#include "toplev.h"
#include "params.h"
#include "langhooks.h"
+#include "tree-inline.h"
/* This pass inserts prefetch instructions to optimize cache usage during
accesses to arrays in loops. It processes loops sequentially and:
/* Magic constants follow. These should be replaced by machine specific
numbers. */
-/* A number that should roughly correspond to the number of instructions
- executed before the prefetch is completed. */
-
-#ifndef PREFETCH_LATENCY
-#define PREFETCH_LATENCY 200
-#endif
-
-/* Number of prefetches that can run at the same time. */
-
-#ifndef SIMULTANEOUS_PREFETCHES
-#define SIMULTANEOUS_PREFETCHES 3
-#endif
-
/* True if write can be prefetched by a read prefetch. */
#ifndef WRITE_CAN_USE_READ_PREFETCH
#define READ_CAN_USE_WRITE_PREFETCH 0
#endif
-/* Cache line size. Assumed to be a power of two. */
+/* The size of the block loaded by a single prefetch. Usually, this is
+ the same as cache line size (at the moment, we only consider one level
+ of cache hierarchy). */
#ifndef PREFETCH_BLOCK
-#define PREFETCH_BLOCK 32
+#define PREFETCH_BLOCK L1_CACHE_LINE_SIZE
#endif
/* Do we have a forward hardware sequential prefetching? */
fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step);
fprintf (file, ")\n");
- fprintf (dump_file, " delta ");
+ fprintf (file, " delta ");
fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta);
fprintf (file, "\n");
ibase = iv.base;
step = iv.step;
- if (zero_p (step))
- istep = 0;
- else
- {
- if (!cst_and_fits_in_hwi (step))
- return false;
- istep = int_cst_value (step);
- }
+ if (!cst_and_fits_in_hwi (step))
+ return false;
+ istep = int_cst_value (step);
if (TREE_CODE (ibase) == PLUS_EXPR
&& cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1)))
return true;
}
-/* Tries to express REF in shape &BASE + STEP * iter + DELTA, where DELTA and
+/* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and
STEP are integer constants and iter is number of iterations of LOOP. The
- reference occurs in statement STMT. */
+ reference occurs in statement STMT. Strips nonaddressable component
+ references from REF_P. */
static bool
-analyze_ref (struct loop *loop, tree ref, tree *base,
+analyze_ref (struct loop *loop, tree *ref_p, tree *base,
HOST_WIDE_INT *step, HOST_WIDE_INT *delta,
tree stmt)
{
struct ar_data ar_data;
tree off;
HOST_WIDE_INT bit_offset;
+ tree ref = *ref_p;
*step = 0;
*delta = 0;
&& DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))
ref = TREE_OPERAND (ref, 0);
+ *ref_p = ref;
+
for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0))
{
off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1));
HOST_WIDE_INT step, delta;
struct mem_ref_group *agrp;
- if (!analyze_ref (loop, ref, &base, &step, &delta, stmt))
+ if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt))
return;
/* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
{
stmt = bsi_stmt (bsi);
- if (TREE_CODE (stmt) != MODIFY_EXPR)
+ if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT)
continue;
- lhs = TREE_OPERAND (stmt, 0);
- rhs = TREE_OPERAND (stmt, 1);
+ lhs = GIMPLE_STMT_OPERAND (stmt, 0);
+ rhs = GIMPLE_STMT_OPERAND (stmt, 1);
if (REFERENCE_CLASS_P (rhs))
gather_memory_references_ref (loop, &refs, rhs, false, stmt);
schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor,
unsigned ahead)
{
- unsigned max_prefetches, n_prefetches;
+ unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots;
+ unsigned slots_per_prefetch;
struct mem_ref *ref;
bool any = false;
- max_prefetches = (SIMULTANEOUS_PREFETCHES * unroll_factor) / ahead;
- if (max_prefetches > (unsigned) SIMULTANEOUS_PREFETCHES)
- max_prefetches = SIMULTANEOUS_PREFETCHES;
+ /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */
+ remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES;
+ /* The prefetch will run for AHEAD iterations of the original loop, i.e.,
+ AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration,
+ it will need a prefetch slot. */
+ slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor;
if (dump_file && (dump_flags & TDF_DETAILS))
- fprintf (dump_file, "Max prefetches to issue: %d.\n", max_prefetches);
-
- if (!max_prefetches)
- return false;
+ fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n",
+ slots_per_prefetch);
/* For now we just take memory references one by one and issue
prefetches for as many as possible. The groups are sorted
if (!should_issue_prefetch_p (ref))
continue;
- ref->issue_prefetch_p = true;
-
- /* If prefetch_mod is less then unroll_factor, we need to insert
- several prefetches for the reference. */
+ /* If we need to prefetch the reference each PREFETCH_MOD iterations,
+ and we unroll the loop UNROLL_FACTOR times, we need to insert
+ ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each
+ iteration. */
n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
/ ref->prefetch_mod);
- if (max_prefetches <= n_prefetches)
- return true;
+ prefetch_slots = n_prefetches * slots_per_prefetch;
+
+ /* If more than half of the prefetches would be lost anyway, do not
+ issue the prefetch. */
+ if (2 * remaining_prefetch_slots < prefetch_slots)
+ continue;
+
+ ref->issue_prefetch_p = true;
- max_prefetches -= n_prefetches;
+ if (remaining_prefetch_slots <= prefetch_slots)
+ return true;
+ remaining_prefetch_slots -= prefetch_slots;
any = true;
}
issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead)
{
HOST_WIDE_INT delta;
- tree addr, addr_base, prefetch, params, write_p;
+ tree addr, addr_base, prefetch, write_p;
block_stmt_iterator bsi;
unsigned n_prefetches, ap;
/ ref->prefetch_mod);
addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node);
addr_base = force_gimple_operand_bsi (&bsi, unshare_expr (addr_base), true, NULL);
+ write_p = ref->write_p ? integer_one_node : integer_zero_node;
for (ap = 0; ap < n_prefetches; ap++)
{
addr = force_gimple_operand_bsi (&bsi, unshare_expr (addr), true, NULL);
/* Create the prefetch instruction. */
- write_p = ref->write_p ? integer_one_node : integer_zero_node;
- params = tree_cons (NULL_TREE, addr,
- tree_cons (NULL_TREE, write_p, NULL_TREE));
-
- prefetch = build_function_call_expr (built_in_decls[BUILT_IN_PREFETCH],
- params);
+ prefetch = build_call_expr (built_in_decls[BUILT_IN_PREFETCH],
+ 2, addr, write_p);
bsi_insert_before (&bsi, prefetch, BSI_SAME_STMT);
}
}
/* Determine the coefficient by that unroll LOOP, from the information
contained in the list of memory references REFS. Description of
- umber of iterations of LOOP is stored to DESC. AHEAD is the number
- of iterations ahead that we need to prefetch. NINSNS is number of
- insns of the LOOP. */
+ umber of iterations of LOOP is stored to DESC. NINSNS is the number of
+ insns of the LOOP. EST_NITER is the estimated number of iterations of
+ the loop, or -1 if no estimate is available. */
static unsigned
determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs,
- unsigned ahead, unsigned ninsns,
- struct tree_niter_desc *desc)
+ unsigned ninsns, struct tree_niter_desc *desc,
+ HOST_WIDE_INT est_niter)
{
- unsigned upper_bound, size_factor, constraint_factor;
- unsigned factor, max_mod_constraint, ahead_factor;
+ unsigned upper_bound;
+ unsigned nfactor, factor, mod_constraint;
struct mem_ref_group *agp;
struct mem_ref *ref;
- upper_bound = PARAM_VALUE (PARAM_MAX_UNROLL_TIMES);
-
- /* First check whether the loop is not too large to unroll. */
- size_factor = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns;
- if (size_factor <= 1)
+ /* First check whether the loop is not too large to unroll. We ignore
+ PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us
+ from unrolling them enough to make exactly one cache line covered by each
+ iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent
+ us from unrolling the loops too many times in cases where we only expect
+ gains from better scheduling and decreasing loop overhead, which is not
+ the case here. */
+ upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns;
+
+ /* If we unrolled the loop more times than it iterates, the unrolled version
+ of the loop would be never entered. */
+ if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound)
+ upper_bound = est_niter;
+
+ if (upper_bound <= 1)
return 1;
- if (size_factor < upper_bound)
- upper_bound = size_factor;
-
- max_mod_constraint = 1;
+ /* Choose the factor so that we may prefetch each cache just once,
+ but bound the unrolling by UPPER_BOUND. */
+ factor = 1;
for (agp = refs; agp; agp = agp->next)
for (ref = agp->refs; ref; ref = ref->next)
- if (should_issue_prefetch_p (ref)
- && ref->prefetch_mod > max_mod_constraint)
- max_mod_constraint = ref->prefetch_mod;
-
- /* Set constraint_factor as large as needed to be able to satisfy the
- largest modulo constraint. */
- constraint_factor = max_mod_constraint;
-
- /* If ahead is too large in comparison with the number of available
- prefetches, unroll the loop as much as needed to be able to prefetch
- at least partially some of the references in the loop. */
- ahead_factor = ((ahead + SIMULTANEOUS_PREFETCHES - 1)
- / SIMULTANEOUS_PREFETCHES);
-
- /* Unroll as much as useful, but bound the code size growth. */
- if (constraint_factor < ahead_factor)
- factor = ahead_factor;
- else
- factor = constraint_factor;
- if (factor > upper_bound)
- factor = upper_bound;
+ if (should_issue_prefetch_p (ref))
+ {
+ mod_constraint = ref->prefetch_mod;
+ nfactor = least_common_multiple (mod_constraint, factor);
+ if (nfactor <= upper_bound)
+ factor = nfactor;
+ }
if (!should_unroll_loop_p (loop, desc, factor))
return 1;
}
/* Issue prefetch instructions for array references in LOOP. Returns
- true if the LOOP was unrolled. LOOPS is the array containing all
- loops. */
+ true if the LOOP was unrolled. */
static bool
-loop_prefetch_arrays (struct loops *loops, struct loop *loop)
+loop_prefetch_arrays (struct loop *loop)
{
struct mem_ref_group *refs;
- unsigned ahead, ninsns, unroll_factor;
+ unsigned ahead, ninsns, time, unroll_factor;
+ HOST_WIDE_INT est_niter;
struct tree_niter_desc desc;
bool unrolled = false;
/* Step 3: determine the ahead and unroll factor. */
- /* FIXME: We should use not size of the loop, but the average number of
- instructions executed per iteration of the loop. */
- ninsns = tree_num_loop_insns (loop);
- ahead = (PREFETCH_LATENCY + ninsns - 1) / ninsns;
- unroll_factor = determine_unroll_factor (loop, refs, ahead, ninsns,
- &desc);
+ /* FIXME: the time should be weighted by the probabilities of the blocks in
+ the loop body. */
+ time = tree_num_loop_insns (loop, &eni_time_weights);
+ ahead = (PREFETCH_LATENCY + time - 1) / time;
+ est_niter = estimated_loop_iterations_int (loop, false);
+
+ /* The prefetches will run for AHEAD iterations of the original loop. Unless
+ the loop rolls at least AHEAD times, prefetching the references does not
+ make sense. */
+ if (est_niter >= 0 && est_niter <= (HOST_WIDE_INT) ahead)
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file,
+ "Not prefetching -- loop estimated to roll only %d times\n",
+ (int) est_niter);
+ goto fail;
+ }
+
+ ninsns = tree_num_loop_insns (loop, &eni_size_weights);
+ unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc,
+ est_niter);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Ahead %d, unroll factor %d\n", ahead, unroll_factor);
- /* If the loop rolls less than the required unroll factor, prefetching
- is useless. */
- if (unroll_factor > 1
- && cst_and_fits_in_hwi (desc.niter)
- && (unsigned HOST_WIDE_INT) int_cst_value (desc.niter) < unroll_factor)
- goto fail;
-
/* Step 4: what to prefetch? */
if (!schedule_prefetches (refs, unroll_factor, ahead))
goto fail;
iterations so that we do not issue superfluous prefetches. */
if (unroll_factor != 1)
{
- tree_unroll_loop (loops, loop, unroll_factor,
+ tree_unroll_loop (loop, unroll_factor,
single_dom_exit (loop), &desc);
unrolled = true;
}
return unrolled;
}
-/* Issue prefetch instructions for array references in LOOPS. */
+/* Issue prefetch instructions for array references in loops. */
-void
-tree_ssa_prefetch_arrays (struct loops *loops)
+unsigned int
+tree_ssa_prefetch_arrays (void)
{
- unsigned i;
+ loop_iterator li;
struct loop *loop;
bool unrolled = false;
+ int todo_flags = 0;
if (!HAVE_prefetch
/* It is possible to ask compiler for say -mtune=i486 -march=pentium4.
of processor costs and i486 does not have prefetch, but
-march=pentium4 causes HAVE_prefetch to be true. Ugh. */
|| PREFETCH_BLOCK == 0)
- return;
+ return 0;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Prefetching parameters:\n");
+ fprintf (dump_file, " simultaneous prefetches: %d\n",
+ SIMULTANEOUS_PREFETCHES);
+ fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY);
+ fprintf (dump_file, " L1 cache size: %d (%d bytes)\n",
+ L1_CACHE_SIZE, L1_CACHE_SIZE * L1_CACHE_LINE_SIZE);
+ fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE);
+ fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK);
+ fprintf (dump_file, "\n");
+ }
initialize_original_copy_tables ();
tree_cons (NULL_TREE,
const_ptr_type_node,
NULL_TREE));
- tree decl = lang_hooks.builtin_function ("__builtin_prefetch", type,
- BUILT_IN_PREFETCH, BUILT_IN_NORMAL,
- NULL, NULL_TREE);
+ tree decl = add_builtin_function ("__builtin_prefetch", type,
+ BUILT_IN_PREFETCH, BUILT_IN_NORMAL,
+ NULL, NULL_TREE);
DECL_IS_NOVOPS (decl) = true;
built_in_decls[BUILT_IN_PREFETCH] = decl;
}
here. */
gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0);
- for (i = loops->num - 1; i > 0; i--)
+ FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
{
- loop = loops->parray[i];
-
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "Processing loop %d:\n", loop->num);
- if (loop)
- unrolled |= loop_prefetch_arrays (loops, loop);
+ unrolled |= loop_prefetch_arrays (loop);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, "\n\n");
if (unrolled)
{
scev_reset ();
- cleanup_tree_cfg_loop ();
+ todo_flags |= TODO_cleanup_cfg;
}
free_original_copy_tables ();
+ return todo_flags;
}
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