On Tue, 28 Feb 2012, Martin Jambor wrote:
> Hi,
>
> this patch fixes misaligned reads through MEM_REFs such as the one in
> the testcase which currently fails on both sparc64 and ia64 (again,
> the array and the loop are there to cross ia64 cache line and fail
> there too). The patch has to be applied last in the series so that
> the current LHS expansion does not attempt to use the new code.
>
> The mechanism is again very similar, except that we call
> extract_bit_field instead now. We do not need to care about the
> mem_ref_refers_to_non_mem_p case because that is already handled at
> this stage. On the other hand, messing with complex types actually
> breaks currently working testcases such as the one from the previous
> patch (I have not really fully investigated what goes on so far but it
> genuinely seems to work) so again I punt for complex modes.
>
> There are two more movmisalign_optab generations in this function.
> There is the TARGET_MEM_REF case which I intend to piggy-back on in
> the same way like MEM_REF is handled in this patch once it leaves the
> RFC stage. Finally, movmisalign_optab is also generated in
> VIEW_CONVERT_EXPR case but as far as I understand the code, misaligned
> loads are already handled there (only perhaps we should use
> SLOW_UNALIGNED_ACCESS instead of STRICT_ALIGNMENT there?).
>
> Thanks,
>
> Martin
>
>
> 2012-02-28 Martin Jambor <mjam...@suse.cz>
>
> * expr.c (expand_expr_real_1): handle misaligned scalar reads from
> memory through MEM_REFs by calling extract_bit_field.
>
> * testsuite/gcc.dg/misaligned-expand-1.c: New test.
>
>
> Index: src/gcc/expr.c
> ===================================================================
> --- src.orig/gcc/expr.c
> +++ src/gcc/expr.c
> @@ -9453,21 +9453,29 @@ expand_expr_real_1 (tree exp, rtx target
> if (TREE_THIS_VOLATILE (exp))
> MEM_VOLATILE_P (temp) = 1;
> if (mode != BLKmode
> - && align < GET_MODE_ALIGNMENT (mode)
> - /* If the target does not have special handling for unaligned
> - loads of mode then it can use regular moves for them. */
> - && ((icode = optab_handler (movmisalign_optab, mode))
> - != CODE_FOR_nothing))
> + && !COMPLEX_MODE_P (mode)
I think the COMPLEX_MODE_P checks are wrong, you need to debug what
exactly goes wrong if we enter with such mode here.
Otherwise this patch looks ok as well.
Thanks,
Richard.
> + && align < GET_MODE_ALIGNMENT (mode))
> {
> - struct expand_operand ops[2];
> + if ((icode = optab_handler (movmisalign_optab, mode))
> + != CODE_FOR_nothing)
> + {
> + struct expand_operand ops[2];
>
> - /* We've already validated the memory, and we're creating a
> - new pseudo destination. The predicates really can't fail,
> - nor can the generator. */
> - create_output_operand (&ops[0], NULL_RTX, mode);
> - create_fixed_operand (&ops[1], temp);
> - expand_insn (icode, 2, ops);
> - return ops[0].value;
> + /* We've already validated the memory, and we're creating a
> + new pseudo destination. The predicates really can't fail,
> + nor can the generator. */
> + create_output_operand (&ops[0], NULL_RTX, mode);
> + create_fixed_operand (&ops[1], temp);
> + expand_insn (icode, 2, ops);
> + return ops[0].value;
> + }
> + else if (!COMPLEX_MODE_P (mode)
> + && SLOW_UNALIGNED_ACCESS (mode, align))
> + temp = extract_bit_field (temp, GET_MODE_BITSIZE (mode),
> + 0, TYPE_UNSIGNED (TREE_TYPE (exp)),
> true,
> + (modifier == EXPAND_STACK_PARM
> + ? NULL_RTX : target),
> + mode, mode);
> }
> return temp;
> }
> Index: src/gcc/testsuite/gcc.dg/misaligned-expand-1.c
> ===================================================================
> --- /dev/null
> +++ src/gcc/testsuite/gcc.dg/misaligned-expand-1.c
> @@ -0,0 +1,41 @@
> +/* Test that expand can generate correct loads of misaligned data even on
> + strict alignment platforms. */
> +
> +/* { dg-do run } */
> +/* { dg-options "-O0" } */
> +
> +extern void abort ();
> +
> +typedef unsigned int myint __attribute__((aligned(1)));
> +
> +unsigned int
> +foo (myint *p)
> +{
> + return *p;
> +}
> +
> +#define cst 0xdeadbeef
> +#define NUM 8
> +
> +struct blah
> +{
> + char c;
> + myint i[NUM];
> +};
> +
> +struct blah g;
> +
> +int
> +main (int argc, char **argv)
> +{
> + int i, k;
> + for (k = 0; k < NUM; k++)
> + {
> + g.i[k] = cst;
> + i = foo (&g.i[k]);
> +
> + if (i != cst)
> + abort ();
> + }
> + return 0;
> +}
>
>
--
Richard Guenther <rguent...@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer
