Simple Load/Store optimization

[r3896]

ir/opt/ldstopt.c

+/*
+ * Project:     libFIRM
+ * File name:   ir/opt/ldstopt.c
+ * Purpose:     load store optimizations
+ * Author:
+ * Created:
+ * CVS-ID:      $Id$
+ * Copyright:   (c) 1998-2004 Universitt Karlsruhe
+ * Licence:     This file protected by GPL -  GNU GENERAL PUBLIC LICENSE.
+ */
+# include "irnode_t.h"
+# include "irgraph_t.h"
+# include "irmode_t.h"
+# include "iropt_t.h"
+# include "ircons_t.h"
+# include "irgmod.h"
+# include "irgwalk.h"
+# include "irvrfy.h"
+# include "tv_t.h"
+# include "dbginfo_t.h"
+# include "iropt_dbg.h"
+# include "irflag_t.h"
+# include "firmstat.h"
+
+#undef IMAX
+#define IMAX(a,b)	((a) > (b) ? (a) : (b))
+
+#define MAX_PROJ	IMAX(pn_Load_max, pn_Store_max)
+
+/**
+ * walker environment
+ */
+typedef struct _walk_env_t {
+  struct obstack obst;		/**< list of all stores */
+  int changes;
+} walk_env_t;
+
+/**
+ * a Load/Store info
+ */
+typedef struct _ldst_info_t {
+  ir_node *projs[MAX_PROJ];	/**< list of Proj's of this node */
+} ldst_info_t;
+
+/**
+ * walker, clears all links first
+ */
+static void init_links(ir_node *n, void *env)
+{
+  set_irn_link(n, NULL);
+}
+
+/**
+ * get the Load/Store info of a node
+ */
+static ldst_info_t *get_info(ir_node *node, walk_env_t *env)
+{
+  ldst_info_t *info = get_irn_link(node);
+
+  if (! info) {
+    info = obstack_alloc(&env->obst, sizeof(*info));
+
+    memset(info, 0, sizeof(*info));
+
+    set_irn_link(node, info);
+  }
+  return info;
+}
+
+/**
+ * update the info for a Load/Store
+ */
+static void update_projs(ldst_info_t *info, ir_node *proj)
+{
+  long nr = get_Proj_proj(proj);
+
+  assert(0 <= nr && nr <= MAX_PROJ && "Wrong proj from LoadStore");
+
+  if (info->projs[nr]) {
+    /* there is already one, do CSE */
+    exchange(proj, info->projs[nr]);
+  }
+  else
+    info->projs[nr] = proj;
+}
+
+/**
+ * walker, collects all Load/Store/Proj nodes
+ */
+static void collect_nodes(ir_node *n, void *env)
+{
+  ir_node     *pred;
+  ldst_info_t *info;
+  walk_env_t  *wenv = env;
+
+  if (get_irn_op(n) == op_Proj) {
+    pred = get_Proj_pred(n);
+
+    if (get_irn_op(pred) == op_Load || get_irn_op(pred) == op_Store) {
+      info = get_info(pred, wenv);
+
+      update_projs(info, n);
+    }
+  }
+}
+
+/**
+ * optimize a Load
+ */
+static int optimize_load(ir_node *load)
+{
+  ldst_info_t *info = get_irn_link(load);
+  ir_mode *load_mode = get_Load_mode(load);
+  ir_node *pred, *mem, *ptr;
+  int res = 1;
+
+  if (get_Load_volatility(load) == volatility_is_volatile)
+    return 0;
+
+  /*
+   * BEWARE: one might think that checking the modes is useless, because
+   * if the pointers are identical, they refer to the same object.
+   * This is only true in strong typed languages, not is C were the following
+   * is possible a = *(type1 *)p; b = *(type2 *)p ...
+   */
+
+  ptr  = get_Load_ptr(load);
+  mem  = get_Load_mem(load);
+  pred = skip_Proj(mem);
+
+  if (! info->projs[pn_Load_res] && ! info->projs[pn_Load_X_except]) {
+    /* a Load which value is neither used nor exception checked, remove it */
+    exchange(info->projs[pn_Load_M], mem);
+    res = 1;
+  }
+  else if (get_irn_op(pred) == op_Store && get_Store_ptr(pred) == ptr &&
+	   get_irn_mode(get_Store_value(pred)) == load_mode) {
+    /*
+     * a load immediately after a store -- a read after write.
+     * We may remove the Load, if it does not have an exception handler
+     * OR they are in the same block. In the latter case the Load cannot
+     * throw an exception when the previous Store was quiet.
+     */
+    if (! info->projs[pn_Load_X_except] || get_nodes_block(load) == get_nodes_block(pred)) {
+      exchange( info->projs[pn_Load_res], get_Store_value(pred) );
+      exchange( info->projs[pn_Load_M], mem );
+
+      /* no exception */
+      if (info->projs[pn_Load_X_except])
+	exchange( info->projs[pn_Load_X_except], new_Bad());
+      res = 1;
+    }
+  }
+  else if (get_irn_op(pred) == op_Load && get_Load_ptr(pred) == ptr &&
+	   get_Load_mode(pred) == load_mode) {
+    /*
+     * a load immediately after a load -- a read after read.
+     * We may remove the second Load, if it does not have an exception handler
+     * OR they are in the same block. In the latter case the Load cannot
+     * throw an exception when the previous Load was quiet.
+     */
+    if (! info->projs[pn_Load_X_except] || get_nodes_block(load) == get_nodes_block(pred)) {
+      ldst_info_t *pred_info = get_irn_link(pred);
+
+      if (pred_info->projs[pn_Load_res]) {
+	/* we need a data proj from the previous load for this optimization */
+	exchange( info->projs[pn_Load_res], pred_info->projs[pn_Load_res] );
+	exchange( info->projs[pn_Load_M],   mem );
+      }
+      else {
+	set_Proj_pred(info->projs[pn_Load_res], pred);
+	set_nodes_block(info->projs[pn_Load_res], get_nodes_block(pred));
+	exchange( info->projs[pn_Load_M],   mem );
+      }
+
+      /* no exception */
+      if (info->projs[pn_Load_X_except])
+	exchange( info->projs[pn_Load_X_except], new_Bad());
+
+      res = 1;
+    }
+  }
+  return res;
+}
+
+/**
+ * optimize a Store
+ */
+static int optimize_store(ir_node *store)
+{
+  ldst_info_t *info = get_irn_link(store);
+  ir_node *pred, *mem, *ptr, *value, *block;
+  ir_mode *mode;
+  ldst_info_t *pred_info;
+  int res = 0;
+
+  if (get_Store_volatility(store) == volatility_is_volatile)
+    return 0;
+
+  /*
+   * BEWARE: one might think that checking the modes is useless, because
+   * if the pointers are identical, they refer to the same object.
+   * This is only true in strong typed languages, not is C were the following
+   * is possible *(type1 *)p = a; *(type2 *)p = b ...
+   */
+
+  block = get_nodes_block(store);
+  ptr   = get_Store_ptr(store);
+  mem   = get_Store_mem(store);
+  value = get_Store_value(store);
+  pred  = skip_Proj(mem);
+  mode  = get_irn_mode(value);
+
+  pred_info = get_irn_link(pred);
+
+  if (get_irn_op(pred) == op_Store && get_Store_ptr(pred) == ptr &&
+      get_nodes_block(pred) == block && get_irn_mode(get_Store_value(pred)) == mode) {
+    /*
+     * a store immediately after a store in the same block -- a write after write.
+     * We may remove the first Store, if it does not have an exception handler.
+     *
+     * TODO: What, if both have the same exception handler ???
+     */
+    if (get_Store_volatility(pred) != volatility_is_volatile && !pred_info->projs[pn_Store_X_except]) {
+      exchange( pred_info->projs[pn_Store_M], get_Store_mem(pred) );
+      res = 1;
+    }
+  }
+  else if (get_irn_op(pred) == op_Load && get_Load_ptr(pred) == ptr &&
+	   value == pred_info->projs[pn_Load_res]) {
+    /*
+     * a store a value immediately after a load -- a write after read.
+     * We may remove the second Store, if it does not have an exception handler.
+     */
+    if (! info->projs[pn_Store_X_except]) {
+      exchange( info->projs[pn_Store_M], mem );
+      res = 1;
+    }
+  }
+  return res;
+}
+
+/**
+ * walker, collects all Load/Store/Proj nodes
+ */
+static void do_load_store_optimize(ir_node *n, void *env)
+{
+  walk_env_t *wenv = env;
+
+  switch (get_irn_opcode(n)) {
+
+  case iro_Load:
+    wenv->changes |= optimize_load(n);
+    break;
+
+  case iro_Store:
+    wenv->changes |= optimize_store(n);
+    break;
+
+  default:
+    ;
+  }
+}
+
+/*
+ * do the load store optimization
+ */
+void optimize_load_store(ir_graph *irg)
+{
+  walk_env_t env;
+
+  assert(get_irg_phase_state(irg) != phase_building);
+
+  if (!get_opt_redundant_LoadStore())
+    return;
+
+  obstack_init(&env.obst);
+  env.changes = 0;
+
+  /* init the links, then collect Loads/Stores/Proj's in lists */
+  irg_walk_graph(irg, init_links, collect_nodes, &env);
+
+  /* now we have collected enough information, optimize */
+  irg_walk_graph(irg, NULL, do_load_store_optimize, &env);
+
+  obstack_free(&env.obst, NULL);
+
+  /* Handle graph state */
+  if (env.changes) {
+    if (get_irg_outs_state(current_ir_graph) == outs_consistent)
+      set_irg_outs_inconsistent(current_ir_graph);
+
+    /* is this really needed: Yes, as exception block may get bad but this might be tested */
+    if (get_irg_dom_state(current_ir_graph) == dom_consistent)
+      set_irg_dom_inconsistent(current_ir_graph);
+  }
+}

ir/opt/ldstopt.h

+/*
+ * Project:     libFIRM
+ * File name:   ir/opt/ldstopt.h
+ * Purpose:     load/store optimizations
+ * Author:      Michael Beck
+ * Created:
+ * CVS-ID:      $Id$
+ * Copyright:   (c) 1998-2004 Universitt Karlsruhe
+ * Licence:     This file protected by GPL -  GNU GENERAL PUBLIC LICENSE.
+ */
+
+/**
+ * @file ldstopt.h
+ *
+ * Load/Store optimization.
+ *
+ * @author Michael Beck
+ */
+#ifndef _LDSTOPT_H_
+#define _LDSTOPT_H_
+
+#include "irgraph.h"
+
+/** Load/Store optimization.
+ *
+ * Removes redundand non-volatile Loads and Stores.
+ * May introduce Bad nodes if exceptional control flow
+ * is removed.
+ */
+void optimize_load_store(ir_graph *irg);
+
+#endif /* _LDSTOPT_H_ */