> I'll take your word for it ;)
Thanks. Testing on PowerPC64 revealed a couple of nits:
1. SSA names with zero uses need to be excluded from the computation, because
the first SSA name in a function returning a GIMPLE type is associated with
the RESULT_DECL and is undefined, so it would propagate the undefinedness to
every SSA name collapsed with the RESULT_DECL, i.e. unduly pessimization.
2. Removing the SUBREG_PROMOTED_VAR_P flag disables the trick present in
expand_gimple_stmt_1 for the LHS of assignment statements, so you end up with
(more) SUBREGs on the LHS of moves in RTL, hence the fixlet for loop-iv.c.
I bootstrapped/regtested it on x86-64, SPARC64, Aarch64 and PowerPC64/Linux,
and compared the code generated for the tests in gcc.c-torture/compile at -O2:
very few changes for the first 3, but around 30 tests changed for PowerPC64,
all with uninitialized variables AFAICS.
Applied on the mainline.
2017-10-08 Eric Botcazou <ebotca...@adacore.com>
* tree-outof-ssa.h (ssaexpand): Add partitions_for_undefined_values.
(always_initialized_rtx_for_ssa_name_p): New predicate.
* tree-outof-ssa.c (remove_ssa_form): Initialize new field of SA.
(finish_out_of_ssa): Free new field of SA.
* tree-ssa-coalesce.h (get_undefined_value_partitions): Declare.
* tree-ssa-coalesce.c: Include tree-ssa.h.
(get_parm_default_def_partitions): Remove extern keyword.
(get_undefined_value_partitions): New function.
* expr.c (expand_expr_real_1) <expand_decl_rtl>: For a SSA_NAME, do
not set SUBREG_PROMOTED_VAR_P on the sub-register if it may contain
uninitialized bits.
* loop-iv.c (iv_get_reaching_def): Disqualify all subregs.
2017-10-08 Eric Botcazou <ebotca...@adacore.com>
* gcc.c-torture/execute/20171008-1.c: New test.
--
Eric BotcazouIndex: expr.c
===================================================================
--- expr.c (revision 253506)
+++ expr.c (working copy)
@@ -9909,24 +9909,43 @@ expand_expr_real_1 (tree exp, rtx target
&& GET_MODE (decl_rtl) != dmode)
{
machine_mode pmode;
+ bool always_initialized_rtx;
/* Get the signedness to be used for this variable. Ensure we get
the same mode we got when the variable was declared. */
if (code != SSA_NAME)
- pmode = promote_decl_mode (exp, &unsignedp);
+ {
+ pmode = promote_decl_mode (exp, &unsignedp);
+ always_initialized_rtx = true;
+ }
else if ((g = SSA_NAME_DEF_STMT (ssa_name))
&& gimple_code (g) == GIMPLE_CALL
&& !gimple_call_internal_p (g))
- pmode = promote_function_mode (type, mode, &unsignedp,
- gimple_call_fntype (g),
- 2);
+ {
+ pmode = promote_function_mode (type, mode, &unsignedp,
+ gimple_call_fntype (g), 2);
+ always_initialized_rtx
+ = always_initialized_rtx_for_ssa_name_p (ssa_name);
+ }
else
- pmode = promote_ssa_mode (ssa_name, &unsignedp);
+ {
+ pmode = promote_ssa_mode (ssa_name, &unsignedp);
+ always_initialized_rtx
+ = always_initialized_rtx_for_ssa_name_p (ssa_name);
+ }
+
gcc_assert (GET_MODE (decl_rtl) == pmode);
temp = gen_lowpart_SUBREG (mode, decl_rtl);
- SUBREG_PROMOTED_VAR_P (temp) = 1;
- SUBREG_PROMOTED_SET (temp, unsignedp);
+
+ /* We cannot assume anything about an existing extension if the
+ register may contain uninitialized bits. */
+ if (always_initialized_rtx)
+ {
+ SUBREG_PROMOTED_VAR_P (temp) = 1;
+ SUBREG_PROMOTED_SET (temp, unsignedp);
+ }
+
return temp;
}
Index: loop-iv.c
===================================================================
--- loop-iv.c (revision 253506)
+++ loop-iv.c (working copy)
@@ -353,7 +353,7 @@ iv_get_reaching_def (rtx_insn *insn, rtx
adef = DF_REF_CHAIN (use)->ref;
/* We do not handle setting only part of the register. */
- if (DF_REF_FLAGS (adef) & DF_REF_READ_WRITE)
+ if (DF_REF_FLAGS (adef) & (DF_REF_READ_WRITE | DF_REF_SUBREG))
return GRD_INVALID;
def_insn = DF_REF_INSN (adef);
Index: tree-outof-ssa.c
===================================================================
--- tree-outof-ssa.c (revision 253506)
+++ tree-outof-ssa.c (working copy)
@@ -969,6 +969,7 @@ remove_ssa_form (bool perform_ter, struc
sa->map = map;
sa->values = values;
sa->partitions_for_parm_default_defs = get_parm_default_def_partitions (map);
+ sa->partitions_for_undefined_values = get_undefined_value_partitions (map);
}
@@ -1144,6 +1145,7 @@ finish_out_of_ssa (struct ssaexpand *sa)
BITMAP_FREE (sa->values);
delete_var_map (sa->map);
BITMAP_FREE (sa->partitions_for_parm_default_defs);
+ BITMAP_FREE (sa->partitions_for_undefined_values);
memset (sa, 0, sizeof *sa);
}
Index: tree-outof-ssa.h
===================================================================
--- tree-outof-ssa.h (revision 253506)
+++ tree-outof-ssa.h (working copy)
@@ -42,6 +42,10 @@ struct ssaexpand
/* If partition I contains an SSA name that has a default def for a
parameter, bit I will be set in this bitmap. */
bitmap partitions_for_parm_default_defs;
+
+ /* If partition I contains an SSA name that has an undefined value,
+ bit I will be set in this bitmap. */
+ bitmap partitions_for_undefined_values;
};
/* This is the singleton described above. */
@@ -70,6 +74,18 @@ get_gimple_for_ssa_name (tree exp)
return NULL;
}
+/* Return whether the RTX expression representing the storage of the outof-SSA
+ partition that the SSA name EXP is a member of is always initialized. */
+static inline bool
+always_initialized_rtx_for_ssa_name_p (tree exp)
+{
+ int p = partition_find (SA.map->var_partition, SSA_NAME_VERSION (exp));
+ if (SA.map->partition_to_view)
+ p = SA.map->partition_to_view[p];
+ gcc_assert (p != NO_PARTITION);
+ return !bitmap_bit_p (SA.partitions_for_undefined_values, p);
+}
+
extern bool ssa_is_replaceable_p (gimple *stmt);
extern void finish_out_of_ssa (struct ssaexpand *sa);
extern unsigned int rewrite_out_of_ssa (struct ssaexpand *sa);
Index: tree-ssa-coalesce.c
===================================================================
--- tree-ssa-coalesce.c (revision 253506)
+++ tree-ssa-coalesce.c (working copy)
@@ -28,6 +28,7 @@ along with GCC; see the file COPYING3.
#include "memmodel.h"
#include "tm_p.h"
#include "ssa.h"
+#include "tree-ssa.h"
#include "tree-pretty-print.h"
#include "diagnostic-core.h"
#include "dumpfile.h"
@@ -1923,7 +1924,7 @@ set_parm_default_def_partition (tree var
/* Allocate and return a bitmap that has a bit set for each partition
that contains a default def for a parameter. */
-extern bitmap
+bitmap
get_parm_default_def_partitions (var_map map)
{
bitmap parm_default_def_parts = BITMAP_ALLOC (NULL);
@@ -1935,3 +1936,28 @@ get_parm_default_def_partitions (var_map
return parm_default_def_parts;
}
+
+/* Allocate and return a bitmap that has a bit set for each partition
+ that contains an undefined value. */
+
+bitmap
+get_undefined_value_partitions (var_map map)
+{
+ bitmap undefined_value_parts = BITMAP_ALLOC (NULL);
+
+ for (unsigned int i = 1; i < num_ssa_names; i++)
+ {
+ tree var = ssa_name (i);
+ if (var
+ && !virtual_operand_p (var)
+ && !has_zero_uses (var)
+ && ssa_undefined_value_p (var))
+ {
+ const int p = var_to_partition (map, var);
+ if (p != NO_PARTITION)
+ bitmap_set_bit (undefined_value_parts, p);
+ }
+ }
+
+ return undefined_value_parts;
+}
Index: tree-ssa-coalesce.h
===================================================================
--- tree-ssa-coalesce.h (revision 253506)
+++ tree-ssa-coalesce.h (working copy)
@@ -23,5 +23,6 @@ along with GCC; see the file COPYING3.
extern var_map coalesce_ssa_name (void);
extern bool gimple_can_coalesce_p (tree, tree);
extern bitmap get_parm_default_def_partitions (var_map);
+extern bitmap get_undefined_value_partitions (var_map);
#endif /* GCC_TREE_SSA_COALESCE_H */
struct S { char c1, c2, c3, c4; } __attribute__((aligned(4)));
static char bar (char **p) __attribute__((noclone, noinline));
static struct S foo (void) __attribute__((noclone, noinline));
int i;
static char
bar (char **p)
{
i = 1;
return 0;
}
static struct S
foo (void)
{
struct S ret;
char r, s, c1, c2;
char *p = &r;
s = bar (&p);
if (s)
c2 = *p;
c1 = 0;
ret.c1 = c1;
ret.c2 = c2;
return ret;
}
int main (void)
{
struct S s = foo ();
if (s.c1 != 0)
__builtin_abort ();
return 0;
}
