomic_exchange (ptr, val, ret, __ATOMIC_RELAXED);
> +}
> +
> +template <int N>
> +bool
> +bar (long double *ptr, long double *exp, long double *des)
> +{
> + return __atomic_compare_exchange (ptr, exp, des, false,
> + __ATOMIC_RELAXED, __ATOMIC_RELAXED);
> +}
> +
> +bool
> +baz (long double *p, long double *q, long double *r)
> +{
> + foo<0> (p, q, r);
> + foo<1> (p + 1, q + 1, r + 1);
> + return bar<0> (p + 2, q + 2, r + 2) || bar<1> (p + 3, q + 3, r + 3);
> +}
> +
> +constexpr int
> +qux (long double *ptr, long double *val, long double *ret)
> +{
> + __atomic_exchange (ptr, val, ret, __ATOMIC_RELAXED);
> + return 0;
> +}
> +
> +constexpr bool
> +corge (long double *ptr, long double *exp, long double *des)
> +{
> + return __atomic_compare_exchange (ptr, exp, des, false,
> + __ATOMIC_RELAXED, __ATOMIC_RELAXED);
> +}
> +
> +long double a[6];
> +const int b = qux (a, a + 1, a + 2);
> +const bool c = corge (a + 3, a + 4, a + 5);
>
>
> Jakub
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
