[PATCH] loop-invariant: Split preheader edge if the preheader bb ends with jump [PR106751]

[Jakub Jelinek via Gcc-patches]

Hi!

The RTL loop passes only request simple preheaders, but don't require
fallthru preheaders, while move_invariant_reg apparently assumes the
latter, that it can just append instruction(s) to the end of the preheader
basic block.

The following patch fixes that by splitting the preheader edge if
the preheader bb ends with a JUMP_INSN (asm goto in this case).
Without that we get control flow in the middle of a bb.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-12-16  Jakub Jelinek  <ja...@redhat.com>

        PR rtl-optimization/106751
        * loop-invariant.cc (move_invariant_reg): If preheader bb ends
        with a JUMP_INSN, split the preheader edge and emit invariants
        into the new preheader basic block.

        * gcc.c-torture/compile/pr106751.c: New test.

--- gcc/loop-invariant.cc.jj    2022-01-18 11:58:59.683980614 +0100
+++ gcc/loop-invariant.cc       2022-12-15 17:14:32.906883258 +0100
@@ -1837,6 +1837,8 @@ move_invariant_reg (class loop *loop, un
       else if (dump_file)
        fprintf (dump_file, "Invariant %d moved without introducing a new "
                            "temporary register\n", invno);
+      if (JUMP_P (BB_END (preheader)))
+       preheader = split_edge (loop_preheader_edge (loop));
       reorder_insns (inv->insn, inv->insn, BB_END (preheader));
       df_recompute_luids (preheader);
 
--- gcc/testsuite/gcc.c-torture/compile/pr106751.c.jj   2022-12-15 
17:44:35.602519711 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr106751.c      2022-12-15 
17:44:21.789721827 +0100
@@ -0,0 +1,17 @@
+/* PR rtl-optimization/106751 */
+
+int *foo (void);
+
+void
+bar (void)
+{
+  asm goto ("" : : : : lab);
+  __builtin_unreachable ();
+lab:
+  while (1)
+    {
+      int o;
+      asm ("" : "=r" (o) : "g" (1));
+      *foo () = o;
+    }
+}

        Jakub