Hi!
This patch optimizes using peephole2 __sync_fetch_and_add (x, -N) == N
and __sync_add_and_fetch (x, N) == 0 by just doing lock {add,sub,inc,dec}
and testing flags, instead of lock xadd plus comparison.
The sync_old_add<mode> predicate change makes it possible to optimize
__sync_add_and_fetch with constant second argument to same
code as __sync_fetch_and_add. Doing it in peephole2 has a disadvantage
though, both that the 3 instructions need to be consecutive and
e.g. that xadd insn has to be supported by the CPU. Other alternative
would be to come up with a new bool builtin that would represent the
whole __sync_fetch_and_add (x, -N) == N operation (perhaps with dot or space
in its name to make it inaccessible), try to match it during some folding
and expand it using special optab.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
this way?
2011-05-16 Jakub Jelinek <ja...@redhat.com>
PR target/48986
* config/i386/sync.md (sync_old_add<mode>): Relax operand 2
predicate to allow CONST_INT.
(*sync_old_add_cmp<mode>): New insn and peephole2 for it.
--- gcc/config/i386/sync.md.jj 2010-05-21 11:46:29.000000000 +0200
+++ gcc/config/i386/sync.md 2011-05-16 14:42:08.000000000 +0200
@@ -170,11 +170,62 @@ (define_insn "sync_old_add<mode>"
[(match_operand:SWI 1 "memory_operand" "+m")] UNSPECV_XCHG))
(set (match_dup 1)
(plus:SWI (match_dup 1)
- (match_operand:SWI 2 "register_operand" "0")))
+ (match_operand:SWI 2 "nonmemory_operand" "0")))
(clobber (reg:CC FLAGS_REG))]
"TARGET_XADD"
"lock{%;} xadd{<imodesuffix>}\t{%0, %1|%1, %0}")
+(define_peephole2
+ [(set (match_operand:SWI 0 "register_operand" "")
+ (match_operand:SWI 2 "const_int_operand" ""))
+ (parallel [(set (match_dup 0)
+ (unspec_volatile:SWI
+ [(match_operand:SWI 1 "memory_operand" "")] UNSPECV_XCHG))
+ (set (match_dup 1)
+ (plus:SWI (match_dup 1)
+ (match_dup 0)))
+ (clobber (reg:CC FLAGS_REG))])
+ (set (reg:CCZ FLAGS_REG)
+ (compare:CCZ (match_dup 0)
+ (match_operand:SWI 3 "const_int_operand" "")))]
+ "peep2_reg_dead_p (3, operands[0])
+ && (unsigned HOST_WIDE_INT) INTVAL (operands[2])
+ == -(unsigned HOST_WIDE_INT) INTVAL (operands[3])
+ && !reg_overlap_mentioned_p (operands[0], operands[1])"
+ [(parallel [(set (reg:CCZ FLAGS_REG)
+ (compare:CCZ (unspec_volatile:SWI [(match_dup 1)]
+ UNSPECV_XCHG)
+ (match_dup 3)))
+ (set (match_dup 1)
+ (plus:SWI (match_dup 1)
+ (match_dup 2)))])])
+
+(define_insn "*sync_old_add_cmp<mode>"
+ [(set (reg:CCZ FLAGS_REG)
+ (compare:CCZ (unspec_volatile:SWI
+ [(match_operand:SWI 0 "memory_operand" "+m")]
+ UNSPECV_XCHG)
+ (match_operand:SWI 2 "const_int_operand" "i")))
+ (set (match_dup 0)
+ (plus:SWI (match_dup 0)
+ (match_operand:SWI 1 "const_int_operand" "i")))]
+ "(unsigned HOST_WIDE_INT) INTVAL (operands[1])
+ == -(unsigned HOST_WIDE_INT) INTVAL (operands[2])"
+{
+ if (TARGET_USE_INCDEC)
+ {
+ if (operands[1] == const1_rtx)
+ return "lock{%;} inc{<imodesuffix>}\t%0";
+ if (operands[1] == constm1_rtx)
+ return "lock{%;} dec{<imodesuffix>}\t%0";
+ }
+
+ if (x86_maybe_negate_const_int (&operands[1], <MODE>mode))
+ return "lock{%;} sub{<imodesuffix>}\t{%1, %0|%0, %1}";
+
+ return "lock{%;} add{<imodesuffix>}\t{%1, %0|%0, %1}";
+})
+
;; Recall that xchg implicitly sets LOCK#, so adding it again wastes space.
(define_insn "sync_lock_test_and_set<mode>"
[(set (match_operand:SWI 0 "register_operand" "=<r>")
Jakub
