Re: [PATCH, Atom] Improve AGU stalls avoidance optimization

[Uros Bizjak <ubizjak at gmail dot com>]

... Sent again, with correct Cc and subject line ...

Hello!

> Here is a patch which adds few more splits for AGU stalls avoidance on
> Atom. It also fixes cost model and detects AGU stalls more
> efficiently.
>
> Bootstrapped and checked on x86_64-linux.
>
> 2011-09-02 ?Enkovich Ilya ?<ilya.enkovich@intel.com>
>
> ? ? ? * config/i386/i386-protos.h (ix86_lea_outperforms): New.
> ? ? ? (ix86_avoid_lea_for_add): Likewise.
> ? ? ? (ix86_avoid_lea_for_addr): Likewise.
> ? ? ? (ix86_split_lea_for_addr): Likewise.
>
> ? ? ? * config/i386/i386.c (LEA_MAX_STALL): New.
> ? ? ? (increase_distance): Likewise.
> ? ? ? (insn_defines_reg): Likewise.
> ? ? ? (insn_uses_reg_mem): Likewise.
> ? ? ? (distance_non_agu_define_in_bb): Likewise.
> ? ? ? (distance_agu_use_in_bb): Likewise.
> ? ? ? (ix86_lea_outperforms): Likewise.
> ? ? ? (ix86_ok_to_clobber_flags): Likewise.
> ? ? ? (ix86_avoid_lea_for_add): Likewise.
> ? ? ? (ix86_avoid_lea_for_addr): Likewise.
> ? ? ? (ix86_split_lea_for_addr): Likewise.
> ? ? ? (distance_non_agu_define): Search in pred BBs added.
> ? ? ? (distance_agu_use): Search in succ BBs added.
> ? ? ? (IX86_LEA_PRIORITY): Value changed from 2 to 0.
> ? ? ? (LEA_SEARCH_THRESHOLD): Now depends on LEA_MAX_STALL.
> ? ? ? (ix86_lea_for_add_ok): Use ix86_lea_outperforms to make decision.
>
> ? ? ? * config/i386/i386.md: Splits added to transform lea into a
> ? ? ? sequence of instructions.

Did you also test on x32 ? H.J.'s x32 page [1] currently says that
Atom LEA optimization is disabled on x32 for some reason.

The patch looks OK to me, with a few nits below.

[1] https://sites.google.com/site/x32abi/

--- a/gcc/config/i386/i386-protos.h
+++ b/gcc/config/i386/i386-protos.h

+bool
+ix86_avoid_lea_for_addr (rtx insn, rtx operands[])
+{
+ ?unsigned int regno0 = true_regnum (operands[0]) ;
+ ?unsigned int regno1 = -1;
+ ?unsigned int regno2 = -1;

Use INVALID_REGNUM here.

+extern void
+ix86_split_lea_for_addr (rtx operands[], enum machine_mode mode)
+{

Missing comment.

--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -5777,6 +5777,41 @@
? ? ? ? (const_string "none")))
? ?(set_attr "mode" "QI")])

+;; Split non destructive adds if we cannot use lea.
+(define_split
+ ?[(set (match_operand:SWI48 0 "register_operand" "")
+ ? ? ? (plus:SWI48 (match_operand:SWI48 1 "register_operand" "")
+ ? ? ? ? ? ? ?(match_operand:SWI48 2 "nonmemory_operand" "")))
+ ? (clobber (reg:CC FLAGS_REG))]
+ ?"reload_completed && ix86_avoid_lea_for_add (insn, operands)"
+ ?[(set (match_dup 0) (match_dup 1))
+ ? (parallel [(set (match_dup 0) (plus:<MODE> (match_dup 0) (match_dup 2)))
+ ? ? ? ? ? ? (clobber (reg:CC FLAGS_REG))])
+ ?]
+)

Put all closing braces on one line:

? ? ? ? ? ? ?(clobber (reg:CC FLAGS_REG))])])

+;; Split lea into one or more ALU instructions if profitable.
+(define_split
+ ?[(set (match_operand:SI 0 "register_operand" "")
+ ? ? ? (subreg:SI (match_operand:DI 1 "lea_address_operand" "") 0))]
+ ?"reload_completed && ix86_avoid_lea_for_addr (insn, operands)"
+ ?[(const_int 0)]
+{
+ ?ix86_split_lea_for_addr (operands, SImode);
+ ?DONE;
+})

This is valid only for TARGET_64BIT.

Please note that x32 adds quite some different LEA patterns (see
i386.md, line 5466+). I suggest you merge your splitters with these
define_insn patterns into define_insn_and_split, adding "&&
reload_completed && ix86_avoid_lea_for_addr (insn, operands)" as a
split condition.

Uros.