X-Git-Url: http://git.sourceforge.jp/view?p=pf3gnuchains%2Fgcc-fork.git;a=blobdiff_plain;f=gcc%2Ftree-ssa-loop-prefetch.c;h=264d97bc1b57e248a0f6a4849380b1e275520762;hp=2424c4a1832ddaf12eccfb0cd3af80bda1c6faf9;hb=fa9f12bbe3098b9eb04e35ef6e346e0b85e5366e;hpb=5b5037b32317ffd475a733d701c4ad7f90592d7b diff --git a/gcc/tree-ssa-loop-prefetch.c b/gcc/tree-ssa-loop-prefetch.c index 2424c4a1832..264d97bc1b5 100644 --- a/gcc/tree-ssa-loop-prefetch.c +++ b/gcc/tree-ssa-loop-prefetch.c @@ -1,52 +1,52 @@ /* Array prefetching. - Copyright (C) 2005 Free Software Foundation, Inc. - + Copyright (C) 2005, 2007, 2008, 2009, 2010, 2011 + Free Software Foundation, Inc. + This file is part of GCC. - + GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the -Free Software Foundation; either version 2, or (at your option) any +Free Software Foundation; either version 3, or (at your option) any later version. - + GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. - + You should have received a copy of the GNU General Public License -along with GCC; see the file COPYING. If not, write to the Free -Software Foundation, 59 Temple Place - Suite 330, Boston, MA -02111-1307, USA. */ +along with GCC; see the file COPYING3. If not see +. */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" -#include "rtl.h" #include "tm_p.h" -#include "hard-reg-set.h" #include "basic-block.h" #include "output.h" -#include "diagnostic.h" +#include "tree-pretty-print.h" #include "tree-flow.h" #include "tree-dump.h" #include "timevar.h" #include "cfgloop.h" -#include "varray.h" -#include "expr.h" #include "tree-pass.h" -#include "ggc.h" #include "insn-config.h" #include "recog.h" #include "hashtab.h" #include "tree-chrec.h" #include "tree-scalar-evolution.h" -#include "toplev.h" +#include "diagnostic-core.h" #include "params.h" #include "langhooks.h" #include "tree-inline.h" #include "tree-data-ref.h" + + +/* FIXME: Needed for optabs, but this should all be moved to a TBD interface + between the GIMPLE and RTL worlds. */ +#include "expr.h" #include "optabs.h" /* This pass inserts prefetch instructions to optimize cache usage during @@ -80,7 +80,7 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA (2) has PREFETCH_MOD 64 (3) has PREFETCH_MOD 4 (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since - the cache line accessed by (4) is the same with probability only + the cache line accessed by (5) is the same with probability only 7/32. (5) has PREFETCH_MOD 1 as well. @@ -100,16 +100,43 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA while still within this bound (starting with those with lowest prefetch_mod, since they are responsible for most of the cache misses). - + 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD and PREFETCH_BEFORE requirements (within some bounds), and to avoid prefetching nonaccessed memory. TODO -- actually implement peeling. - + 6) We actually emit the prefetch instructions. ??? Perhaps emit the prefetch instructions with guards in cases where 5) was not sufficient to satisfy the constraints? + A cost model is implemented to determine whether or not prefetching is + profitable for a given loop. The cost model has three heuristics: + + 1. Function trip_count_to_ahead_ratio_too_small_p implements a + heuristic that determines whether or not the loop has too few + iterations (compared to ahead). Prefetching is not likely to be + beneficial if the trip count to ahead ratio is below a certain + minimum. + + 2. Function mem_ref_count_reasonable_p implements a heuristic that + determines whether the given loop has enough CPU ops that can be + overlapped with cache missing memory ops. If not, the loop + won't benefit from prefetching. In the implementation, + prefetching is not considered beneficial if the ratio between + the instruction count and the mem ref count is below a certain + minimum. + + 3. Function insn_to_prefetch_ratio_too_small_p implements a + heuristic that disables prefetching in a loop if the prefetching + cost is above a certain limit. The relative prefetching cost is + estimated by taking the ratio between the prefetch count and the + total intruction count (this models the I-cache cost). + + The limits used in these heuristics are defined as parameters with + reasonable default values. Machine-specific default values will be + added later. + Some other TODO: -- write and use more general reuse analysis (that could be also used in other cache aimed loop optimizations) @@ -157,7 +184,7 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA /* In some cases we are only able to determine that there is a certain probability that the two accesses hit the same cache line. In this case, we issue the prefetches for both of them if this probability - is less then (1000 - ACCEPTABLE_MISS_RATE) promile. */ + is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ #ifndef ACCEPTABLE_MISS_RATE #define ACCEPTABLE_MISS_RATE 50 @@ -167,9 +194,8 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA #define HAVE_prefetch 0 #endif -#define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * L1_CACHE_LINE_SIZE)) -/* TODO: Add parameter to specify L2 cache size. */ -#define L2_CACHE_SIZE_BYTES (8 * L1_CACHE_SIZE_BYTES) +#define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) +#define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) /* We consider a memory access nontemporal if it is not reused sooner than after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore @@ -185,12 +211,24 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA #define FENCE_FOLLOWING_MOVNT NULL_TREE #endif +/* It is not profitable to prefetch when the trip count is not at + least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. + For example, in a loop with a prefetch ahead distance of 10, + supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is + profitable to prefetch when the trip count is greater or equal to + 40. In that case, 30 out of the 40 iterations will benefit from + prefetching. */ + +#ifndef TRIP_COUNT_TO_AHEAD_RATIO +#define TRIP_COUNT_TO_AHEAD_RATIO 4 +#endif + /* The group of references between that reuse may occur. */ struct mem_ref_group { tree base; /* Base of the reference. */ - HOST_WIDE_INT step; /* Step of the reference. */ + tree step; /* Step of the reference. */ struct mem_ref *refs; /* References in the group. */ struct mem_ref_group *next; /* Next group of references. */ }; @@ -199,11 +237,30 @@ struct mem_ref_group #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) +/* Do not generate a prefetch if the unroll factor is significantly less + than what is required by the prefetch. This is to avoid redundant + prefetches. For example, when prefetch_mod is 16 and unroll_factor is + 2, prefetching requires unrolling the loop 16 times, but + the loop is actually unrolled twice. In this case (ratio = 8), + prefetching is not likely to be beneficial. */ + +#ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO +#define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4 +#endif + +/* Some of the prefetch computations have quadratic complexity. We want to + avoid huge compile times and, therefore, want to limit the amount of + memory references per loop where we consider prefetching. */ + +#ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP +#define PREFETCH_MAX_MEM_REFS_PER_LOOP 200 +#endif + /* The memory reference. */ struct mem_ref { - tree stmt; /* Statement in that the reference appears. */ + gimple stmt; /* Statement in that the reference appears. */ tree mem; /* The reference. */ HOST_WIDE_INT delta; /* Constant offset of the reference. */ struct mem_ref_group *group; /* The group of references it belongs to. */ @@ -234,7 +291,10 @@ dump_mem_ref (FILE *file, struct mem_ref *ref) fprintf (file, " group %p (base ", (void *) ref->group); print_generic_expr (file, ref->group->base, TDF_SLIM); fprintf (file, ", step "); - fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step); + if (cst_and_fits_in_hwi (ref->group->step)) + fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (ref->group->step)); + else + print_generic_expr (file, ref->group->step, TDF_TREE); fprintf (file, ")\n"); fprintf (file, " delta "); @@ -250,19 +310,20 @@ dump_mem_ref (FILE *file, struct mem_ref *ref) exist. */ static struct mem_ref_group * -find_or_create_group (struct mem_ref_group **groups, tree base, - HOST_WIDE_INT step) +find_or_create_group (struct mem_ref_group **groups, tree base, tree step) { struct mem_ref_group *group; for (; *groups; groups = &(*groups)->next) { - if ((*groups)->step == step + if (operand_equal_p ((*groups)->step, step, 0) && operand_equal_p ((*groups)->base, base, 0)) return *groups; - /* Keep the list of groups sorted by decreasing step. */ - if ((*groups)->step < step) + /* If step is an integer constant, keep the list of groups sorted + by decreasing step. */ + if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step) + && int_cst_value ((*groups)->step) < int_cst_value (step)) break; } @@ -280,7 +341,7 @@ find_or_create_group (struct mem_ref_group **groups, tree base, WRITE_P. The reference occurs in statement STMT. */ static void -record_ref (struct mem_ref_group *group, tree stmt, tree mem, +record_ref (struct mem_ref_group *group, gimple stmt, tree mem, HOST_WIDE_INT delta, bool write_p) { struct mem_ref **aref; @@ -346,8 +407,8 @@ release_mem_refs (struct mem_ref_group *groups) struct ar_data { struct loop *loop; /* Loop of the reference. */ - tree stmt; /* Statement of the reference. */ - HOST_WIDE_INT *step; /* Step of the memory reference. */ + gimple stmt; /* Statement of the reference. */ + tree *step; /* Step of the memory reference. */ HOST_WIDE_INT *delta; /* Offset of the memory reference. */ }; @@ -359,23 +420,16 @@ idx_analyze_ref (tree base, tree *index, void *data) { struct ar_data *ar_data = (struct ar_data *) data; tree ibase, step, stepsize; - HOST_WIDE_INT istep, idelta = 0, imult = 1; + HOST_WIDE_INT idelta = 0, imult = 1; affine_iv iv; - if (TREE_CODE (base) == MISALIGNED_INDIRECT_REF - || TREE_CODE (base) == ALIGN_INDIRECT_REF) - return false; - - if (!simple_iv (ar_data->loop, ar_data->stmt, *index, &iv, false)) + if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), + *index, &iv, true)) return false; ibase = iv.base; step = iv.step; - if (!cst_and_fits_in_hwi (step)) - return false; - istep = int_cst_value (step); - - if (TREE_CODE (ibase) == PLUS_EXPR + if (TREE_CODE (ibase) == POINTER_PLUS_EXPR && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) { idelta = int_cst_value (TREE_OPERAND (ibase, 1)); @@ -393,12 +447,18 @@ idx_analyze_ref (tree base, tree *index, void *data) if (!cst_and_fits_in_hwi (stepsize)) return false; imult = int_cst_value (stepsize); - - istep *= imult; + step = fold_build2 (MULT_EXPR, sizetype, + fold_convert (sizetype, step), + fold_convert (sizetype, stepsize)); idelta *= imult; } - *ar_data->step += istep; + if (*ar_data->step == NULL_TREE) + *ar_data->step = step; + else + *ar_data->step = fold_build2 (PLUS_EXPR, sizetype, + fold_convert (sizetype, *ar_data->step), + fold_convert (sizetype, step)); *ar_data->delta += idelta; *index = ibase; @@ -412,21 +472,29 @@ idx_analyze_ref (tree base, tree *index, void *data) static bool analyze_ref (struct loop *loop, tree *ref_p, tree *base, - HOST_WIDE_INT *step, HOST_WIDE_INT *delta, - tree stmt) + tree *step, HOST_WIDE_INT *delta, + gimple stmt) { struct ar_data ar_data; tree off; HOST_WIDE_INT bit_offset; tree ref = *ref_p; - *step = 0; + *step = NULL_TREE; *delta = 0; - /* First strip off the component references. Ignore bitfields. */ - if (TREE_CODE (ref) == COMPONENT_REF - && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1))) - ref = TREE_OPERAND (ref, 0); + /* First strip off the component references. Ignore bitfields. + Also strip off the real and imagine parts of a complex, so that + they can have the same base. */ + if (TREE_CODE (ref) == REALPART_EXPR + || TREE_CODE (ref) == IMAGPART_EXPR + || (TREE_CODE (ref) == COMPONENT_REF + && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))) + { + if (TREE_CODE (ref) == IMAGPART_EXPR) + *delta += int_size_in_bytes (TREE_TYPE (ref)); + ref = TREE_OPERAND (ref, 0); + } *ref_p = ref; @@ -435,7 +503,7 @@ analyze_ref (struct loop *loop, tree *ref_p, tree *base, off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); bit_offset = TREE_INT_CST_LOW (off); gcc_assert (bit_offset % BITS_PER_UNIT == 0); - + *delta += bit_offset / BITS_PER_UNIT; } @@ -453,14 +521,28 @@ analyze_ref (struct loop *loop, tree *ref_p, tree *base, static bool gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, - tree ref, bool write_p, tree stmt) + tree ref, bool write_p, gimple stmt) { - tree base; - HOST_WIDE_INT step, delta; + tree base, step; + HOST_WIDE_INT delta; struct mem_ref_group *agrp; + if (get_base_address (ref) == NULL) + return false; + if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) return false; + /* If analyze_ref fails the default is a NULL_TREE. We can stop here. */ + if (step == NULL_TREE) + return false; + + /* Stop if the address of BASE could not be taken. */ + if (may_be_nonaddressable_p (base)) + return false; + + /* Limit non-constant step prefetching only to the innermost loops. */ + if (!cst_and_fits_in_hwi (step) && loop->inner != NULL) + return false; /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP are integer constants. */ @@ -474,16 +556,18 @@ gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, true if there are no other memory references inside the loop. */ static struct mem_ref_group * -gather_memory_references (struct loop *loop, bool *no_other_refs) +gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) { basic_block *body = get_loop_body_in_dom_order (loop); basic_block bb; unsigned i; - block_stmt_iterator bsi; - tree stmt, lhs, rhs, call; + gimple_stmt_iterator bsi; + gimple stmt; + tree lhs, rhs; struct mem_ref_group *refs = NULL; *no_other_refs = true; + *ref_count = 0; /* Scan the loop body in order, so that the former references precede the later ones. */ @@ -493,29 +577,34 @@ gather_memory_references (struct loop *loop, bool *no_other_refs) if (bb->loop_father != loop) continue; - for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) + for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) { - stmt = bsi_stmt (bsi); - call = get_call_expr_in (stmt); - if (call && !(call_expr_flags (call) & ECF_CONST)) - *no_other_refs = false; + stmt = gsi_stmt (bsi); - if (TREE_CODE (stmt) != GIMPLE_MODIFY_STMT) + if (gimple_code (stmt) != GIMPLE_ASSIGN) { - if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)) + if (gimple_vuse (stmt) + || (is_gimple_call (stmt) + && !(gimple_call_flags (stmt) & ECF_CONST))) *no_other_refs = false; continue; } - lhs = GIMPLE_STMT_OPERAND (stmt, 0); - rhs = GIMPLE_STMT_OPERAND (stmt, 1); + lhs = gimple_assign_lhs (stmt); + rhs = gimple_assign_rhs1 (stmt); if (REFERENCE_CLASS_P (rhs)) + { *no_other_refs &= gather_memory_references_ref (loop, &refs, rhs, false, stmt); + *ref_count += 1; + } if (REFERENCE_CLASS_P (lhs)) + { *no_other_refs &= gather_memory_references_ref (loop, &refs, lhs, true, stmt); + *ref_count += 1; + } } } free (body); @@ -528,8 +617,16 @@ gather_memory_references (struct loop *loop, bool *no_other_refs) static void prune_ref_by_self_reuse (struct mem_ref *ref) { - HOST_WIDE_INT step = ref->group->step; - bool backward = step < 0; + HOST_WIDE_INT step; + bool backward; + + /* If the step size is non constant, we cannot calculate prefetch_mod. */ + if (!cst_and_fits_in_hwi (ref->group->step)) + return; + + step = int_cst_value (ref->group->step); + + backward = step < 0; if (step == 0) { @@ -567,6 +664,54 @@ ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) return (x + by - 1) / by; } +/* Given a CACHE_LINE_SIZE and two inductive memory references + with a common STEP greater than CACHE_LINE_SIZE and an address + difference DELTA, compute the probability that they will fall + in different cache lines. Return true if the computed miss rate + is not greater than the ACCEPTABLE_MISS_RATE. DISTINCT_ITERS is the + number of distinct iterations after which the pattern repeats itself. + ALIGN_UNIT is the unit of alignment in bytes. */ + +static bool +is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size, + HOST_WIDE_INT step, HOST_WIDE_INT delta, + unsigned HOST_WIDE_INT distinct_iters, + int align_unit) +{ + unsigned align, iter; + int total_positions, miss_positions, max_allowed_miss_positions; + int address1, address2, cache_line1, cache_line2; + + /* It always misses if delta is greater than or equal to the cache + line size. */ + if (delta >= (HOST_WIDE_INT) cache_line_size) + return false; + + miss_positions = 0; + total_positions = (cache_line_size / align_unit) * distinct_iters; + max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000; + + /* Iterate through all possible alignments of the first + memory reference within its cache line. */ + for (align = 0; align < cache_line_size; align += align_unit) + + /* Iterate through all distinct iterations. */ + for (iter = 0; iter < distinct_iters; iter++) + { + address1 = align + step * iter; + address2 = address1 + delta; + cache_line1 = address1 / cache_line_size; + cache_line2 = address2 / cache_line_size; + if (cache_line1 != cache_line2) + { + miss_positions += 1; + if (miss_positions > max_allowed_miss_positions) + return false; + } + } + return true; +} + /* Prune the prefetch candidate REF using the reuse with BY. If BY_IS_BEFORE is true, BY is before REF in the loop. */ @@ -574,12 +719,26 @@ static void prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, bool by_is_before) { - HOST_WIDE_INT step = ref->group->step; - bool backward = step < 0; + HOST_WIDE_INT step; + bool backward; HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; HOST_WIDE_INT delta = delta_b - delta_r; HOST_WIDE_INT hit_from; unsigned HOST_WIDE_INT prefetch_before, prefetch_block; + HOST_WIDE_INT reduced_step; + unsigned HOST_WIDE_INT reduced_prefetch_block; + tree ref_type; + int align_unit; + + /* If the step is non constant we cannot calculate prefetch_before. */ + if (!cst_and_fits_in_hwi (ref->group->step)) { + return; + } + + step = int_cst_value (ref->group->step); + + backward = step < 0; + if (delta == 0) { @@ -587,7 +746,7 @@ prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, former. */ if (by_is_before) ref->prefetch_before = 0; - + return; } @@ -635,32 +794,41 @@ prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; prefetch_before = (hit_from - delta_r + step - 1) / step; + /* Do not reduce prefetch_before if we meet beyond cache size. */ + if (prefetch_before > absu_hwi (L2_CACHE_SIZE_BYTES / step)) + prefetch_before = PREFETCH_ALL; if (prefetch_before < ref->prefetch_before) ref->prefetch_before = prefetch_before; return; } - /* A more complicated case. First let us ensure that size of cache line - and step are coprime (here we assume that PREFETCH_BLOCK is a power - of two. */ + /* A more complicated case with step > prefetch_block. First reduce + the ratio between the step and the cache line size to its simplest + terms. The resulting denominator will then represent the number of + distinct iterations after which each address will go back to its + initial location within the cache line. This computation assumes + that PREFETCH_BLOCK is a power of two. */ prefetch_block = PREFETCH_BLOCK; - while ((step & 1) == 0 - && prefetch_block > 1) + reduced_prefetch_block = prefetch_block; + reduced_step = step; + while ((reduced_step & 1) == 0 + && reduced_prefetch_block > 1) { - step >>= 1; - prefetch_block >>= 1; - delta >>= 1; + reduced_step >>= 1; + reduced_prefetch_block >>= 1; } - /* Now step > prefetch_block, and step and prefetch_block are coprime. - Determine the probability that the accesses hit the same cache line. */ - prefetch_before = delta / step; delta %= step; - if ((unsigned HOST_WIDE_INT) delta - <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000)) + ref_type = TREE_TYPE (ref->mem); + align_unit = TYPE_ALIGN (ref_type) / 8; + if (is_miss_rate_acceptable (prefetch_block, step, delta, + reduced_prefetch_block, align_unit)) { + /* Do not reduce prefetch_before if we meet beyond cache size. */ + if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK) + prefetch_before = PREFETCH_ALL; if (prefetch_before < ref->prefetch_before) ref->prefetch_before = prefetch_before; @@ -670,8 +838,8 @@ prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, /* Try also the following iteration. */ prefetch_before++; delta = step - delta; - if ((unsigned HOST_WIDE_INT) delta - <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000)) + if (is_miss_rate_acceptable (prefetch_block, step, delta, + reduced_prefetch_block, align_unit)) { if (prefetch_before < ref->prefetch_before) ref->prefetch_before = prefetch_before; @@ -774,11 +942,20 @@ should_issue_prefetch_p (struct mem_ref *ref) /* For now do not issue prefetches for only first few of the iterations. */ if (ref->prefetch_before != PREFETCH_ALL) - return false; + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ignoring %p due to prefetch_before\n", + (void *) ref); + return false; + } /* Do not prefetch nontemporal stores. */ if (ref->storent_p) - return false; + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ignoring nontemporal store %p\n", (void *) ref); + return false; + } return true; } @@ -820,6 +997,12 @@ schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, if (!should_issue_prefetch_p (ref)) continue; + /* The loop is far from being sufficiently unrolled for this + prefetch. Do not generate prefetch to avoid many redudant + prefetches. */ + if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) + continue; + /* 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 @@ -844,20 +1027,42 @@ schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, return any; } -/* Determine whether there is any reference suitable for prefetching - in GROUPS. */ +/* Return TRUE if no prefetch is going to be generated in the given + GROUPS. */ static bool -anything_to_prefetch_p (struct mem_ref_group *groups) +nothing_to_prefetch_p (struct mem_ref_group *groups) { struct mem_ref *ref; for (; groups; groups = groups->next) for (ref = groups->refs; ref; ref = ref->next) if (should_issue_prefetch_p (ref)) - return true; + return false; - return false; + return true; +} + +/* Estimate the number of prefetches in the given GROUPS. + UNROLL_FACTOR is the factor by which LOOP was unrolled. */ + +static int +estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor) +{ + struct mem_ref *ref; + unsigned n_prefetches; + int prefetch_count = 0; + + for (; groups; groups = groups->next) + for (ref = groups->refs; ref; ref = ref->next) + if (should_issue_prefetch_p (ref)) + { + n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) + / ref->prefetch_mod); + prefetch_count += n_prefetches; + } + + return prefetch_count; } /* Issue prefetches for the reference REF into loop as decided before. @@ -868,8 +1073,9 @@ static void issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) { HOST_WIDE_INT delta; - tree addr, addr_base, prefetch, write_p, local; - block_stmt_iterator bsi; + tree addr, addr_base, write_p, local, forward; + gimple prefetch; + gimple_stmt_iterator bsi; unsigned n_prefetches, ap; bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; @@ -878,27 +1084,42 @@ issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) nontemporal ? " nontemporal" : "", (void *) ref); - bsi = bsi_for_stmt (ref->stmt); + bsi = gsi_for_stmt (ref->stmt); n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) / 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); + addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), + true, NULL, true, GSI_SAME_STMT); write_p = ref->write_p ? integer_one_node : integer_zero_node; - local = build_int_cst (integer_type_node, nontemporal ? 0 : 3); + local = nontemporal ? integer_zero_node : integer_three_node; for (ap = 0; ap < n_prefetches; ap++) { - /* Determine the address to prefetch. */ - delta = (ahead + ap * ref->prefetch_mod) * ref->group->step; - addr = fold_build2 (PLUS_EXPR, ptr_type_node, - addr_base, build_int_cst (ptr_type_node, delta)); - addr = force_gimple_operand_bsi (&bsi, unshare_expr (addr), true, NULL); - + if (cst_and_fits_in_hwi (ref->group->step)) + { + /* Determine the address to prefetch. */ + delta = (ahead + ap * ref->prefetch_mod) * + int_cst_value (ref->group->step); + addr = fold_build_pointer_plus_hwi (addr_base, delta); + addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, + true, GSI_SAME_STMT); + } + else + { + /* The step size is non-constant but loop-invariant. We use the + heuristic to simply prefetch ahead iterations ahead. */ + forward = fold_build2 (MULT_EXPR, sizetype, + fold_convert (sizetype, ref->group->step), + fold_convert (sizetype, size_int (ahead))); + addr = fold_build_pointer_plus (addr_base, forward); + addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, + NULL, true, GSI_SAME_STMT); + } /* Create the prefetch instruction. */ - prefetch = build_call_expr (built_in_decls[BUILT_IN_PREFETCH], - 3, addr, write_p, local); - bsi_insert_before (&bsi, prefetch, BSI_SAME_STMT); + prefetch = gimple_build_call (builtin_decl_explicit (BUILT_IN_PREFETCH), + 3, addr, write_p, local); + gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); } } @@ -940,7 +1161,7 @@ nontemporal_store_p (struct mem_ref *ref) if (mode == BLKmode) return false; - code = storent_optab->handlers[mode].insn_code; + code = optab_handler (storent_optab, mode); return code != CODE_FOR_nothing; } @@ -957,7 +1178,7 @@ mark_nontemporal_store (struct mem_ref *ref) fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", (void *) ref); - MOVE_NONTEMPORAL (ref->stmt) = true; + gimple_assign_set_nontemporal_move (ref->stmt, true); ref->storent_p = true; return true; @@ -970,22 +1191,22 @@ emit_mfence_after_loop (struct loop *loop) { VEC (edge, heap) *exits = get_loop_exit_edges (loop); edge exit; - tree call; - block_stmt_iterator bsi; + gimple call; + gimple_stmt_iterator bsi; unsigned i; - for (i = 0; VEC_iterate (edge, exits, i, exit); i++) + FOR_EACH_VEC_ELT (edge, exits, i, exit) { - call = build_function_call_expr (FENCE_FOLLOWING_MOVNT, NULL_TREE); + call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); if (!single_pred_p (exit->dest) /* If possible, we prefer not to insert the fence on other paths in cfg. */ && !(exit->flags & EDGE_ABNORMAL)) split_loop_exit_edge (exit); - bsi = bsi_after_labels (exit->dest); + bsi = gsi_after_labels (exit->dest); - bsi_insert_before (&bsi, call, BSI_NEW_STMT); + gsi_insert_before (&bsi, call, GSI_NEW_STMT); mark_virtual_ops_for_renaming (call); } @@ -1011,7 +1232,7 @@ may_use_storent_in_loop_p (struct loop *loop) unsigned i; edge exit; - for (i = 0; VEC_iterate (edge, exits, i, exit); i++) + FOR_EACH_VEC_ELT (edge, exits, i, exit) if ((exit->flags & EDGE_ABNORMAL) && exit->dest == EXIT_BLOCK_PTR) ret = false; @@ -1230,13 +1451,13 @@ self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, strides = XCNEWVEC (HOST_WIDE_INT, n); access_fns = DR_ACCESS_FNS (dr); - for (i = 0; VEC_iterate (tree, access_fns, i, access_fn); i++) + FOR_EACH_VEC_ELT (tree, access_fns, i, access_fn) { /* Keep track of the reference corresponding to the subscript, so that we know its stride. */ while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) ref = TREE_OPERAND (ref, 0); - + if (TREE_CODE (ref) == ARRAY_REF) { stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); @@ -1327,20 +1548,21 @@ determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, continue; aloop = VEC_index (loop_p, vloops, i); - vol = estimated_loop_iterations_int (aloop, false); + vol = max_stmt_executions_int (aloop, false); if (vol < 0) vol = expected_loop_iterations (aloop); volume *= vol; } /* Prepare the references in the form suitable for data dependence - analysis. We ignore unanalysable data references (the results + analysis. We ignore unanalyzable data references (the results are used just as a heuristics to estimate temporality of the references, hence we do not need to worry about correctness). */ for (gr = refs; gr; gr = gr->next) for (ref = gr->refs; ref; ref = ref->next) { - dr = create_data_ref (nest, ref->mem, ref->stmt, !ref->write_p); + dr = create_data_ref (nest, loop_containing_stmt (ref->stmt), + ref->mem, ref->stmt, !ref->write_p); if (dr) { @@ -1352,10 +1574,10 @@ determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, no_other_refs = false; } - for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++) + FOR_EACH_VEC_ELT (data_reference_p, datarefs, i, dr) { dist = self_reuse_distance (dr, loop_data_size, n, loop); - ref = dr->aux; + ref = (struct mem_ref *) dr->aux; if (ref->reuse_distance > dist) ref->reuse_distance = dist; @@ -1365,27 +1587,27 @@ determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, compute_all_dependences (datarefs, &dependences, vloops, true); - for (i = 0; VEC_iterate (ddr_p, dependences, i, dep); i++) + FOR_EACH_VEC_ELT (ddr_p, dependences, i, dep) { if (DDR_ARE_DEPENDENT (dep) == chrec_known) continue; - ref = DDR_A (dep)->aux; - refb = DDR_B (dep)->aux; + ref = (struct mem_ref *) DDR_A (dep)->aux; + refb = (struct mem_ref *) DDR_B (dep)->aux; if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know || DDR_NUM_DIST_VECTS (dep) == 0) { - /* If the dependence cannot be analysed, assume that there might be + /* If the dependence cannot be analyzed, assume that there might be a reuse. */ dist = 0; - + ref->independent_p = false; refb->independent_p = false; } else { - /* The distance vectors are normalised to be always lexicographically + /* The distance vectors are normalized to be always lexicographically positive, hence we cannot tell just from them whether DDR_A comes before DDR_B or vice versa. However, it is not important, anyway -- if DDR_A is close to DDR_B, then it is either reused in @@ -1444,6 +1666,112 @@ determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, } } +/* Determine whether or not the trip count to ahead ratio is too small based + on prefitablility consideration. + AHEAD: the iteration ahead distance, + EST_NITER: the estimated trip count. */ + +static bool +trip_count_to_ahead_ratio_too_small_p (unsigned ahead, HOST_WIDE_INT est_niter) +{ + /* Assume trip count to ahead ratio is big enough if the trip count could not + be estimated at compile time. */ + if (est_niter < 0) + return false; + + if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- loop estimated to roll only %d times\n", + (int) est_niter); + return true; + } + + return false; +} + +/* Determine whether or not the number of memory references in the loop is + reasonable based on the profitablity and compilation time considerations. + NINSNS: estimated number of instructions in the loop, + MEM_REF_COUNT: total number of memory references in the loop. */ + +static bool +mem_ref_count_reasonable_p (unsigned ninsns, unsigned mem_ref_count) +{ + int insn_to_mem_ratio; + + if (mem_ref_count == 0) + return false; + + /* Miss rate computation (is_miss_rate_acceptable) and dependence analysis + (compute_all_dependences) have high costs based on quadratic complexity. + To avoid huge compilation time, we give up prefetching if mem_ref_count + is too large. */ + if (mem_ref_count > PREFETCH_MAX_MEM_REFS_PER_LOOP) + return false; + + /* Prefetching improves performance by overlapping cache missing + memory accesses with CPU operations. If the loop does not have + enough CPU operations to overlap with memory operations, prefetching + won't give a significant benefit. One approximate way of checking + this is to require the ratio of instructions to memory references to + be above a certain limit. This approximation works well in practice. + TODO: Implement a more precise computation by estimating the time + for each CPU or memory op in the loop. Time estimates for memory ops + should account for cache misses. */ + insn_to_mem_ratio = ninsns / mem_ref_count; + + if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- instruction to memory reference ratio (%d) too small\n", + insn_to_mem_ratio); + return false; + } + + return true; +} + +/* Determine whether or not the instruction to prefetch ratio in the loop is + too small based on the profitablity consideration. + NINSNS: estimated number of instructions in the loop, + PREFETCH_COUNT: an estimate of the number of prefetches, + UNROLL_FACTOR: the factor to unroll the loop if prefetching. */ + +static bool +insn_to_prefetch_ratio_too_small_p (unsigned ninsns, unsigned prefetch_count, + unsigned unroll_factor) +{ + int insn_to_prefetch_ratio; + + /* Prefetching most likely causes performance degradation when the instruction + to prefetch ratio is too small. Too many prefetch instructions in a loop + may reduce the I-cache performance. + (unroll_factor * ninsns) is used to estimate the number of instructions in + the unrolled loop. This implementation is a bit simplistic -- the number + of issued prefetch instructions is also affected by unrolling. So, + prefetch_mod and the unroll factor should be taken into account when + determining prefetch_count. Also, the number of insns of the unrolled + loop will usually be significantly smaller than the number of insns of the + original loop * unroll_factor (at least the induction variable increases + and the exit branches will get eliminated), so it might be better to use + tree_estimate_loop_size + estimated_unrolled_size. */ + insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count; + if (insn_to_prefetch_ratio < MIN_INSN_TO_PREFETCH_RATIO) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Not prefetching -- instruction to prefetch ratio (%d) too small\n", + insn_to_prefetch_ratio); + return true; + } + + return false; +} + + /* Issue prefetch instructions for array references in LOOP. Returns true if the LOOP was unrolled. */ @@ -1455,53 +1783,73 @@ loop_prefetch_arrays (struct loop *loop) HOST_WIDE_INT est_niter; struct tree_niter_desc desc; bool unrolled = false, no_other_refs; + unsigned prefetch_count; + unsigned mem_ref_count; - if (!maybe_hot_bb_p (loop->header)) + if (optimize_loop_nest_for_size_p (loop)) { if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, " ignored (cold area)\n"); return false; } + /* 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); + if (time == 0) + return false; + + ahead = (PREFETCH_LATENCY + time - 1) / time; + est_niter = max_stmt_executions_int (loop, false); + + /* Prefetching is not likely to be profitable if the trip count to ahead + ratio is too small. */ + if (trip_count_to_ahead_ratio_too_small_p (ahead, est_niter)) + return false; + + ninsns = tree_num_loop_insns (loop, &eni_size_weights); + /* Step 1: gather the memory references. */ - refs = gather_memory_references (loop, &no_other_refs); + refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); + + /* Give up prefetching if the number of memory references in the + loop is not reasonable based on profitablity and compilation time + considerations. */ + if (!mem_ref_count_reasonable_p (ninsns, mem_ref_count)) + goto fail; /* Step 2: estimate the reuse effects. */ prune_by_reuse (refs); - if (!anything_to_prefetch_p (refs)) + if (nothing_to_prefetch_p (refs)) goto fail; determine_loop_nest_reuse (loop, refs, no_other_refs); - /* Step 3: determine the ahead and unroll factor. */ + /* Step 3: determine unroll factor. */ + unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, + est_niter); - /* 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); + /* Estimate prefetch count for the unrolled loop. */ + prefetch_count = estimate_prefetch_count (refs, unroll_factor); + if (prefetch_count == 0) + goto fail; - /* 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; - } + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " + HOST_WIDE_INT_PRINT_DEC "\n" + "insn count %d, mem ref count %d, prefetch count %d\n", + ahead, unroll_factor, est_niter, + ninsns, mem_ref_count, prefetch_count); + + /* Prefetching is not likely to be profitable if the instruction to prefetch + ratio is too small. */ + if (insn_to_prefetch_ratio_too_small_p (ninsns, prefetch_count, + unroll_factor)) + goto fail; mark_nontemporal_stores (loop, refs); - 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); - /* Step 4: what to prefetch? */ if (!schedule_prefetches (refs, unroll_factor, ahead)) goto fail; @@ -1548,26 +1896,28 @@ tree_ssa_prefetch_arrays (void) SIMULTANEOUS_PREFETCHES); fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); - fprintf (dump_file, " L1 cache size: %d lines, %d bytes\n", - L1_CACHE_SIZE, L1_CACHE_SIZE_BYTES); + fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", + L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); - fprintf (dump_file, " L2 cache size: %d bytes\n", L2_CACHE_SIZE_BYTES); + fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); + fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", + MIN_INSN_TO_PREFETCH_RATIO); + fprintf (dump_file, " min insn-to-mem ratio: %d \n", + PREFETCH_MIN_INSN_TO_MEM_RATIO); fprintf (dump_file, "\n"); } initialize_original_copy_tables (); - if (!built_in_decls[BUILT_IN_PREFETCH]) + if (!builtin_decl_explicit_p (BUILT_IN_PREFETCH)) { - tree type = build_function_type (void_type_node, - tree_cons (NULL_TREE, - const_ptr_type_node, - NULL_TREE)); + tree type = build_function_type_list (void_type_node, + const_ptr_type_node, 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; + set_builtin_decl (BUILT_IN_PREFETCH, decl, false); } /* We assume that size of cache line is a power of two, so verify this