[PATCH] ifcvt: Punt if not onlyjump_p for find_if_case_{1,2} [PR104814]

[Jakub Jelinek via Gcc-patches]

Hi!

find_if_case_{1,2} implicitly assumes conditional jumps and rewrites them,
so if they have extra side-effects or are say asm goto, things don't work
well, either the side-effects are lost or we could ICE.
In particular, the testcase below on s390x has there a doloop instruction
that decrements a register in addition to testing it for non-zero and
conditionally jumping based on that.

The following patch fixes that by punting for !onlyjump_p case, i.e.
if there are side-effects in the jump instruction or it isn't a plain PC
setter.

Bootstrapped/regtested on {x86_64,i686,powerpc64le,aarch64,s390x}-linux,
ok for trunk?

2022-03-13  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/104814
        * ifcvt.cc (find_if_case_1, find_if_case_2): Punt if test_bb doesn't
        end with onlyjump_p.

        * gcc.c-torture/execute/pr104814.c: New test.

--- gcc/ifcvt.cc.jj     2022-02-09 12:55:50.750773751 +0100
+++ gcc/ifcvt.cc        2022-03-11 17:30:44.248855063 +0100
@@ -5259,6 +5259,10 @@ find_if_case_1 (basic_block test_bb, edg
          && CROSSING_JUMP_P (BB_END (else_bb))))
     return FALSE;
 
+  /* Verify test_bb ends in a conditional jump with no other side-effects.  */
+  if (!BB_END (test_bb) || !onlyjump_p (BB_END (test_bb)))
+    return FALSE;
+
   /* THEN has one successor.  */
   if (!single_succ_p (then_bb))
     return FALSE;
@@ -5380,6 +5384,10 @@ find_if_case_2 (basic_block test_bb, edg
          && CROSSING_JUMP_P (BB_END (else_bb))))
     return FALSE;
 
+  /* Verify test_bb ends in a conditional jump with no other side-effects.  */
+  if (!BB_END (test_bb) || !onlyjump_p (BB_END (test_bb)))
+    return FALSE;
+
   /* ELSE has one successor.  */
   if (!single_succ_p (else_bb))
     return FALSE;
--- gcc/testsuite/gcc.c-torture/execute/pr104814.c.jj   2022-03-11 
17:36:58.753651766 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr104814.c      2022-03-11 
17:36:45.120841179 +0100
@@ -0,0 +1,30 @@
+/* PR rtl-optimization/104814 */
+
+short a = 0;
+static long b = 0;
+int c = 7;
+char d = 0;
+short *e = &a;
+long f = 0;
+
+unsigned long
+foo (unsigned long h, long j)
+{
+  return j == 0 ? h : h / j;
+}
+
+int
+main ()
+{
+  long k = f;
+  for (; c; --c)
+    {
+      for (int i = 0; i < 7; ++i)
+       ;
+      long m = foo (f, --b);
+      d = ((char) m | *e) <= 43165;
+    }
+  if (b != -7)
+    __builtin_abort ();
+  return 0;
+}

        Jakub