On Thu, 16 Oct 2014, Jeff Law wrote:
BTW, I dislike having multiple DCE implementations...
Similarly. The proposal above was just to determine if we should schedule
DCE or not.
Thinking about it some more, I don't think we should need any kind of DCE
here. The rewriting in update_ssa already does a form of forward
propagation that avoids generating dead assignments, the problem only
occurs if we explicitly introduce this new assignment. So I believe we
should go back to an earlier version, like the attached, which is less
work for the compiler.
And now I can go re-read the old discussion (apparently I should avoid
gsi_replace, and there may be other ways to handle the coalescing).
--
Marc Glisse
Index: testsuite/gcc.dg/tree-ssa/pr60770-1.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/pr60770-1.c (revision 0)
+++ testsuite/gcc.dg/tree-ssa/pr60770-1.c (working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O -Wall" } */
+
+int f(int n){
+ int*p;
+ {
+ int yyy=n;
+ p=&yyy;
+ }
+ return *p; /* { dg-warning "yyy" } */
+}
Index: tree-into-ssa.c
===================================================================
--- tree-into-ssa.c (revision 216384)
+++ tree-into-ssa.c (working copy)
@@ -1837,26 +1837,35 @@ maybe_register_def (def_operand_p def_p,
{
tree def = DEF_FROM_PTR (def_p);
tree sym = DECL_P (def) ? def : SSA_NAME_VAR (def);
/* If DEF is a naked symbol that needs renaming, create a new
name for it. */
if (marked_for_renaming (sym))
{
if (DECL_P (def))
{
- tree tracked_var;
-
- def = make_ssa_name (def, stmt);
+ if (gimple_clobber_p (stmt) && is_gimple_reg (sym))
+ {
+ /* Replace clobber stmts with a default def. This new use of a
+ default definition may make it look like SSA_NAMEs have
+ conflicting lifetimes, so we need special code to let them
+ coalesce properly. */
+ unlink_stmt_vdef (stmt);
+ gsi_replace (&gsi, gimple_build_nop (), true);
+ def = get_or_create_ssa_default_def (cfun, sym);
+ }
+ else
+ def = make_ssa_name (def, stmt);
SET_DEF (def_p, def);
- tracked_var = target_for_debug_bind (sym);
+ tree tracked_var = target_for_debug_bind (sym);
if (tracked_var)
{
gimple note = gimple_build_debug_bind (tracked_var, def, stmt);
/* If stmt ends the bb, insert the debug stmt on the single
non-EH edge from the stmt. */
if (gsi_one_before_end_p (gsi) && stmt_ends_bb_p (stmt))
{
basic_block bb = gsi_bb (gsi);
edge_iterator ei;
edge e, ef = NULL;
Index: tree-ssa-live.c
===================================================================
--- tree-ssa-live.c (revision 216384)
+++ tree-ssa-live.c (working copy)
@@ -40,20 +40,21 @@ along with GCC; see the file COPYING3.
#include "stringpool.h"
#include "tree-ssanames.h"
#include "expr.h"
#include "tree-dfa.h"
#include "timevar.h"
#include "dumpfile.h"
#include "tree-ssa-live.h"
#include "diagnostic-core.h"
#include "debug.h"
#include "flags.h"
+#include "tree-ssa.h"
#ifdef ENABLE_CHECKING
static void verify_live_on_entry (tree_live_info_p);
#endif
/* VARMAP maintains a mapping from SSA version number to real variables.
All SSA_NAMES are divided into partitions. Initially each ssa_name is the
only member of it's own partition. Coalescing will attempt to group any
@@ -1086,20 +1087,24 @@ set_var_live_on_entry (tree ssa_name, tr
if (stmt)
{
def_bb = gimple_bb (stmt);
/* Mark defs in liveout bitmap temporarily. */
if (def_bb)
bitmap_set_bit (&live->liveout[def_bb->index], p);
}
else
def_bb = ENTRY_BLOCK_PTR_FOR_FN (cfun);
+ /* An undefined local variable does not need to be very alive. */
+ if (ssa_undefined_value_p (ssa_name, false))
+ return;
+
/* Visit each use of SSA_NAME and if it isn't in the same block as the def,
add it to the list of live on entry blocks. */
FOR_EACH_IMM_USE_FAST (use, imm_iter, ssa_name)
{
gimple use_stmt = USE_STMT (use);
basic_block add_block = NULL;
if (gimple_code (use_stmt) == GIMPLE_PHI)
{
/* Uses in PHI's are considered to be live at exit of the SRC block
@@ -1422,20 +1427,25 @@ verify_live_on_entry (tree_live_info_p l
fprintf (stderr, "\n");
}
else
fprintf (stderr, " and there is no default def.\n");
}
}
}
else
if (d == var)
{
+ /* An undefined local variable does not need to be very
+ alive. */
+ if (ssa_undefined_value_p (var, false))
+ continue;
+
/* The only way this var shouldn't be marked live on entry is
if it occurs in a PHI argument of the block. */
size_t z;
bool ok = false;
gimple_stmt_iterator gsi;
for (gsi = gsi_start_phis (e->dest);
!gsi_end_p (gsi) && !ok;
gsi_next (&gsi))
{
gimple phi = gsi_stmt (gsi);
Index: tree-ssa.c
===================================================================
--- tree-ssa.c (revision 216384)
+++ tree-ssa.c (working copy)
@@ -1178,24 +1178,25 @@ tree_ssa_useless_type_conversion (tree e
tree
tree_ssa_strip_useless_type_conversions (tree exp)
{
while (tree_ssa_useless_type_conversion (exp))
exp = TREE_OPERAND (exp, 0);
return exp;
}
-/* Return true if T, an SSA_NAME, has an undefined value. */
+/* Return true if T, an SSA_NAME, has an undefined value. PARTIAL is what
+ should be returned if the value is only partially undefined. */
bool
-ssa_undefined_value_p (tree t)
+ssa_undefined_value_p (tree t, bool partial)
{
gimple def_stmt;
tree var = SSA_NAME_VAR (t);
if (!var)
;
/* Parameters get their initial value from the function entry. */
else if (TREE_CODE (var) == PARM_DECL)
return false;
/* When returning by reference the return address is actually a hidden
@@ -1205,21 +1206,21 @@ ssa_undefined_value_p (tree t)
/* Hard register variables get their initial value from the ether. */
else if (TREE_CODE (var) == VAR_DECL && DECL_HARD_REGISTER (var))
return false;
/* The value is undefined iff its definition statement is empty. */
def_stmt = SSA_NAME_DEF_STMT (t);
if (gimple_nop_p (def_stmt))
return true;
/* Check if the complex was not only partially defined. */
- if (is_gimple_assign (def_stmt)
+ if (partial && is_gimple_assign (def_stmt)
&& gimple_assign_rhs_code (def_stmt) == COMPLEX_EXPR)
{
tree rhs1, rhs2;
rhs1 = gimple_assign_rhs1 (def_stmt);
rhs2 = gimple_assign_rhs2 (def_stmt);
return (TREE_CODE (rhs1) == SSA_NAME && ssa_undefined_value_p (rhs1))
|| (TREE_CODE (rhs2) == SSA_NAME && ssa_undefined_value_p (rhs2));
}
return false;
@@ -1551,32 +1552,20 @@ execute_update_addresses_taken (void)
rhs = gimple_assign_rhs1 (stmt);
if (gimple_assign_lhs (stmt) != lhs
&& !useless_type_conversion_p (TREE_TYPE (lhs),
TREE_TYPE (rhs)))
rhs = fold_build1 (VIEW_CONVERT_EXPR,
TREE_TYPE (lhs), rhs);
if (gimple_assign_lhs (stmt) != lhs)
gimple_assign_set_lhs (stmt, lhs);
- /* For var ={v} {CLOBBER}; where var lost
- TREE_ADDRESSABLE just remove the stmt. */
- if (DECL_P (lhs)
- && TREE_CLOBBER_P (rhs)
- && bitmap_bit_p (suitable_for_renaming, DECL_UID (lhs)))
- {
- unlink_stmt_vdef (stmt);
- gsi_remove (&gsi, true);
- release_defs (stmt);
- continue;
- }
-
if (gimple_assign_rhs1 (stmt) != rhs)
{
gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
gimple_assign_set_rhs_from_tree (&gsi, rhs);
}
}
else if (gimple_code (stmt) == GIMPLE_CALL)
{
unsigned i;
Index: tree-ssa.h
===================================================================
--- tree-ssa.h (revision 216384)
+++ tree-ssa.h (working copy)
@@ -44,21 +44,21 @@ extern tree target_for_debug_bind (tree)
extern void insert_debug_temp_for_var_def (gimple_stmt_iterator *, tree);
extern void insert_debug_temps_for_defs (gimple_stmt_iterator *);
extern void reset_debug_uses (gimple);
extern void release_defs_bitset (bitmap toremove);
extern void verify_ssa (bool, bool);
extern void init_tree_ssa (struct function *);
extern void delete_tree_ssa (void);
extern bool tree_ssa_useless_type_conversion (tree);
extern tree tree_ssa_strip_useless_type_conversions (tree);
-extern bool ssa_undefined_value_p (tree);
+extern bool ssa_undefined_value_p (tree, bool = true);
extern void execute_update_addresses_taken (void);
/* Given an edge_var_map V, return the PHI arg definition. */
static inline tree
redirect_edge_var_map_def (edge_var_map *v)
{
return v->def;
}
