[PATCH] Avoid UNSPEC_VOLATILE or volatile ASM_OPERANDS in debug insns (PR debug/83084)

[Jakub Jelinek]

Hi!

Seems at least the scheduler treats UNSPEC_VOLATILE and perhaps volatile asm
in DEBUG_INSNs as having side-effects and schedules differently depending on
that.  While we could tweak the scheduler not to do that, these will be
actually never useful in DEBUG_INSNs anyway, we don't know what it means so
we can't represent it in debug info.

So, the following patch just makes sure we don't add them into debug_insns,
instead reset those.

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

2017-11-22  Jakub Jelinek  <ja...@redhat.com>

        PR debug/83084
        * valtrack.c (propagate_for_debug_subst, propagate_for_debug): Reset
        debug insns if they would contain UNSPEC_VOLATILE or volatile asm.
        (dead_debug_insert_temp): Likewise, but also ignore even non-volatile
        asm.

        * g++.dg/opt/pr83084.C: New test.

--- gcc/valtrack.c.jj   2017-09-12 21:58:01.000000000 +0200
+++ gcc/valtrack.c      2017-11-21 18:26:10.188009398 +0100
@@ -171,10 +171,13 @@ propagate_for_debug_subst (rtx from, con
        if (REG_P (*iter) && ++cnt > 1)
          {
            rtx dval = make_debug_expr_from_rtl (old_rtx);
+           rtx to = pair->to;
+           if (volatile_insn_p (to))
+             to = gen_rtx_UNKNOWN_VAR_LOC ();
            /* Emit a debug bind insn.  */
            rtx bind
              = gen_rtx_VAR_LOCATION (GET_MODE (old_rtx),
-                                     DEBUG_EXPR_TREE_DECL (dval), pair->to,
+                                     DEBUG_EXPR_TREE_DECL (dval), to,
                                      VAR_INIT_STATUS_INITIALIZED);
            rtx_insn *bind_insn = emit_debug_insn_before (bind, pair->insn);
            df_insn_rescan (bind_insn);
@@ -217,6 +220,8 @@ propagate_for_debug (rtx_insn *insn, rtx
                                         dest, propagate_for_debug_subst, &p);
          if (loc == INSN_VAR_LOCATION_LOC (insn))
            continue;
+         if (volatile_insn_p (loc))
+           loc = gen_rtx_UNKNOWN_VAR_LOC ();
          INSN_VAR_LOCATION_LOC (insn) = loc;
          df_insn_rescan (insn);
        }
@@ -660,6 +665,12 @@ dead_debug_insert_temp (struct dead_debu
                }
              return 0;
            }
+         /* Asm in DEBUG_INSN is never useful, we can't emit debug info for
+            that.  And for volatile_insn_p, it is actually harmful
+            - DEBUG_INSNs shouldn't have any side-effects.  */
+         else if (GET_CODE (src) == ASM_OPERANDS
+                  || volatile_insn_p (src))
+           set = NULL_RTX;
        }
 
       /* ??? Should we try to extract it from a PARALLEL?  */
--- gcc/testsuite/g++.dg/opt/pr83084.C.jj       2017-11-21 18:30:22.252935128 
+0100
+++ gcc/testsuite/g++.dg/opt/pr83084.C  2017-11-21 18:29:18.000000000 +0100
@@ -0,0 +1,16 @@
+// PR debug/83084
+// { dg-do compile }
+// { dg-options "-O2 -fcompare-debug -Wno-return-type" }
+
+enum E { F };
+template <E = F> struct A {
+  bool foo ();
+  int b;
+};
+template <> bool A<>::foo () {
+  int a;
+  do
+    if (a)
+      return false;
+  while (__atomic_compare_exchange_n (&b, &a, 0, 1, 4, 0));
+}

        Jakub