[Bug target/39942] Nonoptimal code - leaveq; xchg %ax,%ax; retq

["hjl dot tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #44 from hjl dot tools at gmail dot com  2009-05-15 23:05 -------
(In reply to comment #41)
> The 34 resp. 51 4 branches in 16 byte page with the 3 patches together made me
> look at one of the cases which was wrong and the problem is that cmp $0x1d, %al
> has too large get_attr_lenght (insn) returned, 3 instead of 2, because GCC
> thinks it has modrm byte when it has not.
> Testing:
> --- gcc/config/i386/i386.md.jj2009-05-13 08:42:51.000000000 +0200
> +++ gcc/config/i386/i386.md2009-05-15 18:06:40.000000000 +0200
> @@ -504,6 +504,9 @@
>   (and (eq_attr "type" "callv")
>        (match_operand 1 "constant_call_address_operand" ""))
>       (const_int 0)
> + (and (eq_attr "type" "alu,alu1,icmp,test")
> +      (match_operand 0 "ax_reg_operand" ""))
> +     (symbol_ref "(get_attr_length_immediate (insn) > (get_attr_mode (insn) !=
> MODE_QI))")
>   ]
>   (const_int 1)))
> 

"cmp imm,%al/%ax/%eax/%rax" doesn't have the modrm byte. I think
this patch works better:

--- i386.md.branch      2009-05-15 11:30:42.000000000 -0700
+++ i386.md     2009-05-15 14:44:11.000000000 -0700
@@ -504,6 +504,10 @@
         (and (eq_attr "type" "callv")
              (match_operand 1 "constant_call_address_operand" ""))
             (const_int 0)
+        (and (eq_attr "type" "alu,alu1,icmp,test")
+             (match_operand 0 "ax_reg_operand" "")
+             (match_operand 1 "immediate_operand" ""))
+            (const_int 0)
         ]
         (const_int 1)))



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39942