tree-dse: Fix mem* head trimming if call has lhs [PR94130]

As the testcase shows, if DSE decides to head trim {mem{set,cpy,move},strncpy}
and the call has lhs, it is incorrect to leave the lhs as is, because it
will then point to the adjusted address (base + head_trim) instead of the
original base.
The following patch fixes that by dropping the lhs of the call and assigning
lhs the original base in a following statement.

2020-03-12  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/94130
	* tree-ssa-dse.c: Include gimplify.h.
	(increment_start_addr): If stmt has lhs, drop the lhs from call and
	set it after the call to the original value of the first argument.
	Formatting fixes.
	(decrement_count): Formatting fix.

	* gcc.c-torture/execute/pr94130.c: New test.

1 files changed, 16 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr94130.c b/gcc/testsuite/gcc.c-torture/execute/pr94130.c
new file mode 100644
index 0000000..044e578
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr94130.c
@@ -0,0 +1,16 @@
+/* PR tree-optimization/94130 */
+
+int
+main ()
+{
+  int a[8];
+  char *b = __builtin_memset (a, 0, sizeof (a));
+  a[0] = 1;
+  a[1] = 2;
+  a[2] = 3;
+  if (b != (char *) a)
+    __builtin_abort ();
+  else
+    asm volatile ("" : : "g" (a) : "memory");
+  return 0;
+}