On Wed, Jan 18, 2012 at 8:41 AM, Jiangning Liu <jiangning....@arm.com> wrote:
> This code change intends to improve scev for array element and reduce the
> common sub-expressions in loop, which may be introduced by multiple
> reference of expression like &a[i]. With this optimization the register
> pressure can be reduced in loops.
>
> The problem is originally from a real benchmark, and the test case only
> tries to detect the GIMPLE level changes.
>
> Bootstraped on x86-32. OK for trunk?
It's definitely not ok at this stage but at most for next stage1. But ...
> ChangeLog:
>
> 2012-01-05 Jiangning Liu <jiangning....@arm.com>
>
> * tree-scalar-evolution (interpret_rhs_expr): generate chrec for
> array reference.
>
> ChangeLog for testsuite:
>
> 2012-01-05 Jiangning Liu <jiangning....@arm.com>
>
> * gcc.dg/scev-1.c: New.
>
> diff --git a/gcc/testsuite/gcc.dg/scev-1.c b/gcc/testsuite/gcc.dg/scev-1.c
> new file mode 100644 index 0000000..28d5c93
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/scev-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +int *a_p;
> +int a[1000];
> +
> +f(int k)
> +{
> + int i;
> +
> + for (i=k; i<1000; i+=k) {
> + a_p = &a[i];
> + *a_p = 100;
> + }
> +}
> +
> +/* { dg-final { scan-tree-dump-times "&a" 1 "optimized" } } */
> +/* { dg-final { cleanup-tree-dump "optimized" } } */
> diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c index
> 2077c8d..de89fc4
> --- a/gcc/tree-scalar-evolution.c
> +++ b/gcc/tree-scalar-evolution.c
> @@ -1712,6 +1712,42 @@ interpret_rhs_expr (struct loop *loop, gimple
> at_stmt,
> switch (code)
> {
> case ADDR_EXPR:
> + if (TREE_CODE (TREE_OPERAND (rhs1, 0)) == ARRAY_REF)
This is a very narrow pattern-match. It doesn't allow for &a[i].x for example,
even if a[i] is a one-element structure. I think the canonical way of handling
ADDR_EXPR is to use sth like
base = get_inner_reference (TREE_OPERAND (rhs1, 0), ..., &offset, ...);
base = build1 (ADDR_EXPR, TREE_TYPE (rhs1), base);
chrec1 = analyze_scalar_evolution (loop, base);
chrec2 = analyze_scalar_evolution (loop, offset);
chrec1 = chrec_convert (type, chrec1, at_stmt);
chrec2 = chrec_convert (TREE_TYPE (offset), chrec2, at_stmt);
res = chrec_fold_plus (type, chrec1, chrec2);
where you probably need to handle scev_not_known when analyzing offset
(which might be NULL). You also need to add bitpos to the base address
(in bytes, of course). Note that the &MEM_REF case would naturally work
with this as well.
Richard.
> + {
> + tree array_ref;
> + tree var_decl, base, offset;
> + tree low_bound;
> + tree unit_size;
> + tree index;
> +
> + array_ref = TREE_OPERAND (rhs1, 0);
> + var_decl = TREE_OPERAND (array_ref, 0);
> + index = TREE_OPERAND (array_ref, 1);
> +
> + low_bound = array_ref_low_bound (array_ref);
> + unit_size = array_ref_element_size (array_ref);
> +
> + /* We assume all arrays have sizes that are a multiple of a byte.
> + First subtract the lower bound, if any, in the type of the
> + index, then convert to sizetype and multiply by the size of
> + the array element. */
> + if (! integer_zerop (low_bound))
> + index = fold_build2 (MINUS_EXPR, TREE_TYPE (index),
> + index, low_bound);
> +
> + offset = size_binop (MULT_EXPR,
> + fold_convert (sizetype, index),
> + unit_size);
> +
> + base = build1 (ADDR_EXPR, TREE_TYPE (rhs1), var_decl);
> + chrec1 = analyze_scalar_evolution (loop, base);
> + chrec2 = analyze_scalar_evolution (loop, offset);
> + chrec1 = chrec_convert (type, chrec1, at_stmt);
> + chrec2 = chrec_convert (TREE_TYPE (offset), chrec2, at_stmt);
> + res = chrec_fold_plus (type, chrec1, chrec2);
> + break;
> + }
> +
> /* Handle &MEM[ptr + CST] which is equivalent to POINTER_PLUS_EXPR.
> */
> if (TREE_CODE (TREE_OPERAND (rhs1, 0)) != MEM_REF)
> {
>
> Thanks,
> -Jiangning
