+++ /dev/null
-/* Dead store elimination
- Copyright (C) 2004-2017 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"
-
-/* 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.
-
- 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.
-
- 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 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. */
-
-
-/* Bitmap of blocks that have had EH statements cleaned. We should
- remove their dead edges eventually. */
-static bitmap need_eh_cleanup;
-
-/* Return value from dse_classify_store */
-enum dse_store_status
-{
- DSE_STORE_LIVE,
- DSE_STORE_MAYBE_PARTIAL_DEAD,
- DSE_STORE_DEAD
-};
-
-/* 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:
- {
- tree size = NULL_TREE;
- if (gimple_call_num_args (stmt) == 3)
- 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;
- }
- 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)
- && ref->max_size != -1
- && ref->size != 0
- && ref->max_size == ref->size
- && (ref->offset % BITS_PER_UNIT) == 0
- && (ref->size % BITS_PER_UNIT) == 0
- && (ref->size != -1));
-}
-
-/* Normalize COPY (an ao_ref) relative to REF. Essentially when we are
- done COPY will only refer bytes found within REF.
-
- We have already verified that COPY intersects at least one
- byte with REF. */
-
-static void
-normalize_ref (ao_ref *copy, ao_ref *ref)
-{
- /* 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 (copy->offset < ref->offset)
- {
- copy->size -= (ref->offset - copy->offset);
- copy->offset = ref->offset;
- }
-
- /* If COPY extends beyond REF, chop off its size appropriately. */
- if (copy->offset + copy->size > ref->offset + ref->size)
- copy->size -= (copy->offset + copy->size - (ref->offset + ref->size));
-}
-
-/* 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. */
- if (valid_ao_ref_for_dse (&write)
- && operand_equal_p (write.base, ref->base, OEP_ADDRESS_OF)
- && write.size == write.max_size
- && ((write.offset < ref->offset
- && write.offset + write.size > ref->offset)
- || (write.offset >= ref->offset
- && write.offset < ref->offset + ref->size)))
- {
- normalize_ref (&write, ref);
- bitmap_clear_range (live_bytes,
- (write.offset - ref->offset) / BITS_PER_UNIT,
- write.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)
-{
- if (valid_ao_ref_for_dse (ref)
- && (ref->size / BITS_PER_UNIT
- <= PARAM_VALUE (PARAM_DSE_MAX_OBJECT_SIZE)))
- {
- bitmap_clear (live_bytes);
- bitmap_set_range (live_bytes, 0, ref->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. */
- int last_orig = (ref->size / BITS_PER_UNIT) - 1;
- int last_live = bitmap_last_set_bit (live);
- *trim_tail = (last_orig - last_live) & ~0x1;
-
- /* 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) & ~0x1;
-
- 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 (trim_tail * 2 >= ref->size / BITS_PER_UNIT)
- {
- /* 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 (trim_head * 2 >= ref->size / BITS_PER_UNIT)
- {
- /* 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. */
- int count = (ref->size / BITS_PER_UNIT) - 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:
- {
- 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:
- {
- 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;
- }
- }
-}
-
-/* A helper of dse_optimize_stmt.
- Given a GIMPLE_ASSIGN in STMT that writes to REF, find a candidate
- statement *USE_STMT that may prove STMT to be dead.
- Return TRUE if the above conditions are met, otherwise FALSE. */
-
-static dse_store_status
-dse_classify_store (ao_ref *ref, gimple *stmt, gimple **use_stmt,
- bool byte_tracking_enabled, sbitmap live_bytes)
-{
- gimple *temp;
- unsigned cnt = 0;
-
- *use_stmt = NULL;
-
- /* 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, *defvar_def;
- imm_use_iterator ui;
- bool fail = false;
- tree defvar;
-
- /* Limit stmt walking to be linear in the number of possibly
- dead stores. */
- if (++cnt > 256)
- return DSE_STORE_LIVE;
-
- if (gimple_code (temp) == GIMPLE_PHI)
- defvar = PHI_RESULT (temp);
- else
- defvar = gimple_vdef (temp);
- defvar_def = temp;
- temp = NULL;
- FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
- {
- cnt++;
-
- /* If we ever reach our DSE candidate stmt again fail. We
- cannot handle dead stores in loops. */
- if (use_stmt == stmt)
- {
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
- /* 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 (temp
- /* Make sure we are not in a loop latch block. */
- || gimple_bb (stmt) == gimple_bb (use_stmt)
- || dominated_by_p (CDI_DOMINATORS,
- gimple_bb (stmt), gimple_bb (use_stmt))
- /* We can look through PHIs to regions post-dominating
- the DSE candidate stmt. */
- || !dominated_by_p (CDI_POST_DOMINATORS,
- gimple_bb (stmt), gimple_bb (use_stmt)))
- {
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
- /* Do not consider the PHI as use if it dominates the
- stmt defining the virtual operand we are processing,
- we have processed it already in this case. */
- if (gimple_bb (defvar_def) != gimple_bb (use_stmt)
- && !dominated_by_p (CDI_DOMINATORS,
- gimple_bb (defvar_def),
- gimple_bb (use_stmt)))
- temp = use_stmt;
- }
- /* If the statement is a use the store is not dead. */
- else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
- {
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
- /* If this is a store, remember it or bail out if we have
- multiple ones (the will be in different CFG parts then). */
- else if (gimple_vdef (use_stmt))
- {
- if (temp)
- {
- fail = true;
- BREAK_FROM_IMM_USE_STMT (ui);
- }
- temp = 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 (!temp)
- {
- if (ref_may_alias_global_p (ref))
- return DSE_STORE_LIVE;
-
- temp = stmt;
- break;
- }
-
- if (byte_tracking_enabled && temp)
- clear_bytes_written_by (live_bytes, temp, ref);
- }
- /* Continue walking until we reach a full kill as a single statement
- or there are no more live bytes. */
- while (!stmt_kills_ref_p (temp, ref)
- && !(byte_tracking_enabled && bitmap_empty_p (live_bytes)));
-
- *use_stmt = temp;
- return DSE_STORE_DEAD;
-}
-
-
-class dse_dom_walker : public dom_walker
-{
-public:
- dse_dom_walker (cdi_direction direction)
- : dom_walker (direction),
- m_live_bytes (PARAM_VALUE (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_call (gimple_stmt_iterator *gsi)
-{
- gimple *stmt = gsi_stmt (*gsi);
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted dead call: ");
- 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. */
-
-static void
-delete_dead_assignment (gimple_stmt_iterator *gsi)
-{
- gimple *stmt = gsi_stmt (*gsi);
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted dead store: ");
- 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))
- 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))
- {
- switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
- {
- case BUILT_IN_MEMCPY:
- case BUILT_IN_MEMMOVE:
- case BUILT_IN_MEMSET:
- {
- /* 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_call (gsi);
- return;
- }
-
- gimple *use_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, &use_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_call (gsi);
- return;
- }
-
- default:
- return;
- }
- }
-
- if (is_gimple_assign (stmt))
- {
- gimple *use_stmt;
-
- /* Self-assignments are zombies. */
- if (operand_equal_p (gimple_assign_rhs1 (stmt),
- gimple_assign_lhs (stmt), 0))
- use_stmt = stmt;
- 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, &use_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_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)
- && !gimple_clobber_p (use_stmt))
- return;
-
- delete_dead_assignment (gsi);
- }
-}
-
-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 ();
-
- /* 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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