[Bug target/91522] [10 Regression] STV is slow

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91522

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So in particular

  for (ref = DF_INSN_UID_DEFS (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
    if (!HARD_REGISTER_P (DF_REF_REG (ref)))
      for (def = DF_REG_DEF_CHAIN (DF_REF_REGNO (ref));
           def;
           def = DF_REF_NEXT_REG (def))
        analyze_register_chain (candidates, ref);

looks odd since that iterates over all defs in insn_uid, then over
all defs of that register everywhere else in the function and
analyze_register_chain then iterating over the corresponding def->use
chain.  I'd say the iteration over all defs everywhere else is
not necessary and it should be simply

Index: config/i386/i386-features.c
===================================================================
--- config/i386/i386-features.c (revision 274764)
+++ config/i386/i386-features.c (working copy)
@@ -419,10 +419,7 @@ scalar_chain::add_insn (bitmap candidate
   df_ref def;
   for (ref = DF_INSN_UID_DEFS (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
     if (!HARD_REGISTER_P (DF_REF_REG (ref)))
-      for (def = DF_REG_DEF_CHAIN (DF_REF_REGNO (ref));
-          def;
-          def = DF_REF_NEXT_REG (def))
-       analyze_register_chain (candidates, def);
+      analyze_register_chain (candidates, ref);
   for (ref = DF_INSN_UID_USES (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
     if (!DF_REF_REG_MEM_P (ref))
       analyze_register_chain (candidates, ref);

which fixes the slowness.  I'm going to test that.