https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127452
Hongtao Liu <liuhongt at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |liuhongt at gcc dot gnu.org
--- Comment #13 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
For the scalar part
typedef unsigned long long u64;
u64
mulh (u64 a, u64 b)
{
return ((unsigned __int128) a * b) >> 64;
}
gcc -O2 -march=x86-64-v2 -mbmi2
"mulh":
mov rax, rdi
mul rsi
mov rax, rdx
ret
dump of reload:
(insn 8 21 15 2 (parallel [
(set (reg:DI 1 dx [orig:106 highparttmp_9 ] [106])
(umul_highpart:DI (reg:DI 0 ax [orig:108 a ] [108])
(reg:DI 4 si [orig:109 b ] [109])))
(clobber (reg:DI 0 ax [orig:108 a ] [108]))
(clobber (reg:CC 17 flags))
]) "/app/example.c":6:38 660 {umuldi3_highpart}
(nil))
1937;; BMI2 MULX highpart-only pattern. Uses MULX to get only the high part.
11938;; When both output operands are identical, MULX writes the high half to
that
11939;; register, so no scratch register is needed. This avoids the mov from
rdx
11940;; after mulq when only the high part is needed.
11941(define_insn "*bmi2_umul<mode>3_highpart"
11942 [(set (match_operand:DWIH 0 "register_operand" "=r")
11943 (umul_highpart:DWIH
11944 (match_operand:DWIH 1 "register_operand" "d")
11945 (match_operand:DWIH 2 "nonimmediate_operand" "rm")))]
11946 "TARGET_BMI2"
11947 "mulx\t{%2, %0, %0|%0, %0, %2}"
Why this is not matched.
