Can the test case be improved so that expected prediction results is
checked (with the help of more dumping such as blah blah is predicted
to be taken/not taken with probability xyz) ?
Also the more test cases need to be added to cover more cases >base, >
base +1, >=base +2, < base+1, <=base+1 etc -- even though expression
reassociation will normalize them ...
Thanks,
David
On Wed, Mar 28, 2012 at 4:54 PM, Dehao Chen <de...@google.com> wrote:
> Hi,
>
> This patch handles the comparison of iv against the loop iv initial
> value. Previously, we only handle the comparison of iv against its
> bound.
>
> Bootstrapped and passed all regression tests.
>
> Ok for google branches?
>
> Thanks,
> Dehao
>
> 2012-03-29 Dehao Chen <de...@google.com>
>
> * predict.c (predict_iv_comparison): Add the comparison of induction
> variable against its initial value.
>
> 2012-03-29 Dehao Chen <de...@google.com>
>
> * gcc.dg/predict-5.c: Check if LOOP_IV_COMPARE static predict
> heuristic is working properly.
>
> Index: gcc/testsuite/gcc.dg/predict-5.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/predict-5.c (revision 0)
> +++ gcc/testsuite/gcc.dg/predict-5.c (revision 0)
> @@ -0,0 +1,21 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
> +
> +extern int global;
> +
> +int bar(int);
> +
> +void foo (int base, int bound)
> +{
> + int i, ret = 0;
> + for (i = base; i <= bound; i++)
> + {
> + if (i > base + 2)
> + global += bar (i);
> + else
> + global += bar (i + 1);
> + }
> +}
> +
> +/* { dg-final { scan-tree-dump "loop iv compare heuristics"
> "profile_estimate"} } */
> +/* { dg-final { cleanup-tree-dump "profile_estimate" } } */
> Index: gcc/predict.c
> ===================================================================
> --- gcc/predict.c (revision 185903)
> +++ gcc/predict.c (working copy)
> @@ -1185,8 +1185,7 @@
> return;
> }
>
> - if (!expr_coherent_p (loop_bound_var, compare_var)
> - || loop_iv_base_var != compare_base)
> + if (loop_iv_base_var != compare_base)
> return;
>
> /* If loop bound, base and compare bound are all constents, we can
> @@ -1230,34 +1229,52 @@
> return;
> }
>
> - if ((loop_bound_code == LT_EXPR || loop_bound_code == LE_EXPR)
> - && (compare_code == LT_EXPR || compare_code == LE_EXPR))
> - predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> - else if ((loop_bound_code == GT_EXPR || loop_bound_code == GE_EXPR)
> - && (compare_code == GT_EXPR || compare_code == GE_EXPR))
> - predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> - else if (loop_bound_code == NE_EXPR)
> - {
> - /* If the loop backedge condition is "(i != bound)", we do
> - the comparison based on the step of IV:
> - * step < 0 : backedge condition is like (i > bound)
> - * step > 0 : backedge condition is like (i < bound) */
> - gcc_assert (loop_bound_step != 0);
> + if (expr_coherent_p (loop_bound_var, compare_var))
> + {
> + if ((loop_bound_code == LT_EXPR || loop_bound_code == LE_EXPR)
> + && (compare_code == LT_EXPR || compare_code == LE_EXPR))
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> + else if ((loop_bound_code == GT_EXPR || loop_bound_code == GE_EXPR)
> + && (compare_code == GT_EXPR || compare_code == GE_EXPR))
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> + else if (loop_bound_code == NE_EXPR)
> + {
> + /* If the loop backedge condition is "(i != bound)", we do
> + the comparison based on the step of IV:
> + * step < 0 : backedge condition is like (i > bound)
> + * step > 0 : backedge condition is like (i < bound) */
> + gcc_assert (loop_bound_step != 0);
> + if (loop_bound_step > 0
> + && (compare_code == LT_EXPR
> + || compare_code == LE_EXPR))
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> + else if (loop_bound_step < 0
> + && (compare_code == GT_EXPR
> + || compare_code == GE_EXPR))
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> + else
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, NOT_TAKEN);
> + }
> + else
> + /* The branch is predicted not-taken if loop_bound_code is
> + opposite with compare_code. */
> + predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, NOT_TAKEN);
> + }
> + else if (expr_coherent_p (loop_iv_base_var, compare_var))
> + {
> + /* For cases like:
> + for (i = s; i < h; i++)
> + if (i > s + 2) ....
> + The branch should be predicted taken. */
> if (loop_bound_step > 0
> - && (compare_code == LT_EXPR
> - || compare_code == LE_EXPR))
> + && (compare_code == GT_EXPR || compare_code == GE_EXPR))
> predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> else if (loop_bound_step < 0
> - && (compare_code == GT_EXPR
> - || compare_code == GE_EXPR))
> + && (compare_code == LT_EXPR || compare_code == LE_EXPR))
> predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, TAKEN);
> else
> predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, NOT_TAKEN);
> }
> - else
> - /* The branch is predicted not-taken if loop_bound_code is
> - opposite with compare_code. */
> - predict_edge_def (then_edge, PRED_LOOP_IV_COMPARE, NOT_TAKEN);
> }
>
> /* Predict edge probabilities by exploiting loop structure. */
