[gcc r16-140] modulo-sched: reject loop conditions when not decrementing with one [PR 116479]

[Andre Simoes Dias Vieira via Gcc-cvs]

https://gcc.gnu.org/g:8073fa147248aa67c11227f922d91d784659077e

commit r16-140-g8073fa147248aa67c11227f922d91d784659077e
Author: Andre Vieira <andre.simoesdiasvie...@arm.com>
Date:   Fri Apr 25 14:02:43 2025 +0100

    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.

Diff:
---
 gcc/modulo-sched.cc             |  8 +++++++-
 gcc/testsuite/gcc.dg/pr116479.c | 26 ++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/gcc/modulo-sched.cc b/gcc/modulo-sched.cc
index 08af5a929e14..002346778f44 100644
--- a/gcc/modulo-sched.cc
+++ b/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 ();
 
diff --git a/gcc/testsuite/gcc.dg/pr116479.c b/gcc/testsuite/gcc.dg/pr116479.c
new file mode 100644
index 000000000000..dbbcb9aaf575
--- /dev/null
+++ b/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
+}