gimple-fold: Transform stp*cpy_chk to str*cpy directly

Avoid going through another folding cycle and use the ignore flag to
directly transform BUILT_IN_STPCPY_CHK to BUILT_IN_STRCPY when set,
likewise for BUILT_IN_STPNCPY_CHK to BUILT_IN_STPNCPY.

Dump the transformation in dump_file so that we can verify in tests that
the direct transformation actually happened.

gcc/ChangeLog:

	* gimple-fold.c (dump_transformation): New function.
	(gimple_fold_builtin_stxcpy_chk,
	gimple_fold_builtin_stxncpy_chk): Use it.  Simplify to
	BUILT_IN_STRNCPY if return value is not used.

gcc/testsuite/ChangeLog:

	* gcc.dg/fold-stringops-1.c: New test.

Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/fold-stringops-1.c b/gcc/testsuite/gcc.dg/fold-stringops-1.c
new file mode 100644
index 0000000..e26632a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fold-stringops-1.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-lower-details" } */
+
+char dst[2048];
+
+char *
+copy1 (const char *src, int cond)
+{
+  __builtin___stpncpy_chk (dst, src, 42, __builtin_object_size (dst, 0));
+
+  return dst;
+}
+
+char *
+copy2 (void)
+{
+  __builtin___stpcpy_chk (dst, "Hello world", __builtin_object_size (dst, 0));
+
+  return dst;
+}
+/* { dg-final { scan-tree-dump "simplified __builtin___stpncpy_chk to __builtin_strncpy" "lower" } } */
+/* { dg-final { scan-tree-dump "simplified __builtin___stpcpy_chk to __builtin_strcpy" "lower" } } */
+