Hello,
we currently drop clobbers on variables whose address is not taken
anymore. However, rewrite_stmt has code to replace them with an SSA_NAME
with a default definition (an uninitialized variable), and I believe
rewrite_update_stmt should do the same. This allows us to warn sometimes
(see testcase), but during the debugging I also noticed several places
where it allowed CCP to simplify further PHIs, so this is also an
optimization.
In an earlier version of the patch, I was using
get_or_create_ssa_default_def (cfun, sym);
(I was reusing the same variable). This passed bootstrap+testsuite on all
languages except for ada. Indeed, the compiler wanted to coalesce several
SSA_NAMEs, including those new ones, in out-of-ssa, but couldn't. There
are abnormal PHIs involved. Maybe it shouldn't have insisted on coalescing
an undefined ssa_name, maybe something should have prevented us from
reaching such a situation, but creating a new variable was the simplest
workaround.
Some things could be done to improve the error message in uninit:
- getting the location of the variable,
- differenciating uninitialized from clobbered,
but that can come later.
Bootstrap+testsuite (all,obj-c++,ada,go) on x86_64-unknown-linux-gnu.
2014-06-30 Marc Glisse <marc.gli...@inria.fr>
PR tree-optimization/60770
gcc/
* tree-ssa.c (execute_update_addresses_taken): Don't drop clobbers.
* tree-into-ssa.c (maybe_register_def): Replace clobbers with a
default definition.
gcc/testsuite/
* gcc.dg/tree-ssa/pr60770-1.c: New file.
--
Marc GlisseIndex: gcc/testsuite/gcc.dg/tree-ssa/pr60770-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr60770-1.c (revision 0)
+++ gcc/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: gcc/tree-into-ssa.c
===================================================================
--- gcc/tree-into-ssa.c (revision 212109)
+++ gcc/tree-into-ssa.c (working copy)
@@ -1831,26 +1831,38 @@ 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. Create a new
+ variable so we don't later think we must coalesce, which would
+ fail with some ada abnormal PHIs. Still, we try to keep a
+ similar name so error messages make sense. */
+ unlink_stmt_vdef (stmt);
+ gsi_replace (&gsi, gimple_build_nop (), true);
+ tree id = DECL_NAME (sym);
+ const char* name = id ? IDENTIFIER_POINTER (id) : 0;
+ tree newvar = create_tmp_var (TREE_TYPE (sym), name);
+ def = get_or_create_ssa_default_def (cfun, newvar);
+ }
+ 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: gcc/tree-ssa.c
===================================================================
--- gcc/tree-ssa.c (revision 212109)
+++ gcc/tree-ssa.c (working copy)
@@ -1607,32 +1607,20 @@ 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;
