+++ /dev/null
-/* Dead and redundant store elimination
- Copyright (C) 2004-2019 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 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 COPYING3. If not see
-<http://www.gnu.org/licenses/>. */
-
-#include "config.h"
-#include "system.h"
-#include "coretypes.h"
-#include "backend.h"
-#include "rtl.h"
-#include "tree.h"
-#include "gimple.h"
-#include "tree-pass.h"
-#include "ssa.h"
-#include "gimple-pretty-print.h"
-#include "fold-const.h"
-#include "gimple-iterator.h"
-#include "tree-cfg.h"
-#include "tree-dfa.h"
-#include "domwalk.h"
-#include "tree-cfgcleanup.h"
-#include "params.h"
-#include "alias.h"
-#include "tree-ssa-loop.h"
-#include "tree-ssa-dse.h"
-
-/* This file implements dead store elimination.
-
- A dead store is a store into a memory location which will later be
- overwritten by another store without any intervening loads. In this
- case the earlier store can be deleted or trimmed if the store
- was partially dead.
-
- A redundant store is a store into a memory location which stores
- the exact same value as a prior store to the same memory location.
- While this can often be handled by dead store elimination, removing
- the redundant store is often better than removing or trimming the
- dead store.
-
- In our SSA + virtual operand world we use immediate uses of virtual
- operands to detect these cases. If a store's virtual definition
- is used precisely once by a later store to the same location which
- post dominates the first store, then the first store is dead. If
- the data stored is the same, then the second store is redundant.
-
- The single use of the store's virtual definition ensures that
- there are no intervening aliased loads and the requirement that
- the second load post dominate the first ensures that if the earlier
- store executes, then the later stores will execute before the function
- exits.
-
- It may help to think of this as first moving the earlier store to
- the point immediately before the later store. Again, the single
- use of the virtual definition and the post-dominance relationship
- ensure that such movement would be safe. Clearly if there are
- back to back stores, then the second is makes the first dead. If
- the second store stores the same value, then the second store is
- redundant.
-
- Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
- may also help in understanding this code since it discusses the
- relationship between dead store and redundant load elimination. In
- fact, they are the same transformation applied to different views of
- the CFG. */
-
-static void delete_dead_or_redundant_call (gimple_stmt_iterator *, const char *);
-
-/* Bitmap of blocks that have had EH statements cleaned. We should
- remove their dead edges eventually. */
-static bitmap need_eh_cleanup;
-
-/* STMT is a statement that may write into memory. Analyze it and
- initialize WRITE to describe how STMT affects memory.
-
- Return TRUE if the the statement was analyzed, FALSE otherwise.
-
- It is always safe to return FALSE. But typically better optimziation
- can be achieved by analyzing more statements. */
-
-static bool
-initialize_ao_ref_for_dse (gimple *stmt, ao_ref *write)
-{
- /* It's advantageous to handle certain mem* functions. */
- if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
- {
- switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
- {
- case BUILT_IN_MEMCPY:
- case BUILT_IN_MEMMOVE:
- case BUILT_IN_MEMSET:
- case BUILT_IN_MEMCPY_CHK:
- case BUILT_IN_MEMMOVE_CHK:
- case BUILT_IN_MEMSET_CHK:
- case BUILT_IN_STRNCPY:
- case BUILT_IN_STRNCPY_CHK:
- {
- tree size = gimple_call_arg (stmt, 2);
- tree ptr = gimple_call_arg (stmt, 0);
- ao_ref_init_from_ptr_and_size (write, ptr, size);
- return true;
- }
-
- /* A calloc call can never be dead, but it can make
- subsequent stores redundant if they store 0 into
- the same memory locations. */
- case BUILT_IN_CALLOC:
- {
- tree nelem = gimple_call_arg (stmt, 0);
- tree selem = gimple_call_arg (stmt, 1);
- tree lhs;
- if (TREE_CODE (nelem) == INTEGER_CST
- && TREE_CODE (selem) == INTEGER_CST
- && (lhs = gimple_call_lhs (stmt)) != NULL_TREE)
- {
- tree size = fold_build2 (MULT_EXPR, TREE_TYPE (nelem),
- nelem, selem);
- ao_ref_init_from_ptr_and_size (write, lhs, size);
- return true;
- }
- }
-
- default:
- break;
- }
- }
- else if (is_gimple_assign (stmt))
- {
- ao_ref_init (write, gimple_assign_lhs (stmt));
- return true;
- }
- return false;
-}
-
-/* Given REF from the the alias oracle, return TRUE if it is a valid
- memory reference for dead store elimination, false otherwise.
-
- In particular, the reference must have a known base, known maximum
- size, start at a byte offset and have a size that is one or more
- bytes. */
-
-static bool
-valid_ao_ref_for_dse (ao_ref *ref)
-{
- return (ao_ref_base (ref)
- && known_size_p (ref->max_size)
- && maybe_ne (ref->size, 0)
- && known_eq (ref->max_size, ref->size)
- && known_ge (ref->offset, 0)
- && multiple_p (ref->offset, BITS_PER_UNIT)
- && multiple_p (ref->size, BITS_PER_UNIT));
-}
-
-/* Try to normalize COPY (an ao_ref) relative to REF. Essentially when we are
- done COPY will only refer bytes found within REF. Return true if COPY
- is known to intersect at least one byte of REF. */
-
-static bool
-normalize_ref (ao_ref *copy, ao_ref *ref)
-{
- if (!ordered_p (copy->offset, ref->offset))
- return false;
-
- /* If COPY starts before REF, then reset the beginning of
- COPY to match REF and decrease the size of COPY by the
- number of bytes removed from COPY. */
- if (maybe_lt (copy->offset, ref->offset))
- {
- poly_int64 diff = ref->offset - copy->offset;
- if (maybe_le (copy->size, diff))
- return false;
- copy->size -= diff;
- copy->offset = ref->offset;
- }
-
- poly_int64 diff = copy->offset - ref->offset;
- if (maybe_le (ref->size, diff))
- return false;
-
- /* If COPY extends beyond REF, chop off its size appropriately. */
- poly_int64 limit = ref->size - diff;
- if (!ordered_p (limit, copy->size))
- return false;
-
- if (maybe_gt (copy->size, limit))
- copy->size = limit;
- return true;
-}
-
-/* Clear any bytes written by STMT from the bitmap LIVE_BYTES. The base
- address written by STMT must match the one found in REF, which must
- have its base address previously initialized.
-
- This routine must be conservative. If we don't know the offset or
- actual size written, assume nothing was written. */
-
-static void
-clear_bytes_written_by (sbitmap live_bytes, gimple *stmt, ao_ref *ref)
-{
- ao_ref write;
- if (!initialize_ao_ref_for_dse (stmt, &write))
- return;
-
- /* Verify we have the same base memory address, the write
- has a known size and overlaps with REF. */
- HOST_WIDE_INT start, size;
- if (valid_ao_ref_for_dse (&write)
- && operand_equal_p (write.base, ref->base, OEP_ADDRESS_OF)
- && known_eq (write.size, write.max_size)
- && normalize_ref (&write, ref)
- && (write.offset - ref->offset).is_constant (&start)
- && write.size.is_constant (&size))
- bitmap_clear_range (live_bytes, start / BITS_PER_UNIT,
- size / BITS_PER_UNIT);
-}
-
-/* REF is a memory write. Extract relevant information from it and
- initialize the LIVE_BYTES bitmap. If successful, return TRUE.
- Otherwise return FALSE. */
-
-static bool
-setup_live_bytes_from_ref (ao_ref *ref, sbitmap live_bytes)
-{
- HOST_WIDE_INT const_size;
- if (valid_ao_ref_for_dse (ref)
- && ref->size.is_constant (&const_size)
- && (const_size / BITS_PER_UNIT
- <= param_dse_max_object_size))
- {
- bitmap_clear (live_bytes);
- bitmap_set_range (live_bytes, 0, const_size / BITS_PER_UNIT);
- return true;
- }
- return false;
-}
-
-/* Compute the number of elements that we can trim from the head and
- tail of ORIG resulting in a bitmap that is a superset of LIVE.
-
- Store the number of elements trimmed from the head and tail in
- TRIM_HEAD and TRIM_TAIL.
-
- STMT is the statement being trimmed and is used for debugging dump
- output only. */
-
-static void
-compute_trims (ao_ref *ref, sbitmap live, int *trim_head, int *trim_tail,
- gimple *stmt)
-{
- /* We use sbitmaps biased such that ref->offset is bit zero and the bitmap
- extends through ref->size. So we know that in the original bitmap
- bits 0..ref->size were true. We don't actually need the bitmap, just
- the REF to compute the trims. */
-
- /* Now identify how much, if any of the tail we can chop off. */
- HOST_WIDE_INT const_size;
- int last_live = bitmap_last_set_bit (live);
- if (ref->size.is_constant (&const_size))
- {
- int last_orig = (const_size / BITS_PER_UNIT) - 1;
- /* We can leave inconvenient amounts on the tail as
- residual handling in mem* and str* functions is usually
- reasonably efficient. */
- *trim_tail = last_orig - last_live;
-
- /* But don't trim away out of bounds accesses, as this defeats
- proper warnings.
-
- We could have a type with no TYPE_SIZE_UNIT or we could have a VLA
- where TYPE_SIZE_UNIT is not a constant. */
- if (*trim_tail
- && TYPE_SIZE_UNIT (TREE_TYPE (ref->base))
- && TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (ref->base))) == INTEGER_CST
- && compare_tree_int (TYPE_SIZE_UNIT (TREE_TYPE (ref->base)),
- last_orig) <= 0)
- *trim_tail = 0;
- }
- else
- *trim_tail = 0;
-
- /* Identify how much, if any of the head we can chop off. */
- int first_orig = 0;
- int first_live = bitmap_first_set_bit (live);
- *trim_head = first_live - first_orig;
-
- /* If more than a word remains, then make sure to keep the
- starting point at least word aligned. */
- if (last_live - first_live > UNITS_PER_WORD)
- *trim_head &= ~(UNITS_PER_WORD - 1);
-
- if ((*trim_head || *trim_tail)
- && dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Trimming statement (head = %d, tail = %d): ",
- *trim_head, *trim_tail);
- print_gimple_stmt (dump_file, stmt, 0, dump_flags);
- fprintf (dump_file, "\n");
- }
-}
-
-/* STMT initializes an object from COMPLEX_CST where one or more of the
- bytes written may be dead stores. REF is a representation of the
- memory written. LIVE is the bitmap of stores that are actually live.
-
- Attempt to rewrite STMT so that only the real or imaginary part of
- the object is actually stored. */
-
-static void
-maybe_trim_complex_store (ao_ref *ref, sbitmap live, gimple *stmt)
-{
- int trim_head, trim_tail;
- compute_trims (ref, live, &trim_head, &trim_tail, stmt);
-
- /* The amount of data trimmed from the head or tail must be at
- least half the size of the object to ensure we're trimming
- the entire real or imaginary half. By writing things this
- way we avoid more O(n) bitmap operations. */
- if (known_ge (trim_tail * 2 * BITS_PER_UNIT, ref->size))
- {
- /* TREE_REALPART is live */
- tree x = TREE_REALPART (gimple_assign_rhs1 (stmt));
- tree y = gimple_assign_lhs (stmt);
- y = build1 (REALPART_EXPR, TREE_TYPE (x), y);
- gimple_assign_set_lhs (stmt, y);
- gimple_assign_set_rhs1 (stmt, x);
- }
- else if (known_ge (trim_head * 2 * BITS_PER_UNIT, ref->size))
- {
- /* TREE_IMAGPART is live */
- tree x = TREE_IMAGPART (gimple_assign_rhs1 (stmt));
- tree y = gimple_assign_lhs (stmt);
- y = build1 (IMAGPART_EXPR, TREE_TYPE (x), y);
- gimple_assign_set_lhs (stmt, y);
- gimple_assign_set_rhs1 (stmt, x);
- }
-
- /* Other cases indicate parts of both the real and imag subobjects
- are live. We do not try to optimize those cases. */
-}
-
-/* STMT initializes an object using a CONSTRUCTOR where one or more of the
- bytes written are dead stores. ORIG is the bitmap of bytes stored by
- STMT. LIVE is the bitmap of stores that are actually live.
-
- Attempt to rewrite STMT so that only the real or imaginary part of
- the object is actually stored.
-
- The most common case for getting here is a CONSTRUCTOR with no elements
- being used to zero initialize an object. We do not try to handle other
- cases as those would force us to fully cover the object with the
- CONSTRUCTOR node except for the components that are dead. */
-
-static void
-maybe_trim_constructor_store (ao_ref *ref, sbitmap live, gimple *stmt)
-{
- tree ctor = gimple_assign_rhs1 (stmt);
-
- /* This is the only case we currently handle. It actually seems to
- catch most cases of actual interest. */
- gcc_assert (CONSTRUCTOR_NELTS (ctor) == 0);
-
- int head_trim = 0;
- int tail_trim = 0;
- compute_trims (ref, live, &head_trim, &tail_trim, stmt);
-
- /* Now we want to replace the constructor initializer
- with memset (object + head_trim, 0, size - head_trim - tail_trim). */
- if (head_trim || tail_trim)
- {
- /* We want &lhs for the MEM_REF expression. */
- tree lhs_addr = build_fold_addr_expr (gimple_assign_lhs (stmt));
-
- if (! is_gimple_min_invariant (lhs_addr))
- return;
-
- /* The number of bytes for the new constructor. */
- poly_int64 ref_bytes = exact_div (ref->size, BITS_PER_UNIT);
- poly_int64 count = ref_bytes - head_trim - tail_trim;
-
- /* And the new type for the CONSTRUCTOR. Essentially it's just
- a char array large enough to cover the non-trimmed parts of
- the original CONSTRUCTOR. Note we want explicit bounds here
- so that we know how many bytes to clear when expanding the
- CONSTRUCTOR. */
- tree type = build_array_type_nelts (char_type_node, count);
-
- /* Build a suitable alias type rather than using alias set zero
- to avoid pessimizing. */
- tree alias_type = reference_alias_ptr_type (gimple_assign_lhs (stmt));
-
- /* Build a MEM_REF representing the whole accessed area, starting
- at the first byte not trimmed. */
- tree exp = fold_build2 (MEM_REF, type, lhs_addr,
- build_int_cst (alias_type, head_trim));
-
- /* Now update STMT with a new RHS and LHS. */
- gimple_assign_set_lhs (stmt, exp);
- gimple_assign_set_rhs1 (stmt, build_constructor (type, NULL));
- }
-}
-
-/* STMT is a memcpy, memmove or memset. Decrement the number of bytes
- copied/set by DECREMENT. */
-static void
-decrement_count (gimple *stmt, int decrement)
-{
- tree *countp = gimple_call_arg_ptr (stmt, 2);
- gcc_assert (TREE_CODE (*countp) == INTEGER_CST);
- *countp = wide_int_to_tree (TREE_TYPE (*countp), (TREE_INT_CST_LOW (*countp)
- - decrement));
-
-}
-
-static void
-increment_start_addr (gimple *stmt, tree *where, int increment)
-{
- if (TREE_CODE (*where) == SSA_NAME)
- {
- tree tem = make_ssa_name (TREE_TYPE (*where));
- gassign *newop
- = gimple_build_assign (tem, POINTER_PLUS_EXPR, *where,
- build_int_cst (sizetype, increment));
- gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
- gsi_insert_before (&gsi, newop, GSI_SAME_STMT);
- *where = tem;
- update_stmt (gsi_stmt (gsi));
- return;
- }
-
- *where = build_fold_addr_expr (fold_build2 (MEM_REF, char_type_node,
- *where,
- build_int_cst (ptr_type_node,
- increment)));
-}
-
-/* STMT is builtin call that writes bytes in bitmap ORIG, some bytes are dead
- (ORIG & ~NEW) and need not be stored. Try to rewrite STMT to reduce
- the amount of data it actually writes.
-
- Right now we only support trimming from the head or the tail of the
- memory region. In theory we could split the mem* call, but it's
- likely of marginal value. */
-
-static void
-maybe_trim_memstar_call (ao_ref *ref, sbitmap live, gimple *stmt)
-{
- switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
- {
- case BUILT_IN_MEMCPY:
- case BUILT_IN_MEMMOVE:
- case BUILT_IN_STRNCPY:
- case BUILT_IN_MEMCPY_CHK:
- case BUILT_IN_MEMMOVE_CHK:
- case BUILT_IN_STRNCPY_CHK:
- {
- int head_trim, tail_trim;
- compute_trims (ref, live, &head_trim, &tail_trim, stmt);
-
- /* Tail trimming is easy, we can just reduce the count. */
- if (tail_trim)
- decrement_count (stmt, tail_trim);
-
- /* Head trimming requires adjusting all the arguments. */
- if (head_trim)
- {
- tree *dst = gimple_call_arg_ptr (stmt, 0);
- increment_start_addr (stmt, dst, head_trim);
- tree *src = gimple_call_arg_ptr (stmt, 1);
- increment_start_addr (stmt, src, head_trim);
- decrement_count (stmt, head_trim);
- }
- break;
- }
-
- case BUILT_IN_MEMSET:
- case BUILT_IN_MEMSET_CHK:
- {
- int head_trim, tail_trim;
- compute_trims (ref, live, &head_trim, &tail_trim, stmt);
-
- /* Tail trimming is easy, we can just reduce the count. */
- if (tail_trim)
- decrement_count (stmt, tail_trim);
-
- /* Head trimming requires adjusting all the arguments. */
- if (head_trim)
- {
- tree *dst = gimple_call_arg_ptr (stmt, 0);
- increment_start_addr (stmt, dst, head_trim);
- decrement_count (stmt, head_trim);
- }
- break;
- }
-
- default:
- break;
- }
-}
-
-/* STMT is a memory write where one or more bytes written are dead
- stores. ORIG is the bitmap of bytes stored by STMT. LIVE is the
- bitmap of stores that are actually live.
-
- Attempt to rewrite STMT so that it writes fewer memory locations. Right
- now we only support trimming at the start or end of the memory region.
- It's not clear how much there is to be gained by trimming from the middle
- of the region. */
-
-static void
-maybe_trim_partially_dead_store (ao_ref *ref, sbitmap live, gimple *stmt)
-{
- if (is_gimple_assign (stmt)
- && TREE_CODE (gimple_assign_lhs (stmt)) != TARGET_MEM_REF)
- {
- switch (gimple_assign_rhs_code (stmt))
- {
- case CONSTRUCTOR:
- maybe_trim_constructor_store (ref, live, stmt);
- break;
- case COMPLEX_CST:
- maybe_trim_complex_store (ref, live, stmt);
- break;
- default:
- break;
- }
- }
-}
-
-/* Return TRUE if USE_REF reads bytes from LIVE where live is
- derived from REF, a write reference.
-
- While this routine may modify USE_REF, it's passed by value, not
- location. So callers do not see those modifications. */
-
-static bool
-live_bytes_read (ao_ref use_ref, ao_ref *ref, sbitmap live)
-{
- /* We have already verified that USE_REF and REF hit the same object.
- Now verify that there's actually an overlap between USE_REF and REF. */
- HOST_WIDE_INT start, size;
- if (normalize_ref (&use_ref, ref)
- && (use_ref.offset - ref->offset).is_constant (&start)
- && use_ref.size.is_constant (&size))
- {
- /* If USE_REF covers all of REF, then it will hit one or more
- live bytes. This avoids useless iteration over the bitmap
- below. */
- if (start == 0 && known_eq (size, ref->size))
- return true;
-
- /* Now check if any of the remaining bits in use_ref are set in LIVE. */
- return bitmap_bit_in_range_p (live, start / BITS_PER_UNIT,
- (start + size - 1) / BITS_PER_UNIT);
- }
- return true;
-}
-
-/* Callback for dse_classify_store calling for_each_index. Verify that
- indices are invariant in the loop with backedge PHI in basic-block DATA. */
-
-static bool
-check_name (tree, tree *idx, void *data)
-{
- basic_block phi_bb = (basic_block) data;
- if (TREE_CODE (*idx) == SSA_NAME
- && !SSA_NAME_IS_DEFAULT_DEF (*idx)
- && dominated_by_p (CDI_DOMINATORS, gimple_bb (SSA_NAME_DEF_STMT (*idx)),
- phi_bb))
- return false;
- return true;
-}
-
-/* STMT stores the value 0 into one or more memory locations
- (via memset, empty constructor, calloc call, etc).
-
- See if there is a subsequent store of the value 0 to one
- or more of the same memory location(s). If so, the subsequent
- store is redundant and can be removed.
-
- The subsequent stores could be via memset, empty constructors,
- simple MEM stores, etc. */
-
-static void
-dse_optimize_redundant_stores (gimple *stmt)
-{
- int cnt = 0;
-
- /* We could do something fairly complex and look through PHIs
- like DSE_CLASSIFY_STORE, but it doesn't seem to be worth
- the effort.
-
- Look at all the immediate uses of the VDEF (which are obviously
- dominated by STMT). See if one or more stores 0 into the same
- memory locations a STMT, if so remove the immediate use statements. */
- tree defvar = gimple_vdef (stmt);
- imm_use_iterator ui;
- gimple *use_stmt;
- FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
- {
- /* Limit stmt walking. */
- if (++cnt > param_dse_max_alias_queries_per_store)
- BREAK_FROM_IMM_USE_STMT (ui);
-
- /* If USE_STMT stores 0 into one or more of the same locations
- as STMT and STMT would kill USE_STMT, then we can just remove
- USE_STMT. */
- tree fndecl;
- if ((is_gimple_assign (use_stmt)
- && gimple_vdef (use_stmt)
- && (gimple_assign_single_p (use_stmt)
- && initializer_zerop (gimple_assign_rhs1 (use_stmt))))
- || (gimple_call_builtin_p (use_stmt, BUILT_IN_NORMAL)
- && (fndecl = gimple_call_fndecl (use_stmt)) != NULL
- && (DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET
- || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET_CHK)
- && integer_zerop (gimple_call_arg (use_stmt, 1))))
- {
- ao_ref write;
-
- if (!initialize_ao_ref_for_dse (use_stmt, &write))
- BREAK_FROM_IMM_USE_STMT (ui)
-
- if (valid_ao_ref_for_dse (&write)
- && stmt_kills_ref_p (stmt, &write))
- {
- gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt);
- if (is_gimple_assign (use_stmt))
- delete_dead_or_redundant_assignment (&gsi, "redundant",
- need_eh_cleanup);
- else if (is_gimple_call (use_stmt))
- delete_dead_or_redundant_call (&gsi, "redundant");
- else
- gcc_unreachable ();
- }
- }
- }
-}
-
-/* A helper of dse_optimize_stmt.
- Given a GIMPLE_ASSIGN in STMT that writes to REF, classify it
- according to downstream uses and defs. Sets *BY_CLOBBER_P to true
- if only clobber statements influenced the classification result.
- Returns the classification. */
-
-dse_store_status
-dse_classify_store (ao_ref *ref, gimple *stmt,
- bool byte_tracking_enabled, sbitmap live_bytes,
- bool *by_clobber_p, tree stop_at_vuse)
-{
- gimple *temp;
- int cnt = 0;
- auto_bitmap visited;
-
- if (by_clobber_p)
- *by_clobber_p = true;
-
- /* Find the first dominated statement that clobbers (part of) the
- memory stmt stores to with no intermediate statement that may use
- part of the memory stmt stores. That is, find a store that may
- prove stmt to be a dead store. */
- temp = stmt;
- do
- {
- gimple *use_stmt;
- imm_use_iterator ui;
- bool fail = false;
- tree defvar;
-
- if (gimple_code (temp) == GIMPLE_PHI)
- {
- /* If we visit this PHI by following a backedge then we have to
- make sure ref->ref only refers to SSA names that are invariant
- with respect to the loop represented by this PHI node. */
- if (dominated_by_p (CDI_DOMINATORS, gimple_bb (stmt),
- gimple_bb (temp))
- && !for_each_index (ref->ref ? &ref->ref : &ref->base,
- check_name, gimple_bb (temp)))
- return DSE_STORE_LIVE;
- defvar = PHI_RESULT (temp);
- bitmap_set_bit (visited, SSA_NAME_VERSION (defvar));
- }
- else
- defvar = gimple_vdef (temp);
-
- /* If we're instructed to stop walking at region boundary, do so. */
- if (defvar == stop_at_vuse)
- return DSE_STORE_LIVE;
-
- auto_vec<gimple *, 10> defs;
- gimple *phi_def = NULL;
- FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
- {
- /* Limit stmt walking. */
- if (++cnt > param_dse_max_alias_queries_per_store)
- {
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
-
- /* We have visited ourselves already so ignore STMT for the
- purpose of chaining. */
- if (use_stmt == stmt)
- ;
- /* In simple cases we can look through PHI nodes, but we
- have to be careful with loops and with memory references
- containing operands that are also operands of PHI nodes.
- See gcc.c-torture/execute/20051110-*.c. */
- else if (gimple_code (use_stmt) == GIMPLE_PHI)
- {
- /* If we already visited this PHI ignore it for further
- processing. */
- if (!bitmap_bit_p (visited,
- SSA_NAME_VERSION (PHI_RESULT (use_stmt))))
- {
- defs.safe_push (use_stmt);
- phi_def = use_stmt;
- }
- }
- /* If the statement is a use the store is not dead. */
- else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
- {
- /* Handle common cases where we can easily build an ao_ref
- structure for USE_STMT and in doing so we find that the
- references hit non-live bytes and thus can be ignored. */
- if (byte_tracking_enabled
- && is_gimple_assign (use_stmt))
- {
- ao_ref use_ref;
- ao_ref_init (&use_ref, gimple_assign_rhs1 (use_stmt));
- if (valid_ao_ref_for_dse (&use_ref)
- && use_ref.base == ref->base
- && known_eq (use_ref.size, use_ref.max_size)
- && !live_bytes_read (use_ref, ref, live_bytes))
- {
- /* If this is a store, remember it as we possibly
- need to walk the defs uses. */
- if (gimple_vdef (use_stmt))
- defs.safe_push (use_stmt);
- continue;
- }
- }
-
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
- /* If this is a store, remember it as we possibly need to walk the
- defs uses. */
- else if (gimple_vdef (use_stmt))
- defs.safe_push (use_stmt);
- }
-
- if (fail)
- {
- /* STMT might be partially dead and we may be able to reduce
- how many memory locations it stores into. */
- if (byte_tracking_enabled && !gimple_clobber_p (stmt))
- return DSE_STORE_MAYBE_PARTIAL_DEAD;
- return DSE_STORE_LIVE;
- }
-
- /* If we didn't find any definition this means the store is dead
- if it isn't a store to global reachable memory. In this case
- just pretend the stmt makes itself dead. Otherwise fail. */
- if (defs.is_empty ())
- {
- if (ref_may_alias_global_p (ref))
- return DSE_STORE_LIVE;
-
- if (by_clobber_p)
- *by_clobber_p = false;
- return DSE_STORE_DEAD;
- }
-
- /* Process defs and remove those we need not process further. */
- for (unsigned i = 0; i < defs.length ();)
- {
- gimple *def = defs[i];
- gimple *use_stmt;
- use_operand_p use_p;
- /* If the path to check starts with a kill we do not need to
- process it further.
- ??? With byte tracking we need only kill the bytes currently
- live. */
- if (stmt_kills_ref_p (def, ref))
- {
- if (by_clobber_p && !gimple_clobber_p (def))
- *by_clobber_p = false;
- defs.unordered_remove (i);
- }
- /* In addition to kills we can remove defs whose only use
- is another def in defs. That can only ever be PHIs of which
- we track a single for simplicity reasons (we fail for multiple
- PHIs anyways). We can also ignore defs that feed only into
- already visited PHIs. */
- else if (gimple_code (def) != GIMPLE_PHI
- && single_imm_use (gimple_vdef (def), &use_p, &use_stmt)
- && (use_stmt == phi_def
- || (gimple_code (use_stmt) == GIMPLE_PHI
- && bitmap_bit_p (visited,
- SSA_NAME_VERSION
- (PHI_RESULT (use_stmt))))))
- defs.unordered_remove (i);
- else
- ++i;
- }
-
- /* If all defs kill the ref we are done. */
- if (defs.is_empty ())
- return DSE_STORE_DEAD;
- /* If more than one def survives fail. */
- if (defs.length () > 1)
- {
- /* STMT might be partially dead and we may be able to reduce
- how many memory locations it stores into. */
- if (byte_tracking_enabled && !gimple_clobber_p (stmt))
- return DSE_STORE_MAYBE_PARTIAL_DEAD;
- return DSE_STORE_LIVE;
- }
- temp = defs[0];
-
- /* Track partial kills. */
- if (byte_tracking_enabled)
- {
- clear_bytes_written_by (live_bytes, temp, ref);
- if (bitmap_empty_p (live_bytes))
- {
- if (by_clobber_p && !gimple_clobber_p (temp))
- *by_clobber_p = false;
- return DSE_STORE_DEAD;
- }
- }
- }
- /* Continue walking until there are no more live bytes. */
- while (1);
-}
-
-
-class dse_dom_walker : public dom_walker
-{
-public:
- dse_dom_walker (cdi_direction direction)
- : dom_walker (direction),
- m_live_bytes (param_dse_max_object_size),
- m_byte_tracking_enabled (false) {}
-
- virtual edge before_dom_children (basic_block);
-
-private:
- auto_sbitmap m_live_bytes;
- bool m_byte_tracking_enabled;
- void dse_optimize_stmt (gimple_stmt_iterator *);
-};
-
-/* Delete a dead call at GSI, which is mem* call of some kind. */
-static void
-delete_dead_or_redundant_call (gimple_stmt_iterator *gsi, const char *type)
-{
- gimple *stmt = gsi_stmt (*gsi);
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted %s call: ", type);
- print_gimple_stmt (dump_file, stmt, 0, dump_flags);
- fprintf (dump_file, "\n");
- }
-
- tree lhs = gimple_call_lhs (stmt);
- if (lhs)
- {
- tree ptr = gimple_call_arg (stmt, 0);
- gimple *new_stmt = gimple_build_assign (lhs, ptr);
- unlink_stmt_vdef (stmt);
- if (gsi_replace (gsi, new_stmt, true))
- bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
- }
- else
- {
- /* Then we need to fix the operand of the consuming stmt. */
- unlink_stmt_vdef (stmt);
-
- /* Remove the dead store. */
- if (gsi_remove (gsi, true))
- bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
- release_defs (stmt);
- }
-}
-
-/* Delete a dead store at GSI, which is a gimple assignment. */
-
-void
-delete_dead_or_redundant_assignment (gimple_stmt_iterator *gsi, const char *type,
- bitmap need_eh_cleanup)
-{
- gimple *stmt = gsi_stmt (*gsi);
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted %s store: ", type);
- print_gimple_stmt (dump_file, stmt, 0, dump_flags);
- fprintf (dump_file, "\n");
- }
-
- /* Then we need to fix the operand of the consuming stmt. */
- unlink_stmt_vdef (stmt);
-
- /* Remove the dead store. */
- basic_block bb = gimple_bb (stmt);
- if (gsi_remove (gsi, true) && need_eh_cleanup)
- bitmap_set_bit (need_eh_cleanup, bb->index);
-
- /* And release any SSA_NAMEs set in this statement back to the
- SSA_NAME manager. */
- release_defs (stmt);
-}
-
-/* Attempt to eliminate dead stores in the statement referenced by BSI.
-
- A dead store is a store into a memory location which will later be
- overwritten by another store without any intervening loads. In this
- case the earlier store can be deleted.
-
- In our SSA + virtual operand world we use immediate uses of virtual
- operands to detect dead stores. If a store's virtual definition
- is used precisely once by a later store to the same location which
- post dominates the first store, then the first store is dead. */
-
-void
-dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator *gsi)
-{
- gimple *stmt = gsi_stmt (*gsi);
-
- /* If this statement has no virtual defs, then there is nothing
- to do. */
- if (!gimple_vdef (stmt))
- return;
-
- /* Don't return early on *this_2(D) ={v} {CLOBBER}. */
- if (gimple_has_volatile_ops (stmt)
- && (!gimple_clobber_p (stmt)
- || TREE_CODE (gimple_assign_lhs (stmt)) != MEM_REF))
- return;
-
- ao_ref ref;
- if (!initialize_ao_ref_for_dse (stmt, &ref))
- return;
-
- /* We know we have virtual definitions. We can handle assignments and
- some builtin calls. */
- if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
- {
- tree fndecl = gimple_call_fndecl (stmt);
- switch (DECL_FUNCTION_CODE (fndecl))
- {
- case BUILT_IN_MEMCPY:
- case BUILT_IN_MEMMOVE:
- case BUILT_IN_STRNCPY:
- case BUILT_IN_MEMSET:
- case BUILT_IN_MEMCPY_CHK:
- case BUILT_IN_MEMMOVE_CHK:
- case BUILT_IN_STRNCPY_CHK:
- case BUILT_IN_MEMSET_CHK:
- {
- /* Occasionally calls with an explicit length of zero
- show up in the IL. It's pointless to do analysis
- on them, they're trivially dead. */
- tree size = gimple_call_arg (stmt, 2);
- if (integer_zerop (size))
- {
- delete_dead_or_redundant_call (gsi, "dead");
- return;
- }
-
- /* If this is a memset call that initializes an object
- to zero, it may be redundant with an earlier memset
- or empty CONSTRUCTOR of a larger object. */
- if ((DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET
- || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET_CHK)
- && integer_zerop (gimple_call_arg (stmt, 1)))
- dse_optimize_redundant_stores (stmt);
-
- enum dse_store_status store_status;
- m_byte_tracking_enabled
- = setup_live_bytes_from_ref (&ref, m_live_bytes);
- store_status = dse_classify_store (&ref, stmt,
- m_byte_tracking_enabled,
- m_live_bytes);
- if (store_status == DSE_STORE_LIVE)
- return;
-
- if (store_status == DSE_STORE_MAYBE_PARTIAL_DEAD)
- {
- maybe_trim_memstar_call (&ref, m_live_bytes, stmt);
- return;
- }
-
- if (store_status == DSE_STORE_DEAD)
- delete_dead_or_redundant_call (gsi, "dead");
- return;
- }
-
- case BUILT_IN_CALLOC:
- /* We already know the arguments are integer constants. */
- dse_optimize_redundant_stores (stmt);
- return;
-
- default:
- return;
- }
- }
-
- if (is_gimple_assign (stmt))
- {
- bool by_clobber_p = false;
-
- /* Check if this statement stores zero to a memory location,
- and if there is a subsequent store of zero to the same
- memory location. If so, remove the subsequent store. */
- if (gimple_assign_single_p (stmt)
- && initializer_zerop (gimple_assign_rhs1 (stmt)))
- dse_optimize_redundant_stores (stmt);
-
- /* Self-assignments are zombies. */
- if (operand_equal_p (gimple_assign_rhs1 (stmt),
- gimple_assign_lhs (stmt), 0))
- ;
- else
- {
- m_byte_tracking_enabled
- = setup_live_bytes_from_ref (&ref, m_live_bytes);
- enum dse_store_status store_status;
- store_status = dse_classify_store (&ref, stmt,
- m_byte_tracking_enabled,
- m_live_bytes, &by_clobber_p);
- if (store_status == DSE_STORE_LIVE)
- return;
-
- if (store_status == DSE_STORE_MAYBE_PARTIAL_DEAD)
- {
- maybe_trim_partially_dead_store (&ref, m_live_bytes, stmt);
- return;
- }
- }
-
- /* Now we know that use_stmt kills the LHS of stmt. */
-
- /* But only remove *this_2(D) ={v} {CLOBBER} if killed by
- another clobber stmt. */
- if (gimple_clobber_p (stmt)
- && !by_clobber_p)
- return;
-
- delete_dead_or_redundant_assignment (gsi, "dead", need_eh_cleanup);
- }
-}
-
-edge
-dse_dom_walker::before_dom_children (basic_block bb)
-{
- gimple_stmt_iterator gsi;
-
- for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi);)
- {
- dse_optimize_stmt (&gsi);
- if (gsi_end_p (gsi))
- gsi = gsi_last_bb (bb);
- else
- gsi_prev (&gsi);
- }
- return NULL;
-}
-
-namespace {
-
-const pass_data pass_data_dse =
-{
- GIMPLE_PASS, /* type */
- "dse", /* name */
- OPTGROUP_NONE, /* optinfo_flags */
- TV_TREE_DSE, /* tv_id */
- ( PROP_cfg | PROP_ssa ), /* properties_required */
- 0, /* properties_provided */
- 0, /* properties_destroyed */
- 0, /* todo_flags_start */
- 0, /* todo_flags_finish */
-};
-
-class pass_dse : public gimple_opt_pass
-{
-public:
- pass_dse (gcc::context *ctxt)
- : gimple_opt_pass (pass_data_dse, ctxt)
- {}
-
- /* opt_pass methods: */
- opt_pass * clone () { return new pass_dse (m_ctxt); }
- virtual bool gate (function *) { return flag_tree_dse != 0; }
- virtual unsigned int execute (function *);
-
-}; // class pass_dse
-
-unsigned int
-pass_dse::execute (function *fun)
-{
- need_eh_cleanup = BITMAP_ALLOC (NULL);
-
- renumber_gimple_stmt_uids (cfun);
-
- /* We might consider making this a property of each pass so that it
- can be [re]computed on an as-needed basis. Particularly since
- this pass could be seen as an extension of DCE which needs post
- dominators. */
- calculate_dominance_info (CDI_POST_DOMINATORS);
- calculate_dominance_info (CDI_DOMINATORS);
-
- /* Dead store elimination is fundamentally a walk of the post-dominator
- tree and a backwards walk of statements within each block. */
- dse_dom_walker (CDI_POST_DOMINATORS).walk (fun->cfg->x_exit_block_ptr);
-
- /* Removal of stores may make some EH edges dead. Purge such edges from
- the CFG as needed. */
- if (!bitmap_empty_p (need_eh_cleanup))
- {
- gimple_purge_all_dead_eh_edges (need_eh_cleanup);
- cleanup_tree_cfg ();
- }
-
- BITMAP_FREE (need_eh_cleanup);
-
- /* For now, just wipe the post-dominator information. */
- free_dominance_info (CDI_POST_DOMINATORS);
- return 0;
-}
-
-} // anon namespace
-
-gimple_opt_pass *
-make_pass_dse (gcc::context *ctxt)
-{
- return new pass_dse (ctxt);
-}
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