Hello!
According to [1], invalid canonization from ASHIFT to MULT was removed
a while ago. Some instruction patterns (like the one below) needs to
be updated from MULT to ASHIFT, and alpha was left behind.
(define_insn "*sadd<modesuffix>"
[(set (match_operand:I48MODE 0 "register_operand" "=r,r")
(plus:I48MODE
(mult:I48MODE (match_operand:I48MODE 1 "reg_not_elim_operand" "r,r")
(match_operand:I48MODE 2 "const48_operand" "I,I"))
(match_operand:I48MODE 3 "sext_add_operand" "rI,O")))]
The attached patch rewrites the affected patterns on alpha.
However, patch [1] introduced a combiner regression, where:
int s4l (int a, int b)
{
return a + b * 4;
}
doesn't get simplified to a single instruction anymore. The combiner tries with:
(set (reg:DI 76)
(sign_extend:DI (plus:SI (subreg:SI (ashift:DI (reg:DI 17 $17 [ b ])
(const_int 2 [0x2])) 0)
(reg:SI 16 $16 [ a ]))))
which doesn't match due to the SImode subreg of the inner RTX.
This can be solved by adding subreg to the insn pattern in alpha.md,
but it looks like a regression in the generic part of the compiler,
since gcc-5 was able to simplify this combination.
[1] https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01841.html
2018-01-04 Uros Bizjak <ubiz...@gmail.com>
PR target/83628
* config/alpha/alpha.md (*sadd<modesuffix>): Use ASHIFT
instead of MULT rtx. Update all corresponding splitters.
(*saddl_se): Ditto.
(*ssub<modesuffix>): Ditto.
(*ssubl_se): Ditto.
(*cmp_sadd_di): Update split patterns.
(*cmp_sadd_si): Ditto.
(*cmp_sadd_sidi): Ditto.
(*cmp_ssub_di): Ditto.
(*cmp_ssub_si): Ditto.
(*cmp_ssub_sidi): Ditto.
* config/alpha/predicates.md (const23_operand): New predicate.
* config/alpha/alpha.c (alpha_rtx_costs) [PLUS, MINUS]:
Look for ASHIFT, not MULT inner operand.
(alpha_split_conditional_move): Update for *sadd<modesuffix> change.
testsuite/ChangeLog:
2018-01-04 Uros Bizjak <ubiz...@gmail.com>
PR target/83628
* gcc.target/alpha/pr83628-1.c: New test.
* gcc.target/alpha/pr83628-2.c: Ditto.
Patch was bootstrapped and regression tested on alpha[,ev68]-linux-gnu.
Committed to mainline.
Uros.
