[Bug rtl-optimization/70460] [4.9/5/6 Regression] Miscompilation of glibc on i686-linux starting with r234101

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70460

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, what about:
--- gcc/ira.c.jj        2016-03-21 10:12:32.000000000 +0100
+++ gcc/ira.c   2016-03-30 18:42:46.095091159 +0200
@@ -3885,18 +3885,27 @@ indirect_jump_optimize (void)
            {
              rtx_insn *def_insn = DF_REF_INSN (def);
              rtx note = find_reg_note (def_insn, REG_LABEL_OPERAND, NULL_RTX);
+             rtx lab = NULL_RTX;

              if (note)
                {
-                 /* Substitute a LABEL_REF to the label given by the
-                    note rather than using SET_SRC of DEF_INSN.
-                    DEF_INSN might be loading the label constant from
-                    a constant pool, which isn't what we want in a
-                    direct branch.  */
-                 rtx lab = gen_rtx_LABEL_REF (Pmode, XEXP (note, 0));
-                 if (validate_replace_rtx (SET_SRC (x), lab, insn))
-                   rebuild_p = true;
+                 rtx set = single_set (def_insn);
+                 if (set
+                     && GET_CODE (SET_SRC (set)) == LABEL_REF
+                     && XEXP (SET_SRC (set), 0) == XEXP (note, 0))
+                   lab = SET_SRC (set);
+                 else
+                   {
+                     rtx eqnote = find_reg_note (def_insn, REG_EQUAL,
+                                                 NULL_RTX);
+                     if (eqnote
+                         && GET_CODE (XEXP (eqnote, 0)) == LABEL_REF
+                         && XEXP (XEXP (eqnote, 0), 0) == XEXP (note, 0))
+                       lab = XEXP (eqnote, 0);
+                   }
                }
+             if (lab && validate_replace_rtx (SET_SRC (x), lab, insn))
+               rebuild_p = true;
            }
        }
     }

then?  Not trying to subst arbitrary rtxes into insn, just LABEL_REFs, both
because it is unlikely to actually help and because one would need to verify it
doesn't contain say REGs or MEMs clobbered in between def_insn and insn.