[PATCH] sched-rgn: run add_branch_dependencies for sel-sched (PR 84301)

[Alexander Monakov]

Hi,

The add_branch_dependencies function is fairly unusual in that it creates
dependence edges "out of thin air" for all sorts of instructions preceding
BB end. I think that is really unfortunate (explicit barriers in RTL would
be more natural), but I've already complained about that in the PR.

The bug/regression is that this function was not run for sel-sched, but the
testcase uncovers that moving a USE away from the return insn can break
assumptions in mode-switching code.

Solve this by running the first part of add_branch_dependencies where it
sets CANT_MOVE flags on immovable non-branch insns.

Bootstrapped/regtested on x86_64 with sel-sched active. OK to apply?

Alexander


        PR target/84301
        * sched-rgn.c (add_branch_dependences): Move sel_sched_p check here...
        (compute_block_dependences): ... from here.

        * gcc.target/i386/pr84301.c: New test.

diff --git a/gcc/sched-rgn.c b/gcc/sched-rgn.c
index 8c3a740b70e..3c67fccb9b1 100644
--- a/gcc/sched-rgn.c
+++ b/gcc/sched-rgn.c
@@ -2497,6 +2497,11 @@ add_branch_dependences (rtx_insn *head, rtx_insn *tail)
       while (insn != head && DEBUG_INSN_P (insn));
     }
 
+  /* Selective scheduling handles control dependencies by itself, and
+     CANT_MOVE flags ensure that other insns will be kept in place.  */
+  if (sel_sched_p ())
+    return;
+
   /* Make sure these insns are scheduled last in their block.  */
   insn = last;
   if (insn != 0)
@@ -2725,9 +2730,7 @@ compute_block_dependences (int bb)
 
   sched_analyze (&tmp_deps, head, tail);
 
-  /* Selective scheduling handles control dependencies by itself.  */
-  if (!sel_sched_p ())
-    add_branch_dependences (head, tail);
+  add_branch_dependences (head, tail);
 
   if (current_nr_blocks > 1)
     propagate_deps (bb, &tmp_deps);
diff --git a/gcc/testsuite/gcc.target/i386/pr84301.c 
b/gcc/testsuite/gcc.target/i386/pr84301.c
index e69de29bb2d..f1708b8ea6c 100644
--- a/gcc/testsuite/gcc.target/i386/pr84301.c
+++ b/gcc/testsuite/gcc.target/i386/pr84301.c
@@ -0,0 +1,15 @@
+/* PR target/84301 */
+/* { dg-do compile } */
+/* { dg-options "-march=bdver1 -O1 -fexpensive-optimizations -fschedule-insns 
-fselective-scheduling -fno-dce -fno-tree-dce --param max-pending-list-length=0 
--param selsched-max-lookahead=2" } */
+
+int lr;
+long int xl;
+
+int
+v4 (void)
+{
+  int mp;
+
+  ++xl;
+  mp = (lr - xl) > 1;
+}