[Bug target/77308] surprisingly large stack usage for sha512 on arm

[bernd.edlinger at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77308

--- Comment #5 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
Now I try to clear the out register when the shift < 32


Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c        (revision 239624)
+++ gcc/config/arm/arm.c        (working copy)
@@ -29159,6 +29159,7 @@ arm_emit_coreregs_64bit_shift (enum rtx_code code,
          /* Shifts by a constant less than 32.  */
          rtx reverse_amount = GEN_INT (32 - INTVAL (amount));

+         emit_insn (SET (out, const0_rtx));
          emit_insn (SET (out_down, LSHIFT (code, in_down, amount)));
          emit_insn (SET (out_down,
                          ORR (REV_LSHIFT (code, in_up, reverse_amount),
@@ -29170,12 +29171,11 @@ arm_emit_coreregs_64bit_shift (enum rtx_code code,
          /* Shifts by a constant greater than 31.  */
          rtx adj_amount = GEN_INT (INTVAL (amount) - 32);

+         emit_insn (SET (out, const0_rtx));
          emit_insn (SET (out_down, SHIFT (code, in_up, adj_amount)));
          if (code == ASHIFTRT)
            emit_insn (gen_ashrsi3 (out_up, in_up,
                                    GEN_INT (31)));
-         else
-           emit_insn (SET (out_up, const0_rtx));
        }
     }
   else


result: the stack use goes down from 2960 to 2320
note: this SET is simply redundant, but it makes the out
well-defined from the beginning.