CbC/CbC_gcc: gcc/tree-ssa-dse.c comparison

comparison gcc/tree-ssa-dse.c @ 145:1830386684a0

gcc-9.2.0

author	anatofuz
date	Thu, 13 Feb 2020 11:34:05 +0900
parents	84e7813d76e9
children

comparison

equal deleted inserted replaced

-:84e7813d76e9
+:1830386684a0
-/* Dead store elimination
+/* Dead and redundant store elimination
-Copyright (C) 2004-2018 Free Software Foundation, Inc.
+Copyright (C) 2004-2020 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
 #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"
+#include "builtins.h"
+#include "gimple-fold.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.
+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 dead stores.  If a store's virtual definition
+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.
+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
 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.
+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;
-/* 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'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_MEMCPY:
-	  case BUILT_IN_MEMMOVE:
+	case BUILT_IN_MEMMOVE:
-	  case BUILT_IN_MEMSET:
+	case BUILT_IN_MEMSET:
-	    {
+	case BUILT_IN_MEMCPY_CHK:
-	      tree size = NULL_TREE;
+	case BUILT_IN_MEMMOVE_CHK:
-	      if (gimple_call_num_args (stmt) == 3)
+	case BUILT_IN_MEMSET_CHK:
-		size = gimple_call_arg (stmt, 2);
+	case BUILT_IN_STRNCPY:
-	      tree ptr = gimple_call_arg (stmt, 0);
+	case BUILT_IN_STRNCPY_CHK:
-	      ao_ref_init_from_ptr_and_size (write, ptr, size);
+	  {
-	      return true;
+	    tree size = gimple_call_arg (stmt, 2);
-	    }
+	    tree ptr = gimple_call_arg (stmt, 0);
-	  default:
+	    ao_ref_init_from_ptr_and_size (write, ptr, size);
-	    break;
+	    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));
 {
 HOST_WIDE_INT const_size;
 if (valid_ao_ref_for_dse (ref)
 && ref->size.is_constant (&const_size)
 && (const_size / BITS_PER_UNIT
-	  <= PARAM_VALUE (PARAM_DSE_MAX_OBJECT_SIZE)))
+	  <= param_dse_max_object_size))
 {
 bitmap_clear (live_bytes);
 bitmap_set_range (live_bytes, 0, const_size / BITS_PER_UNIT);
 return true;
 }
 likely of marginal value.  */
 static void
 maybe_trim_memstar_call (ao_ref *ref, sbitmap live, gimple *stmt)
 {
+int head_trim, tail_trim;
 switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
 {
+case BUILT_IN_STRNCPY:
+case BUILT_IN_STRNCPY_CHK:
+compute_trims (ref, live, &head_trim, &tail_trim, stmt);
+if (head_trim)
+	{
+	  /* Head trimming of strncpy is only possible if we can
+	     prove all bytes we would trim are non-zero (or we could
+	     turn the strncpy into memset if there must be zero
+	     among the head trimmed bytes).  If we don't know anything
+	     about those bytes, the presence or absence of '\0' bytes
+	     in there will affect whether it acts for the non-trimmed
+	     bytes as memset or memcpy/strncpy.  */
+	  c_strlen_data lendata = { };
+	  int orig_head_trim = head_trim;
+	  tree srcstr = gimple_call_arg (stmt, 1);
+	  if (!get_range_strlen (srcstr, &lendata, /*eltsize=*/1)
+	      || !tree_fits_uhwi_p (lendata.minlen))
+	    head_trim = 0;
+	  else if (tree_to_uhwi (lendata.minlen) < (unsigned) head_trim)
+	    {
+	      head_trim = tree_to_uhwi (lendata.minlen);
+	      if ((orig_head_trim & (UNITS_PER_WORD - 1)) == 0)
+		head_trim &= ~(UNITS_PER_WORD - 1);
+	    }
+	  if (orig_head_trim != head_trim
+	      && dump_file
+	      && (dump_flags & TDF_DETAILS))
+	    fprintf (dump_file,
+		     "  Adjusting strncpy trimming to (head = %d,"
+		     " tail = %d)\n", head_trim, tail_trim);
+	}
+goto do_memcpy;
 case BUILT_IN_MEMCPY:
 case BUILT_IN_MEMMOVE:
-{
+case BUILT_IN_MEMCPY_CHK:
-	int head_trim, tail_trim;
+case BUILT_IN_MEMMOVE_CHK:
-	compute_trims (ref, live, &head_trim, &tail_trim, stmt);
+compute_trims (ref, live, &head_trim, &tail_trim, stmt);
-	/* Tail trimming is easy, we can just reduce the count.  */
+do_memcpy:
-if (tail_trim)
+/* Tail trimming is easy, we can just reduce the count.  */
-	  decrement_count (stmt, tail_trim);
+if (tail_trim)
+	decrement_count (stmt, tail_trim);
-	/* Head trimming requires adjusting all the arguments.  */
-if (head_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);
+	  /* For __*_chk need to adjust also the last argument.  */
-	    tree *src = gimple_call_arg_ptr (stmt, 1);
+	  if (gimple_call_num_args (stmt) == 4)
-	    increment_start_addr (stmt, src, head_trim);
+	    {
-	    decrement_count (stmt, head_trim);
+	      tree size = gimple_call_arg (stmt, 3);
-	  }
+	      if (!tree_fits_uhwi_p (size))
-break;
+		break;
-}
+	      if (!integer_all_onesp (size))
+		{
+		  unsigned HOST_WIDE_INT sz = tree_to_uhwi (size);
+		  if (sz < (unsigned) head_trim)
+		    break;
+		  tree arg = wide_int_to_tree (TREE_TYPE (size),
+					       sz - head_trim);
+		  gimple_call_set_arg (stmt, 3, arg);
+		}
+	    }
+	  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);
-	compute_trims (ref, live, &head_trim, &tail_trim, stmt);
+/* Tail trimming is easy, we can just reduce the count.  */
-	/* Tail trimming is easy, we can just reduce the count.  */
+if (tail_trim)
-if (tail_trim)
+	decrement_count (stmt, tail_trim);
-	  decrement_count (stmt, tail_trim);
+/* Head trimming requires adjusting all the arguments.  */
-	/* Head trimming requires adjusting all the arguments.  */
+if (head_trim)
-if (head_trim)
+	{
-{
+	  /* For __*_chk need to adjust also the last argument.  */
-	    tree *dst = gimple_call_arg_ptr (stmt, 0);
+	  if (gimple_call_num_args (stmt) == 4)
-	    increment_start_addr (stmt, dst, head_trim);
+	    {
-	    decrement_count (stmt, head_trim);
+	      tree size = gimple_call_arg (stmt, 3);
-	  }
+	      if (!tree_fits_uhwi_p (size))
-	break;
+		break;
-}
+	      if (!integer_all_onesp (size))
+		{
-default:
+		  unsigned HOST_WIDE_INT sz = tree_to_uhwi (size);
-	break;
+		  if (sz < (unsigned) head_trim)
+		    break;
+		  tree arg = wide_int_to_tree (TREE_TYPE (size),
+					       sz - head_trim);
+		  gimple_call_set_arg (stmt, 3, arg);
+		}
+	    }
+	  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
 			 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.  */
-static dse_store_status
+dse_store_status
 dse_classify_store (ao_ref *ref, gimple *stmt,
 		    bool byte_tracking_enabled, sbitmap live_bytes,
-		    bool *by_clobber_p = NULL)
+		    bool *by_clobber_p, tree stop_at_vuse)
 {
 gimple *temp;
 int cnt = 0;
 auto_bitmap visited;
 	  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_VALUE (PARAM_DSE_MAX_ALIAS_QUERIES_PER_STORE))
+	  if (++cnt > param_dse_max_alias_queries_per_store)
 	    {
 	      fail = true;
 	      BREAK_FROM_IMM_USE_STMT (ui);
 	    }
 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_live_bytes (param_dse_max_object_size),
 m_byte_tracking_enabled (false) {}
 virtual edge before_dom_children (basic_block);
 private:
 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)
+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 dead call: ");
+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);
 }
 }
 /* Delete a dead store at GSI, which is a gimple assignment. */
-static void
+void
-delete_dead_assignment (gimple_stmt_iterator *gsi)
+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 dead store: ");
+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))
+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);
 /* 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)))
+tree fndecl = gimple_call_fndecl (stmt);
-	{
+switch (DECL_FUNCTION_CODE (fndecl))
-	  case BUILT_IN_MEMCPY:
+	{
-	  case BUILT_IN_MEMMOVE:
+	case BUILT_IN_MEMCPY:
-	  case BUILT_IN_MEMSET:
+	case BUILT_IN_MEMMOVE:
-	    {
+	case BUILT_IN_STRNCPY:
-	      /* Occasionally calls with an explicit length of zero
+	case BUILT_IN_MEMSET:
-		 show up in the IL.  It's pointless to do analysis
+	case BUILT_IN_MEMCPY_CHK:
-		 on them, they're trivially dead.  */
+	case BUILT_IN_MEMMOVE_CHK:
-	      tree size = gimple_call_arg (stmt, 2);
+	case BUILT_IN_STRNCPY_CHK:
-	      if (integer_zerop (size))
+	case BUILT_IN_MEMSET_CHK:
-		{
+	  {
-		  delete_dead_call (gsi);
+	    /* Occasionally calls with an explicit length of zero
-		  return;
+	       show up in the IL.  It's pointless to do analysis
-		}
+	       on them, they're trivially dead.  */
+	    tree size = gimple_call_arg (stmt, 2);
-	      enum dse_store_status store_status;
+	    if (integer_zerop (size))
-	      m_byte_tracking_enabled
+	      {
-		= setup_live_bytes_from_ref (&ref, m_live_bytes);
+		delete_dead_or_redundant_call (gsi, "dead");
-	      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)
-		{
+	    /* If this is a memset call that initializes an object
-		  maybe_trim_memstar_call (&ref, m_live_bytes, stmt);
+	       to zero, it may be redundant with an earlier memset
-		  return;
+	       or empty CONSTRUCTOR of a larger object.  */
-		}
+	    if ((DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET
+		 || DECL_FUNCTION_CODE (fndecl) == BUILT_IN_MEMSET_CHK)
-	      if (store_status == DSE_STORE_DEAD)
+		&& integer_zerop (gimple_call_arg (stmt, 1)))
-		delete_dead_call (gsi);
+	      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)
-	  default:
+	      {
+		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))
 	;
 	 another clobber stmt.  */
 if (gimple_clobber_p (stmt)
 	  && !by_clobber_p)
 	return;
-delete_dead_assignment (gsi);
+delete_dead_or_redundant_assignment (gsi, "dead", need_eh_cleanup);
 }
 }
 edge
 dse_dom_walker::before_dom_children (basic_block bb)
 unsigned int
 pass_dse::execute (function *fun)
 {
 need_eh_cleanup = BITMAP_ALLOC (NULL);
-renumber_gimple_stmt_uids ();
+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.  */

Mercurial > hg > CbC > CbC_gcc

comparison gcc/tree-ssa-dse.c @ 145:1830386684a0