[4.7 PATCH] Optimize snprintf (buf, 5, "abcd") into memcpy (PR middle-end/47917)
Jakub Jelinek
jakub@redhat.com
Mon Feb 28 22:04:00 GMT 2011
Hi!
This patch optimizes snprintf with constant second argument
and format string without any % chars or "%s" if the second
argument is known to be greater than strlen of the string.
We could optimize also the case where it is smaller by emitting
either strcpy from a modified string (but then we risk .rodata growth),
or by doing memcpy on length - 1 followed by a single byte zero
store at the end of buffer, but then it might grow code size,
so for now I've left those cases out.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for 4.7?
2011-02-28 Jakub Jelinek <jakub@redhat.com>
PR middle-end/47917
* builtins.c (fold_builtin_snprintf): New function.
(fold_builtin_3): Call it for BUILT_IN_SNPRINTF.
(fold_builtin_4): Likewise.
* gcc.c-torture/execute/pr47917.c: New test.
* gcc.dg/pr47917.c: New test.
--- gcc/builtins.c.jj 2011-02-26 16:02:49.000000000 +0100
+++ gcc/builtins.c 2011-02-28 14:00:04.000000000 +0100
@@ -191,6 +191,7 @@ static tree fold_builtin_strncat (locati
static tree fold_builtin_strspn (location_t, tree, tree);
static tree fold_builtin_strcspn (location_t, tree, tree);
static tree fold_builtin_sprintf (location_t, tree, tree, tree, int);
+static tree fold_builtin_snprintf (location_t, tree, tree, tree, tree, int);
static rtx expand_builtin_object_size (tree);
static rtx expand_builtin_memory_chk (tree, rtx, enum machine_mode,
@@ -10600,6 +10601,9 @@ fold_builtin_3 (location_t loc, tree fnd
case BUILT_IN_SPRINTF:
return fold_builtin_sprintf (loc, arg0, arg1, arg2, ignore);
+ case BUILT_IN_SNPRINTF:
+ return fold_builtin_snprintf (loc, arg0, arg1, arg2, NULL_TREE, ignore);
+
case BUILT_IN_STRCPY_CHK:
case BUILT_IN_STPCPY_CHK:
return fold_builtin_stxcpy_chk (loc, fndecl, arg0, arg1, arg2, NULL_TREE,
@@ -10665,6 +10669,9 @@ fold_builtin_4 (location_t loc, tree fnd
case BUILT_IN_STRNCAT_CHK:
return fold_builtin_strncat_chk (loc, fndecl, arg0, arg1, arg2, arg3);
+ case BUILT_IN_SNPRINTF:
+ return fold_builtin_snprintf (loc, arg0, arg1, arg2, arg3, ignore);
+
case BUILT_IN_FPRINTF_CHK:
case BUILT_IN_VFPRINTF_CHK:
if (!validate_arg (arg1, INTEGER_TYPE)
@@ -11923,6 +11930,127 @@ fold_builtin_sprintf (location_t loc, tr
return call;
}
+/* Simplify a call to the snprintf builtin with arguments DEST, DESTSIZE,
+ FMT, and ORIG. ORIG may be null if this is a 3-argument call. We don't
+ attempt to simplify calls with more than 4 arguments.
+
+ Return NULL_TREE if no simplification was possible, otherwise return the
+ simplified form of the call as a tree. If IGNORED is true, it means that
+ the caller does not use the returned value of the function. */
+
+static tree
+fold_builtin_snprintf (location_t loc, tree dest, tree destsize, tree fmt,
+ tree orig, int ignored)
+{
+ tree call, retval;
+ const char *fmt_str = NULL;
+ unsigned HOST_WIDE_INT destlen;
+
+ /* Verify the required arguments in the original call. We deal with two
+ types of snprintf() calls: 'snprintf (str, cst, fmt)' and
+ 'snprintf (dest, cst, "%s", orig)'. */
+ if (!validate_arg (dest, POINTER_TYPE)
+ || !validate_arg (destsize, INTEGER_TYPE)
+ || !validate_arg (fmt, POINTER_TYPE))
+ return NULL_TREE;
+ if (orig && !validate_arg (orig, POINTER_TYPE))
+ return NULL_TREE;
+
+ if (!host_integerp (destsize, 1))
+ return NULL_TREE;
+
+ /* Check whether the format is a literal string constant. */
+ fmt_str = c_getstr (fmt);
+ if (fmt_str == NULL)
+ return NULL_TREE;
+
+ call = NULL_TREE;
+ retval = NULL_TREE;
+
+ if (!init_target_chars ())
+ return NULL_TREE;
+
+ destlen = tree_low_cst (destsize, 1);
+
+ /* If the format doesn't contain % args or %%, use strcpy. */
+ if (strchr (fmt_str, target_percent) == NULL)
+ {
+ tree fn = implicit_built_in_decls[BUILT_IN_STRCPY];
+ size_t len = strlen (fmt_str);
+
+ /* Don't optimize snprintf (buf, 4, "abc", ptr++). */
+ if (orig)
+ return NULL_TREE;
+
+ /* We could expand this as
+ memcpy (str, fmt, cst - 1); str[cst - 1] = '\0';
+ or to
+ memcpy (str, fmt_with_nul_at_cstm1, cst);
+ but in the former case that might increase code size
+ and in the latter case grow .rodata section too much.
+ So punt for now. */
+ if (len >= destlen)
+ return NULL_TREE;
+
+ if (!fn)
+ return NULL_TREE;
+
+ /* Convert snprintf (str, cst, fmt) into strcpy (str, fmt) when
+ 'format' is known to contain no % formats and
+ strlen (fmt) < cst. */
+ call = build_call_expr_loc (loc, fn, 2, dest, fmt);
+
+ if (!ignored)
+ retval = build_int_cst (NULL_TREE, strlen (fmt_str));
+ }
+
+ /* If the format is "%s", use strcpy if the result isn't used. */
+ else if (fmt_str && strcmp (fmt_str, target_percent_s) == 0)
+ {
+ tree fn = implicit_built_in_decls[BUILT_IN_STRCPY];
+ unsigned HOST_WIDE_INT origlen;
+
+ /* Don't crash on snprintf (str1, cst, "%s"). */
+ if (!orig)
+ return NULL_TREE;
+
+ retval = c_strlen (orig, 1);
+ if (!retval || !host_integerp (retval, 1))
+ return NULL_TREE;
+
+ origlen = tree_low_cst (retval, 1);
+ /* We could expand this as
+ memcpy (str1, str2, cst - 1); str1[cst - 1] = '\0';
+ or to
+ memcpy (str1, str2_with_nul_at_cstm1, cst);
+ but in the former case that might increase code size
+ and in the latter case grow .rodata section too much.
+ So punt for now. */
+ if (origlen >= destlen)
+ return NULL_TREE;
+
+ /* Convert snprintf (str1, cst, "%s", str2) into
+ strcpy (str1, str2) if strlen (str2) < cst. */
+ if (!fn)
+ return NULL_TREE;
+
+ call = build_call_expr_loc (loc, fn, 2, dest, orig);
+
+ if (ignored)
+ retval = NULL_TREE;
+ }
+
+ if (call && retval)
+ {
+ retval = fold_convert_loc
+ (loc, TREE_TYPE (TREE_TYPE (implicit_built_in_decls[BUILT_IN_SNPRINTF])),
+ retval);
+ return build2 (COMPOUND_EXPR, TREE_TYPE (retval), call, retval);
+ }
+ else
+ return call;
+}
+
/* Expand a call EXP to __builtin_object_size. */
rtx
--- gcc/testsuite/gcc.c-torture/execute/pr47917.c.jj 2011-02-28 14:04:39.000000000 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr47917.c 2011-02-28 14:01:05.000000000 +0100
@@ -0,0 +1,32 @@
+/* PR middle-end/47917 */
+
+extern int snprintf (char *, __SIZE_TYPE__, const char *, ...);
+extern int memcmp (const void *, const void *, __SIZE_TYPE__);
+extern void abort (void);
+
+char buf1[6], buf2[6], buf3[4], buf4[4];
+int i;
+
+int
+foo (void)
+{
+ int ret = snprintf (buf1, sizeof buf1, "abcde");
+ ret += snprintf (buf2, sizeof buf2, "abcdef") * 16;
+ ret += snprintf (buf3, sizeof buf3, "%s", i++ < 6 ? "abc" : "def") * 256;
+ ret += snprintf (buf4, sizeof buf4, "%s", i++ > 10 ? "abcde" : "defgh") * 4096;
+ return ret;
+}
+
+int
+main (void)
+{
+ if (foo () != 5 + 6 * 16 + 3 * 256 + 5 * 4096)
+ abort ();
+ if (memcmp (buf1, "abcde", 6) != 0
+ || memcmp (buf2, "abcde", 6) != 0
+ || memcmp (buf3, "abc", 4) != 0
+ || memcmp (buf4, "def", 4) != 0
+ || i != 2)
+ abort ();
+ return 0;
+}
--- gcc/testsuite/gcc.dg/pr47917.c.jj 2011-02-28 14:04:58.000000000 +0100
+++ gcc/testsuite/gcc.dg/pr47917.c 2011-02-28 14:07:22.000000000 +0100
@@ -0,0 +1,38 @@
+/* PR middle-end/47917 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+extern int snprintf (char *, __SIZE_TYPE__, const char *, ...);
+extern int memcmp (const void *, const void *, __SIZE_TYPE__);
+extern void abort (void);
+
+char buf1[6], buf2[6], buf3[4], buf4[4];
+int i;
+
+int
+foo (void)
+{
+ int ret = snprintf (buf1, sizeof buf1, "abcde");
+ ret += snprintf (buf2, sizeof buf2, "abcdef") * 16;
+ ret += snprintf (buf3, sizeof buf3, "%s", i++ < 6 ? "abc" : "def") * 256;
+ ret += snprintf (buf4, sizeof buf4, "%s", i++ > 10 ? "abcde" : "defgh") * 4096;
+ return ret;
+}
+
+int
+main (void)
+{
+ if (foo () != 5 + 6 * 16 + 3 * 256 + 5 * 4096)
+ abort ();
+ if (memcmp (buf1, "abcde", 6) != 0
+ || memcmp (buf2, "abcde", 6) != 0
+ || memcmp (buf3, "abc", 4) != 0
+ || memcmp (buf4, "def", 4) != 0
+ || i != 2)
+ abort ();
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "snprintf" 2 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "sprintf" 0 "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
Jakub
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