modulo-sched: reject loop conditions when not decrementing with one [PR 116479]

In the commit titled 'doloop: Add support for predicated vectorized loops' the
doloop_condition_get function was changed to accept loops with decrements
larger than 1.  This patch rejects such loops for modulo-sched.

gcc/ChangeLog:

	PR rtl-optimization/116479
	* modulo-sched.cc (doloop_register_get): Reject conditions with
	decrements that are not 1.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr116479.c: New test.

Author: avieira-arm

gcc/modulo-sched.cc

@@ -356,7 +356,13 @@ doloop_register_get (rtx_insn *head, rtx_insn *tail)
     reg = XEXP (condition, 0);
   else if (GET_CODE (XEXP (condition, 0)) == PLUS
 	   && REG_P (XEXP (XEXP (condition, 0), 0)))
-    reg = XEXP (XEXP (condition, 0), 0);
+    {
+      if (CONST_INT_P (XEXP (condition, 1))
+	  && INTVAL (XEXP (condition, 1)) == -1)
+	reg = XEXP (XEXP (condition, 0), 0);
+      else
+	return NULL_RTX;
+    }
   else
     gcc_unreachable ();
 

gcc/testsuite/gcc.dg/pr116479.c

@@ -0,0 +1,26 @@
+/* PR 116479 */
+/* { dg-do run { target { bitint } } } */
+/* { dg-additional-options "-O -funroll-loops -finline-stringops -fmodulo-sched --param=max-iterations-computation-cost=637924687 -std=c23" } */
+
+#if __BITINT_MAXWIDTH__ >= 13577
+_BitInt (13577) b;
+
+void
+foo (char *ret)
+{
+  __builtin_memset (&b, 4, 697);
+  *ret = 0;
+}
+#endif
+
+int
+main ()
+{
+#if __BITINT_MAXWIDTH__ >= 13577
+  char x;
+  foo (&x);
+  for (unsigned i = 0; i < sizeof (x); i++)
+    if (x != 0)
+      __builtin_abort ();
+#endif
+}