LGTM.
On Thu, Mar 15, 2018 at 3:25 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> Hi!
>
> The following testcase ICEs on arm (or other strict alignment targets).
> The problem is we have a call that returns a TREE_ADDRESSABLE type,
> and the lhs of the call is some memory that isn't known to be sufficiently
> aligned. expand_call in that case allocates a temporary, lets the call
> return into that object and copies it; this can't work for TREE_ADDRESSABLE
> types, assign_temp ICEs for those, we don't want to create temporaries in
> that case.
> This patch just avoids the temporary for TREE_ADDRESSABLE types and returns
> directly into the provided target memory.
> Either the compiler just doesn't know whether the target is properly aligned
> or not and it is properly aligned at runtime, then it will work properly,
> or it isn't properly aligned at runtime (perhaps compiler can even prove
> that) and it will be UB, which is user's fault.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2018-03-15 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/79085
> * calls.c (expand_call): For TREE_ADDRESSABLE rettype ignore alignment
> check and use address of target always.
>
> * g++.dg/opt/pr79085.C: New test.
>
> --- gcc/calls.c.jj 2018-02-22 12:37:02.641387687 +0100
> +++ gcc/calls.c 2018-03-15 15:17:42.596835316 +0100
> @@ -3422,9 +3422,14 @@ expand_call (tree exp, rtx target, int i
> if (CALL_EXPR_RETURN_SLOT_OPT (exp)
> && target
> && MEM_P (target)
> - && !(MEM_ALIGN (target) < TYPE_ALIGN (rettype)
> - && targetm.slow_unaligned_access (TYPE_MODE (rettype),
> - MEM_ALIGN (target))))
> + /* If rettype is addressable, we may not create a temporary.
> + If target is properly aligned at runtime and the compiler
> + just doesn't know about it, it will work fine, otherwise it
> + will be UB. */
> + && (TREE_ADDRESSABLE (rettype)
> + || !(MEM_ALIGN (target) < TYPE_ALIGN (rettype)
> + && targetm.slow_unaligned_access (TYPE_MODE (rettype),
> + MEM_ALIGN (target)))))
> structure_value_addr = XEXP (target, 0);
> else
> {
> --- gcc/testsuite/g++.dg/opt/pr79085.C.jj 2018-03-15 15:42:05.382927611
> +0100
> +++ gcc/testsuite/g++.dg/opt/pr79085.C 2018-03-15 15:32:56.626552182 +0100
> @@ -0,0 +1,24 @@
> +// PR c++/79085
> +// { dg-do compile }
> +// { dg-options "-Os" }
> +// { dg-additional-options "-mstrict-align" { target { aarch64*-*-*
> powerpc*-*-linux* powerpc*-*-elf* } } }
> +
> +void *operator new (__SIZE_TYPE__, void *p) { return p; }
> +
> +struct S
> +{
> + S ();
> + S (const S &);
> + ~S (void);
> + int i;
> +};
> +
> +S foo ();
> +
> +static char buf [sizeof (S) + 1];
> +
> +S *
> +bar ()
> +{
> + return new (buf + 1) S (foo ());
> +}
>
> Jakub
