[Bug target/17381] Unnecessary register move for float extend

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2009-01-15 19:58 -------
This is the patch which fixes the issue:Index: regrename.c
===================================================================
--- regrename.c (revision 3023)
+++ regrename.c (working copy)
@@ -1374,6 +1374,10 @@ maybe_mode_change (enum machine_mode ori
                   enum machine_mode new_mode, unsigned int regno,
                   unsigned int copy_regno ATTRIBUTE_UNUSED)
 {
+  if (GET_MODE_SIZE (copy_mode) == GET_MODE_SIZE (new_mode)
+      && hard_regno_nregs[copy_regno][copy_mode] ==
hard_regno_nregs[copy_regno][new_mode]
+      && hard_regno_nregs[regno][copy_mode] ==
hard_regno_nregs[copy_regno][new_mode])
+    return gen_rtx_raw_REG (new_mode, regno);
   if (orig_mode == new_mode)
     return gen_rtx_raw_REG (new_mode, regno);
   else if (mode_change_ok (orig_mode, new_mode, regno))
Index: config/rs6000/rs6000.md
===================================================================
--- config/rs6000/rs6000.md     (revision 3023)
+++ config/rs6000/rs6000.md     (working copy)
@@ -5247,10 +5247,17 @@ (define_insn_and_split "*extendsfdf2_fpr
    #
    fmr %0,%1
    lfs%U1%X1 %0,%1"
-  "&& reload_completed && REG_P (operands[1]) && REGNO (operands[0]) == REGNO
(operands[1])"
+  "&& reload_completed && REG_P (operands[1])"
   [(const_int 0)]
 {
-  emit_note (NOTE_INSN_DELETED);
+  if (REGNO (operands[0]) == REGNO (operands[1]))
+    emit_note (NOTE_INSN_DELETED);
+  else
+    {
+      rtx op0 = gen_rtx_REG (DFmode, REGNO (operands[0]));
+      rtx op1 = gen_rtx_REG (DFmode, REGNO (operands[1]));
+      emit_insn (gen_move_insn (op0, op1));
+    }
   DONE;
 }
   [(set_attr "type" "fp,fp,fpload")])


The rs6000 part is to tell the compiler what is really going on after register
allocator.  The regrename part allows to do a hard register copy propagation
after reload.
So we have:
(set (reg:SF 1) ... )
(set (reg:DF 2) (reg:DF 1))
(use (reg:DF 2))
After the rs6000.md patch.  Since the copy, is using the register in the larger
mode (DF), the last instruction should be just (use (reg:DF 1)).  This patch
allows for that.  


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17381