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877 lines
26 KiB
C
877 lines
26 KiB
C
/* Dead store elimination
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Copyright (C) 2004-2017 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "backend.h"
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#include "rtl.h"
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#include "tree.h"
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#include "gimple.h"
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#include "tree-pass.h"
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#include "ssa.h"
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#include "gimple-pretty-print.h"
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#include "fold-const.h"
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#include "gimple-iterator.h"
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#include "tree-cfg.h"
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#include "tree-dfa.h"
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#include "domwalk.h"
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#include "tree-cfgcleanup.h"
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#include "params.h"
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#include "alias.h"
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/* This file implements dead store elimination.
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A dead store is a store into a memory location which will later be
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overwritten by another store without any intervening loads. In this
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case the earlier store can be deleted.
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In our SSA + virtual operand world we use immediate uses of virtual
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operands to detect dead stores. If a store's virtual definition
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is used precisely once by a later store to the same location which
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post dominates the first store, then the first store is dead.
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The single use of the store's virtual definition ensures that
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there are no intervening aliased loads and the requirement that
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the second load post dominate the first ensures that if the earlier
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store executes, then the later stores will execute before the function
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exits.
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It may help to think of this as first moving the earlier store to
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the point immediately before the later store. Again, the single
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use of the virtual definition and the post-dominance relationship
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ensure that such movement would be safe. Clearly if there are
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back to back stores, then the second is redundant.
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Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
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may also help in understanding this code since it discusses the
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relationship between dead store and redundant load elimination. In
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fact, they are the same transformation applied to different views of
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the CFG. */
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/* Bitmap of blocks that have had EH statements cleaned. We should
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remove their dead edges eventually. */
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static bitmap need_eh_cleanup;
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/* Return value from dse_classify_store */
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enum dse_store_status
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{
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DSE_STORE_LIVE,
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DSE_STORE_MAYBE_PARTIAL_DEAD,
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DSE_STORE_DEAD
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};
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/* STMT is a statement that may write into memory. Analyze it and
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initialize WRITE to describe how STMT affects memory.
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Return TRUE if the the statement was analyzed, FALSE otherwise.
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It is always safe to return FALSE. But typically better optimziation
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can be achieved by analyzing more statements. */
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static bool
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initialize_ao_ref_for_dse (gimple *stmt, ao_ref *write)
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{
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/* It's advantageous to handle certain mem* functions. */
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if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
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{
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switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
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{
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case BUILT_IN_MEMCPY:
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case BUILT_IN_MEMMOVE:
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case BUILT_IN_MEMSET:
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{
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tree size = NULL_TREE;
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if (gimple_call_num_args (stmt) == 3)
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size = gimple_call_arg (stmt, 2);
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tree ptr = gimple_call_arg (stmt, 0);
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ao_ref_init_from_ptr_and_size (write, ptr, size);
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return true;
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}
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default:
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break;
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}
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}
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else if (is_gimple_assign (stmt))
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{
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ao_ref_init (write, gimple_assign_lhs (stmt));
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return true;
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}
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return false;
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}
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/* Given REF from the the alias oracle, return TRUE if it is a valid
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memory reference for dead store elimination, false otherwise.
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In particular, the reference must have a known base, known maximum
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size, start at a byte offset and have a size that is one or more
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bytes. */
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static bool
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valid_ao_ref_for_dse (ao_ref *ref)
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{
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return (ao_ref_base (ref)
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&& ref->max_size != -1
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&& ref->size != 0
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&& ref->max_size == ref->size
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&& (ref->offset % BITS_PER_UNIT) == 0
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&& (ref->size % BITS_PER_UNIT) == 0
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&& (ref->size != -1));
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}
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/* Normalize COPY (an ao_ref) relative to REF. Essentially when we are
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done COPY will only refer bytes found within REF.
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We have already verified that COPY intersects at least one
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byte with REF. */
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static void
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normalize_ref (ao_ref *copy, ao_ref *ref)
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{
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/* If COPY starts before REF, then reset the beginning of
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COPY to match REF and decrease the size of COPY by the
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number of bytes removed from COPY. */
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if (copy->offset < ref->offset)
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{
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copy->size -= (ref->offset - copy->offset);
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copy->offset = ref->offset;
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}
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/* If COPY extends beyond REF, chop off its size appropriately. */
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if (copy->offset + copy->size > ref->offset + ref->size)
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copy->size -= (copy->offset + copy->size - (ref->offset + ref->size));
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}
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/* Clear any bytes written by STMT from the bitmap LIVE_BYTES. The base
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address written by STMT must match the one found in REF, which must
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have its base address previously initialized.
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This routine must be conservative. If we don't know the offset or
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actual size written, assume nothing was written. */
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static void
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clear_bytes_written_by (sbitmap live_bytes, gimple *stmt, ao_ref *ref)
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{
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ao_ref write;
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if (!initialize_ao_ref_for_dse (stmt, &write))
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return;
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/* Verify we have the same base memory address, the write
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has a known size and overlaps with REF. */
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if (valid_ao_ref_for_dse (&write)
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&& operand_equal_p (write.base, ref->base, OEP_ADDRESS_OF)
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&& write.size == write.max_size
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&& ((write.offset < ref->offset
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&& write.offset + write.size > ref->offset)
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|| (write.offset >= ref->offset
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&& write.offset < ref->offset + ref->size)))
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{
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normalize_ref (&write, ref);
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bitmap_clear_range (live_bytes,
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(write.offset - ref->offset) / BITS_PER_UNIT,
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write.size / BITS_PER_UNIT);
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}
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}
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/* REF is a memory write. Extract relevant information from it and
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initialize the LIVE_BYTES bitmap. If successful, return TRUE.
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Otherwise return FALSE. */
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static bool
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setup_live_bytes_from_ref (ao_ref *ref, sbitmap live_bytes)
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{
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if (valid_ao_ref_for_dse (ref)
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&& (ref->size / BITS_PER_UNIT
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<= PARAM_VALUE (PARAM_DSE_MAX_OBJECT_SIZE)))
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{
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bitmap_clear (live_bytes);
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bitmap_set_range (live_bytes, 0, ref->size / BITS_PER_UNIT);
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return true;
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}
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return false;
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}
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/* Compute the number of elements that we can trim from the head and
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tail of ORIG resulting in a bitmap that is a superset of LIVE.
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Store the number of elements trimmed from the head and tail in
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TRIM_HEAD and TRIM_TAIL.
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STMT is the statement being trimmed and is used for debugging dump
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output only. */
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static void
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compute_trims (ao_ref *ref, sbitmap live, int *trim_head, int *trim_tail,
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gimple *stmt)
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{
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/* We use sbitmaps biased such that ref->offset is bit zero and the bitmap
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extends through ref->size. So we know that in the original bitmap
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bits 0..ref->size were true. We don't actually need the bitmap, just
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the REF to compute the trims. */
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/* Now identify how much, if any of the tail we can chop off. */
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int last_orig = (ref->size / BITS_PER_UNIT) - 1;
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int last_live = bitmap_last_set_bit (live);
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*trim_tail = (last_orig - last_live) & ~0x1;
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/* Identify how much, if any of the head we can chop off. */
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int first_orig = 0;
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int first_live = bitmap_first_set_bit (live);
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*trim_head = (first_live - first_orig) & ~0x1;
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if ((*trim_head || *trim_tail)
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&& dump_file && (dump_flags & TDF_DETAILS))
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{
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fprintf (dump_file, " Trimming statement (head = %d, tail = %d): ",
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*trim_head, *trim_tail);
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print_gimple_stmt (dump_file, stmt, dump_flags, 0);
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fprintf (dump_file, "\n");
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}
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}
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/* STMT initializes an object from COMPLEX_CST where one or more of the
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bytes written may be dead stores. REF is a representation of the
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memory written. LIVE is the bitmap of stores that are actually live.
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Attempt to rewrite STMT so that only the real or imaginary part of
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the object is actually stored. */
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static void
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maybe_trim_complex_store (ao_ref *ref, sbitmap live, gimple *stmt)
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{
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int trim_head, trim_tail;
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compute_trims (ref, live, &trim_head, &trim_tail, stmt);
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/* The amount of data trimmed from the head or tail must be at
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least half the size of the object to ensure we're trimming
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the entire real or imaginary half. By writing things this
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way we avoid more O(n) bitmap operations. */
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if (trim_tail * 2 >= ref->size / BITS_PER_UNIT)
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{
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/* TREE_REALPART is live */
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tree x = TREE_REALPART (gimple_assign_rhs1 (stmt));
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tree y = gimple_assign_lhs (stmt);
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y = build1 (REALPART_EXPR, TREE_TYPE (x), y);
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gimple_assign_set_lhs (stmt, y);
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gimple_assign_set_rhs1 (stmt, x);
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}
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else if (trim_head * 2 >= ref->size / BITS_PER_UNIT)
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{
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/* TREE_IMAGPART is live */
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tree x = TREE_IMAGPART (gimple_assign_rhs1 (stmt));
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tree y = gimple_assign_lhs (stmt);
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y = build1 (IMAGPART_EXPR, TREE_TYPE (x), y);
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gimple_assign_set_lhs (stmt, y);
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gimple_assign_set_rhs1 (stmt, x);
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}
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/* Other cases indicate parts of both the real and imag subobjects
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are live. We do not try to optimize those cases. */
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}
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/* STMT initializes an object using a CONSTRUCTOR where one or more of the
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bytes written are dead stores. ORIG is the bitmap of bytes stored by
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STMT. LIVE is the bitmap of stores that are actually live.
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Attempt to rewrite STMT so that only the real or imaginary part of
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the object is actually stored.
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The most common case for getting here is a CONSTRUCTOR with no elements
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being used to zero initialize an object. We do not try to handle other
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cases as those would force us to fully cover the object with the
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CONSTRUCTOR node except for the components that are dead. */
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static void
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maybe_trim_constructor_store (ao_ref *ref, sbitmap live, gimple *stmt)
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{
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tree ctor = gimple_assign_rhs1 (stmt);
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/* This is the only case we currently handle. It actually seems to
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catch most cases of actual interest. */
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gcc_assert (CONSTRUCTOR_NELTS (ctor) == 0);
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int head_trim = 0;
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int tail_trim = 0;
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compute_trims (ref, live, &head_trim, &tail_trim, stmt);
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/* Now we want to replace the constructor initializer
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with memset (object + head_trim, 0, size - head_trim - tail_trim). */
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if (head_trim || tail_trim)
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{
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/* We want &lhs for the MEM_REF expression. */
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tree lhs_addr = build_fold_addr_expr (gimple_assign_lhs (stmt));
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if (! is_gimple_min_invariant (lhs_addr))
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return;
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/* The number of bytes for the new constructor. */
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int count = (ref->size / BITS_PER_UNIT) - head_trim - tail_trim;
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/* And the new type for the CONSTRUCTOR. Essentially it's just
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a char array large enough to cover the non-trimmed parts of
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the original CONSTRUCTOR. Note we want explicit bounds here
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so that we know how many bytes to clear when expanding the
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CONSTRUCTOR. */
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tree type = build_array_type_nelts (char_type_node, count);
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/* Build a suitable alias type rather than using alias set zero
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to avoid pessimizing. */
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tree alias_type = reference_alias_ptr_type (gimple_assign_lhs (stmt));
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/* Build a MEM_REF representing the whole accessed area, starting
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at the first byte not trimmed. */
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tree exp = fold_build2 (MEM_REF, type, lhs_addr,
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build_int_cst (alias_type, head_trim));
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/* Now update STMT with a new RHS and LHS. */
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gimple_assign_set_lhs (stmt, exp);
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gimple_assign_set_rhs1 (stmt, build_constructor (type, NULL));
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}
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}
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/* STMT is a memcpy, memmove or memset. Decrement the number of bytes
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copied/set by DECREMENT. */
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static void
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decrement_count (gimple *stmt, int decrement)
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{
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tree *countp = gimple_call_arg_ptr (stmt, 2);
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gcc_assert (TREE_CODE (*countp) == INTEGER_CST);
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*countp = wide_int_to_tree (TREE_TYPE (*countp), (TREE_INT_CST_LOW (*countp)
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- decrement));
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}
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static void
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increment_start_addr (gimple *stmt, tree *where, int increment)
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{
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if (TREE_CODE (*where) == SSA_NAME)
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{
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tree tem = make_ssa_name (TREE_TYPE (*where));
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gassign *newop
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= gimple_build_assign (tem, POINTER_PLUS_EXPR, *where,
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build_int_cst (sizetype, increment));
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gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
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gsi_insert_before (&gsi, newop, GSI_SAME_STMT);
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*where = tem;
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update_stmt (gsi_stmt (gsi));
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return;
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}
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*where = build_fold_addr_expr (fold_build2 (MEM_REF, char_type_node,
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*where,
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build_int_cst (ptr_type_node,
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increment)));
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}
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/* STMT is builtin call that writes bytes in bitmap ORIG, some bytes are dead
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(ORIG & ~NEW) and need not be stored. Try to rewrite STMT to reduce
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the amount of data it actually writes.
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Right now we only support trimming from the head or the tail of the
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memory region. In theory we could split the mem* call, but it's
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likely of marginal value. */
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static void
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maybe_trim_memstar_call (ao_ref *ref, sbitmap live, gimple *stmt)
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{
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switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
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{
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case BUILT_IN_MEMCPY:
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case BUILT_IN_MEMMOVE:
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{
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int head_trim, tail_trim;
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compute_trims (ref, live, &head_trim, &tail_trim, stmt);
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/* Tail trimming is easy, we can just reduce the count. */
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if (tail_trim)
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decrement_count (stmt, tail_trim);
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/* Head trimming requires adjusting all the arguments. */
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if (head_trim)
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{
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tree *dst = gimple_call_arg_ptr (stmt, 0);
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increment_start_addr (stmt, dst, head_trim);
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tree *src = gimple_call_arg_ptr (stmt, 1);
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increment_start_addr (stmt, src, head_trim);
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decrement_count (stmt, head_trim);
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}
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break;
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}
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case BUILT_IN_MEMSET:
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{
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int head_trim, tail_trim;
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compute_trims (ref, live, &head_trim, &tail_trim, stmt);
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/* Tail trimming is easy, we can just reduce the count. */
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if (tail_trim)
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decrement_count (stmt, tail_trim);
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/* Head trimming requires adjusting all the arguments. */
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if (head_trim)
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{
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tree *dst = gimple_call_arg_ptr (stmt, 0);
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increment_start_addr (stmt, dst, head_trim);
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decrement_count (stmt, head_trim);
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}
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break;
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}
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default:
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break;
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}
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}
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/* STMT is a memory write where one or more bytes written are dead
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stores. ORIG is the bitmap of bytes stored by STMT. LIVE is the
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bitmap of stores that are actually live.
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Attempt to rewrite STMT so that it writes fewer memory locations. Right
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now we only support trimming at the start or end of the memory region.
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It's not clear how much there is to be gained by trimming from the middle
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of the region. */
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static void
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maybe_trim_partially_dead_store (ao_ref *ref, sbitmap live, gimple *stmt)
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{
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if (is_gimple_assign (stmt)
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&& TREE_CODE (gimple_assign_lhs (stmt)) != TARGET_MEM_REF)
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{
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switch (gimple_assign_rhs_code (stmt))
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{
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case CONSTRUCTOR:
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maybe_trim_constructor_store (ref, live, stmt);
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break;
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case COMPLEX_CST:
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maybe_trim_complex_store (ref, live, stmt);
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break;
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default:
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break;
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}
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}
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}
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/* A helper of dse_optimize_stmt.
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Given a GIMPLE_ASSIGN in STMT that writes to REF, find a candidate
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statement *USE_STMT that may prove STMT to be dead.
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Return TRUE if the above conditions are met, otherwise FALSE. */
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static dse_store_status
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dse_classify_store (ao_ref *ref, gimple *stmt, gimple **use_stmt,
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bool byte_tracking_enabled, sbitmap live_bytes)
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{
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gimple *temp;
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unsigned cnt = 0;
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*use_stmt = NULL;
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/* Find the first dominated statement that clobbers (part of) the
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memory stmt stores to with no intermediate statement that may use
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part of the memory stmt stores. That is, find a store that may
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prove stmt to be a dead store. */
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temp = stmt;
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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_byte_tracking_enabled (false)
|
|
|
|
{ m_live_bytes = sbitmap_alloc (PARAM_VALUE (PARAM_DSE_MAX_OBJECT_SIZE)); }
|
|
|
|
~dse_dom_walker () { sbitmap_free (m_live_bytes); }
|
|
|
|
virtual edge before_dom_children (basic_block);
|
|
|
|
private:
|
|
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, dump_flags, 0);
|
|
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, dump_flags, 0);
|
|
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);
|
|
}
|