This patch adds a straight forward combine pattern and split for int + 2*byte
as frequently seen with accesses to int-arrays with byte offset.
Ok for trunk?
Johann
* config/avr/avr.md (*umaddqihi4.2): New insn-and-split.
Index: config/avr/avr.md
===================================================================
--- config/avr/avr.md (revision 184887)
+++ config/avr/avr.md (working copy)
@@ -1692,6 +1692,30 @@ (define_insn "*<any_extend:extend_su><an
;; Handle small constants
+;; Special case of a += 2*b as frequently seen with accesses to int arrays.
+;; This is shorter, faster than MUL and has lower register pressure.
+
+(define_insn_and_split "*umaddqihi4.2"
+ [(set (match_operand:HI 0 "register_operand" "=r")
+ (plus:HI (mult:HI (zero_extend:HI (match_operand:QI 1 "register_operand" "r"))
+ (const_int 2))
+ (match_operand:HI 2 "register_operand" "r")))]
+ "AVR_HAVE_MUL
+ && !reload_completed
+ && !reg_overlap_mentioned_p (operands[0], operands[1])"
+ { gcc_unreachable(); }
+ "&& 1"
+ [(set (match_dup 0)
+ (match_dup 2))
+ ; *addhi3_zero_extend
+ (set (match_dup 0)
+ (plus:HI (zero_extend:HI (match_dup 1))
+ (match_dup 0)))
+ ; *addhi3_zero_extend
+ (set (match_dup 0)
+ (plus:HI (zero_extend:HI (match_dup 1))
+ (match_dup 0)))])
+
;; "umaddqihi4.uconst"
;; "maddqihi4.sconst"
(define_insn_and_split "*<extend_u>maddqihi4.<extend_su>const"
