> Second patch cleans up predictors that do not use a value from predict.def,
> but their value is derived from e.g. number of iterations of a loop.
> These predictors have set probability to PROB_UNINITIALIZED and
> analyze_branch.py
> does not compare statistics to values defined in predict.def.
>
> The patch is no-op.
OK, thanks!
Honza
>
> Martin
> >From 6f6f2d88d3141b1e1604698abf857fffbb42330e Mon Sep 17 00:00:00 2001
> From: marxin <mli...@suse.cz>
> Date: Wed, 27 Dec 2017 14:49:20 +0100
> Subject: [PATCH 2/5] Introduce PROB_UNINITIALIZED constant and use it in
> predict.def.
>
> gcc/ChangeLog:
>
> 2017-12-28 Martin Liska <mli...@suse.cz>
>
> * predict.c (predict_insn_def): Add new assert.
> (struct branch_predictor): Change type to signed integer.
> (test_prediction_value_range): Amend test to cover
> PROB_UNINITIALIZED.
> * predict.def (PRED_LOOP_ITERATIONS): Use the new constant.
> (PRED_LOOP_ITERATIONS_GUESSED): Likewise.
> (PRED_LOOP_ITERATIONS_MAX): Likewise.
> (PRED_LOOP_IV_COMPARE): Likewise.
> * predict.h (PROB_UNINITIALIZED): Define new constant.
> ---
> gcc/predict.c | 6 +++++-
> gcc/predict.def | 8 ++++----
> gcc/predict.h | 1 +
> 3 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/predict.c b/gcc/predict.c
> index 3ac18a2c5f2..51fd14205c2 100644
> --- a/gcc/predict.c
> +++ b/gcc/predict.c
> @@ -545,6 +545,7 @@ predict_insn_def (rtx_insn *insn, enum br_predictor
> predictor,
> enum prediction taken)
> {
> int probability = predictor_info[(int) predictor].hitrate;
> + gcc_assert (probability != PROB_UNINITIALIZED);
>
> if (taken != TAKEN)
> probability = REG_BR_PROB_BASE - probability;
> @@ -4185,7 +4186,7 @@ namespace selftest {
> struct branch_predictor
> {
> const char *name;
> - unsigned probability;
> + int probability;
> };
>
> #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) { NAME, HITRATE },
> @@ -4200,6 +4201,9 @@ test_prediction_value_range ()
>
> for (unsigned i = 0; predictors[i].name != NULL; i++)
> {
> + if (predictors[i].probability == PROB_UNINITIALIZED)
> + continue;
> +
> unsigned p = 100 * predictors[i].probability / REG_BR_PROB_BASE;
> ASSERT_TRUE (p > 50 && p <= 100);
> }
> diff --git a/gcc/predict.def b/gcc/predict.def
> index 0f37e399312..390b9a35fa7 100644
> --- a/gcc/predict.def
> +++ b/gcc/predict.def
> @@ -54,7 +54,7 @@ DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump",
> PROB_ALWAYS,
> /* Use number of loop iterations determined by # of iterations
> analysis to set probability. We don't want to use Dempster-Shaffer
> theory here, as the predictions is exact. */
> -DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
> +DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED,
> PRED_FLAG_FIRST_MATCH)
>
> /* Assume that any given atomic operation has low contention,
> @@ -71,11 +71,11 @@ DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect",
> PROB_VERY_LIKELY,
>
> /* Use number of loop iterations guessed by the contents of the loop. */
> DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
> - PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
> + PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH)
>
> /* Use number of loop iterations guessed by the contents of the loop. */
> DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations",
> - PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
> + PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH)
>
> /* Branch containing goto is probably not taken. */
> DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0)
> @@ -151,7 +151,7 @@ DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv
> compare",
>
> /* Use number of loop iterations determined by # of iterations analysis
> to set probability of branches that compares IV to loop bound variable.
> */
> -DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
> +DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED,
> PRED_FLAG_FIRST_MATCH)
>
> /* In the following code
> diff --git a/gcc/predict.h b/gcc/predict.h
> index 57715159b95..e4d1da090ca 100644
> --- a/gcc/predict.h
> +++ b/gcc/predict.h
> @@ -31,6 +31,7 @@ along with GCC; see the file COPYING3. If not see
> #define PROB_ALWAYS (REG_BR_PROB_BASE)
> #define PROB_UNLIKELY (REG_BR_PROB_BASE / 5 - 1)
> #define PROB_LIKELY (REG_BR_PROB_BASE - PROB_UNLIKELY)
> +#define PROB_UNINITIALIZED (-1)
>
> #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) ENUM,
> enum br_predictor
> --
> 2.14.3
>
