[PR100843] store by mult pieces: punt on max_len < min_len

The testcase confuses the code that detects min and max len for the
memset, so max_len ends up less than min_len.  That shouldn't be
possible, but the testcase requires us to handle this case.

The store-by-mult-pieces algorithm actually relies on min and max
lengths, so if we find them to be inconsistent, the best we can do is
punting.


for  gcc/ChangeLog

	PR middle-end/100843
	* builtins.c (try_store_by_multiple_pieces): Fail if min_len
	is greater than max_len.

for  gcc/testsuite/ChangeLog

	PR middle-end/100843
	* gcc.dg/pr100843.c: New.

gcc/builtins.c

@@ -3963,7 +3963,8 @@ try_store_by_multiple_pieces (rtx to, rtx len, unsigned int ctz_len,
   else if (max_len == min_len)
     blksize = max_len;
   else
-    gcc_unreachable ();
+    /* Huh, max_len < min_len?  Punt.  See pr100843.c.  */
+    return false;
   if (min_len >= blksize)
     {
       min_len -= blksize;

gcc/testsuite/gcc.dg/pr100843.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -w" } */
+
+char c;
+void *memset();
+void test_integer_conversion_memset(void *d) {
+  memset(d, '\0', c);
+}