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Avoid accounting for non-existent vector loop versioning

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vect_analyze_loop_costing uses two profitability thresholds: a runtime
one and a static compile-time one.  The runtime one is simply the point
at which the vector loop is cheaper than the scalar loop, while the
static one also takes into account the cost of choosing between the
scalar and vector loops at runtime.  We compare this static cost against
the expected execution frequency to decide whether it's worth generating
any vector code at all.

However, we never reclaimed the cost of applying the runtime threshold
if it turned out that the vector code can always be used.  And we only
know whether that's true once we've calculated what the runtime
threshold would be.

2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vect_apply_runtime_profitability_check_p):
	New function.
	* tree-vect-loop-manip.c (vect_loop_versioning): Use it.
	* tree-vect-loop.c (vect_analyze_loop_2): Likewise.
	(vect_transform_loop): Likewise.
	(vect_analyze_loop_costing): Don't take the cost of versioning
	into account for the static profitability threshold if it turns
	out that no versioning is needed.

From-SVN: r278124
This commit is contained in:
Richard Sandiford 2019-11-13 09:05:59 +00:00 • committed by Richard Sandiford
parent d4b44b834e
commit 6eed64b96d
4 changed files with 48 additions and 11 deletions
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11
gcc/ChangeLog
View file

@ -1,3 +1,14 @@
2019-11-13 Richard Sandiford <richard.sandiford@arm.com>
* tree-vectorizer.h (vect_apply_runtime_profitability_check_p):
New function.
* tree-vect-loop-manip.c (vect_loop_versioning): Use it.
* tree-vect-loop.c (vect_analyze_loop_2): Likewise.
(vect_transform_loop): Likewise.
(vect_analyze_loop_costing): Don't take the cost of versioning
into account for the static profitability threshold if it turns
out that no versioning is needed.
2019-11-13 Jan Hubicka <hubicka@ucw.cz>
* ipa.c (cgraph_build_static_cdtor): Pass optimization_default_node

3
gcc/tree-vect-loop-manip.c
View file

@ -3171,8 +3171,7 @@ vect_loop_versioning (loop_vec_info loop_vinfo)
= LOOP_REQUIRES_VERSIONING_FOR_SIMD_IF_COND (loop_vinfo);
unsigned th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
if (th >= vect_vf_for_cost (loop_vinfo)
&& !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
if (vect_apply_runtime_profitability_check_p (loop_vinfo)
&& !ordered_p (th, versioning_threshold))
cond_expr = fold_build2 (GE_EXPR, boolean_type_node, scalar_loop_iters,
build_int_cst (TREE_TYPE (scalar_loop_iters),

34
gcc/tree-vect-loop.c
View file

@ -1690,6 +1690,24 @@ vect_analyze_loop_costing (loop_vec_info loop_vinfo)
return 0;
}
/* The static profitablity threshold min_profitable_estimate includes
the cost of having to check at runtime whether the scalar loop
should be used instead. If it turns out that we don't need or want
such a check, the threshold we should use for the static estimate
is simply the point at which the vector loop becomes more profitable
than the scalar loop. */
if (min_profitable_estimate > min_profitable_iters
&& !LOOP_REQUIRES_VERSIONING (loop_vinfo)
&& !LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo)
&& !LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo)
&& !vect_apply_runtime_profitability_check_p (loop_vinfo))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location, "no need for a runtime"
" choice between the scalar and vector loops\n");
min_profitable_estimate = min_profitable_iters;
}
HOST_WIDE_INT estimated_niter;
/* If we are vectorizing an epilogue then we know the maximum number of
@ -2226,8 +2244,7 @@ start_over:
/* Use the same condition as vect_transform_loop to decide when to use
the cost to determine a versioning threshold. */
if (th >= vect_vf_for_cost (loop_vinfo)
&& !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
if (vect_apply_runtime_profitability_check_p (loop_vinfo)
&& ordered_p (th, niters_th))
niters_th = ordered_max (poly_uint64 (th), niters_th);
@ -8250,14 +8267,13 @@ vect_transform_loop (loop_vec_info loop_vinfo)
run at least the (estimated) vectorization factor number of times
checking is pointless, too. */
th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
if (th >= vect_vf_for_cost (loop_vinfo)
&& !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo))
if (vect_apply_runtime_profitability_check_p (loop_vinfo))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location,
"Profitability threshold is %d loop iterations.\n",
th);
check_profitability = true;
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location,
"Profitability threshold is %d loop iterations.\n",
th);
check_profitability = true;
}
/* Make sure there exists a single-predecessor exit bb. Do this before

11
gcc/tree-vectorizer.h
View file

@ -1556,6 +1556,17 @@ vect_get_scalar_dr_size (dr_vec_info *dr_info)
return tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr_info->dr))));
}
/* Return true if LOOP_VINFO requires a runtime check for whether the
vector loop is profitable. */
inline bool
vect_apply_runtime_profitability_check_p (loop_vec_info loop_vinfo)
{
unsigned int th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
return (!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
&& th >= vect_vf_for_cost (loop_vinfo));
}
/* Source location + hotness information. */
extern dump_user_location_t vect_location;